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  25 <div class="section">
  26 <div class="titlepage"><div><div><h2 class="title" style="clear: both">
  27 <a name="interprocess.allocators_containers"></a><a class="link" href="allocators_containers.html" title="Allocators, containers and memory allocation algorithms">Allocators, containers
  28     and memory allocation algorithms</a>
  29 </h2></div></div></div>
  30 <div class="toc"><dl class="toc">
  31 <dt><span class="section"><a href="allocators_containers.html#interprocess.allocators_containers.allocator_introduction">Introduction
  32       to Interprocess allocators</a></span></dt>
  33 <dt><span class="section"><a href="allocators_containers.html#interprocess.allocators_containers.stl_allocators_segregated_storage">Segregated
  34       storage node allocators</a></span></dt>
  35 <dt><span class="section"><a href="allocators_containers.html#interprocess.allocators_containers.stl_allocators_adaptive">Adaptive
  36       pool node allocators</a></span></dt>
  37 <dt><span class="section"><a href="allocators_containers.html#interprocess.allocators_containers.containers_explained">Interprocess
  38       and containers in managed memory segments</a></span></dt>
  39 <dt><span class="section"><a href="allocators_containers.html#interprocess.allocators_containers.additional_containers">Boost
  40       containers compatible with Boost.Interprocess</a></span></dt>
  41 </dl></div>
  42 <div class="section">
  43 <div class="titlepage"><div><div><h3 class="title">
  44 <a name="interprocess.allocators_containers.allocator_introduction"></a><a class="link" href="allocators_containers.html#interprocess.allocators_containers.allocator_introduction" title="Introduction to Interprocess allocators">Introduction
  45       to Interprocess allocators</a>
  46 </h3></div></div></div>
  47 <div class="toc"><dl class="toc">
  48 <dt><span class="section"><a href="allocators_containers.html#interprocess.allocators_containers.allocator_introduction.allocator_properties">Properties
  49         of <span class="bold"><strong>Boost.Interprocess</strong></span> allocators</a></span></dt>
  50 <dt><span class="section"><a href="allocators_containers.html#interprocess.allocators_containers.allocator_introduction.allocator_swapping">Swapping
  51         Boost.Interprocess allocators</a></span></dt>
  52 <dt><span class="section"><a href="allocators_containers.html#interprocess.allocators_containers.allocator_introduction.allocator">allocator:
  53         A general purpose allocator for managed memory segments</a></span></dt>
  54 </dl></div>
  55 <p>
  56         As seen, <span class="bold"><strong>Boost.Interprocess</strong></span> offers raw memory
  57         allocation and object construction using managed memory segments (managed
  58         shared memory, managed mapped files...) and one of the first user requests
  59         is the use of containers in managed shared memories. To achieve this, <span class="bold"><strong>Boost.Interprocess</strong></span> makes use of managed memory segment's
  60         memory allocation algorithms to build several memory allocation schemes,
  61         including general purpose and node allocators.
  62       </p>
  63 <p>
  64         <span class="bold"><strong>Boost.Interprocess</strong></span> STL compatible allocators
  65         are configurable via template parameters. Allocators define their <code class="computeroutput"><span class="identifier">pointer</span></code> typedef based on the <code class="computeroutput"><span class="identifier">void_pointer</span></code> typedef of the segment manager
  66         passed as template argument. When this <code class="computeroutput"><span class="identifier">segment_manager</span><span class="special">::</span><span class="identifier">void_pointer</span></code>
  67         is a relative pointer, (for example, <code class="computeroutput"><span class="identifier">offset_ptr</span><span class="special">&lt;</span><span class="keyword">void</span><span class="special">&gt;</span></code>)
  68         the user can place these allocators in memory mapped in different base addresses
  69         in several processes.
  70       </p>
  71 <div class="section">
  72 <div class="titlepage"><div><div><h4 class="title">
  73 <a name="interprocess.allocators_containers.allocator_introduction.allocator_properties"></a><a class="link" href="allocators_containers.html#interprocess.allocators_containers.allocator_introduction.allocator_properties" title="Properties of Boost.Interprocess allocators">Properties
  74         of <span class="bold"><strong>Boost.Interprocess</strong></span> allocators</a>
  75 </h4></div></div></div>
  76 <p>
  77           Container allocators are normally default-constructible because the are
  78           stateless. <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">allocator</span></code> and <span class="bold"><strong>Boost.Pool's</strong></span>
  79           <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">pool_allocator</span></code>/<code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">fast_pool_allocator</span></code>
  80           are examples of default-constructible allocators.
  81         </p>
  82 <p>
  83           On the other hand, <span class="bold"><strong>Boost.Interprocess</strong></span>
  84           allocators need to allocate memory from a concrete memory segment and not
  85           from a system-wide memory source (like the heap). <span class="bold"><strong>Boost.Interprocess</strong></span>
  86           allocators are <span class="bold"><strong>stateful</strong></span>, which means that
  87           they must be configured to tell them where the shared memory or the memory
  88           mapped file is.
  89         </p>
  90 <p>
  91           This information is transmitted at compile-time and run-time: The allocators
  92           receive a template parameter defining the type of the segment manager and
  93           their constructor receive a pointer to the segment manager of the managed
  94           memory segment where the user wants to allocate the values.
  95         </p>
  96 <p>
  97           <span class="bold"><strong>Boost.Interprocess</strong></span> allocators have <span class="bold"><strong>no default-constructors</strong></span> and containers must be explicitly
  98           initialized with a configured allocator:
  99         </p>
 100 <pre class="programlisting"><span class="comment">//The allocators must be templatized with the segment manager type</span>
 101 <span class="keyword">typedef</span> <span class="identifier">any_interprocess_allocator</span>
 102    <span class="special">&lt;</span><span class="keyword">int</span><span class="special">,</span> <span class="identifier">managed_shared_memory</span><span class="special">::</span><span class="identifier">segment_manager</span><span class="special">,</span> <span class="special">...&gt;</span> <span class="identifier">Allocator</span><span class="special">;</span>
 103
 104 <span class="comment">//The allocator must be constructed with a pointer to the segment manager</span>
 105 <span class="identifier">Allocator</span> <span class="identifier">alloc_instance</span> <span class="special">(</span><span class="identifier">segment</span><span class="special">.</span><span class="identifier">get_segment_manager</span><span class="special">(),</span> <span class="special">...);</span>
 106
 107 <span class="comment">//Containers must be initialized with a configured allocator</span>
 108 <span class="keyword">typedef</span> <span class="identifier">my_list</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">,</span> <span class="identifier">Allocator</span><span class="special">&gt;</span> <span class="identifier">MyIntList</span><span class="special">;</span>
 109 <span class="identifier">MyIntList</span> <span class="identifier">mylist</span><span class="special">(</span><span class="identifier">alloc_inst</span><span class="special">);</span>
 110
 111 <span class="comment">//This would lead to a compilation error, because</span>
 112 <span class="comment">//the allocator has no default constructor</span>
 113 <span class="comment">//MyIntList mylist;</span>
 114 </pre>
 115 <p>
 116           <span class="bold"><strong>Boost.Interprocess</strong></span> allocators also have
 117           a <code class="computeroutput"><span class="identifier">get_segment_manager</span><span class="special">()</span></code>
 118           function that returns the underlying segment manager that they have received
 119           in the constructor:
 120         </p>
 121 <pre class="programlisting"><span class="identifier">Allocator</span><span class="special">::</span><span class="identifier">segment_manager</span> <span class="identifier">s</span> <span class="special">=</span> <span class="identifier">alloc_instance</span><span class="special">.</span><span class="identifier">get_segment_manager</span><span class="special">();</span>
 122 <span class="identifier">AnotherType</span> <span class="special">*</span><span class="identifier">a</span> <span class="special">=</span> <span class="identifier">s</span><span class="special">-&gt;</span><span class="identifier">construct</span><span class="special">&lt;</span><span class="identifier">AnotherType</span><span class="special">&gt;(</span><span class="identifier">anonymous_instance</span><span class="special">)(/*</span><span class="identifier">Parameters</span><span class="special">*/);</span>
 123 </pre>
 124 </div>
 125 <div class="section">
 126 <div class="titlepage"><div><div><h4 class="title">
 127 <a name="interprocess.allocators_containers.allocator_introduction.allocator_swapping"></a><a class="link" href="allocators_containers.html#interprocess.allocators_containers.allocator_introduction.allocator_swapping" title="Swapping Boost.Interprocess allocators">Swapping
 128         Boost.Interprocess allocators</a>
 129 </h4></div></div></div>
 130 <p>
 131           When swapping STL containers, there is an active discussion on what to
 132           do with the allocators. Some STL implementations, for example Dinkumware
 133           from Visual .NET 2003, perform a deep swap of the whole container through
 134           a temporary when allocators are not equal. The <a href="http://www.open-std.org/JTC1/SC22/WG21/docs/papers/2004/n1599.html" target="_top">proposed
 135           resolution</a> to container swapping is that allocators should be swapped
 136           in a non-throwing way.
 137         </p>
 138 <p>
 139           Unfortunately, this approach is not valid with shared memory. Using heap
 140           allocators, if Group1 of node allocators share a common segregated storage,
 141           and Group2 share another common segregated storage, a simple pointer swapping
 142           is needed to swap an allocator of Group1 and another allocator of Group2.
 143           But when the user wants to swap two shared memory allocators, each one
 144           placed in a different shared memory segment, this is not possible. As generally
 145           shared memory is mapped in different addresses in each process, a pointer
 146           placed in one segment can't point to any object placed in other shared
 147           memory segment, since in each process, the distance between the segments
 148           is different. However, if both shared memory allocators are in the same
 149           segment, a non-throwing swap is possible, just like heap allocators.
 150         </p>
 151 <p>
 152           Until a final resolution is achieved. <span class="bold"><strong>Boost.Interprocess</strong></span>
 153           allocators implement a non-throwing swap function that swaps internal pointers.
 154           If an allocator placed in a shared memory segment is swapped with other
 155           placed in a different shared memory segment, the result is undefined. But
 156           a crash is quite sure.
 157         </p>
 158 </div>
 159 <div class="section">
 160 <div class="titlepage"><div><div><h4 class="title">
 161 <a name="interprocess.allocators_containers.allocator_introduction.allocator"></a><a class="link" href="allocators_containers.html#interprocess.allocators_containers.allocator_introduction.allocator" title="allocator: A general purpose allocator for managed memory segments">allocator:
 162         A general purpose allocator for managed memory segments</a>
 163 </h4></div></div></div>
 164 <p>
 165           The <code class="computeroutput"><a class="link" href="../boost/interprocess/allocator.html" title="Class template allocator">allocator</a></code>
 166           class defines an allocator class that uses the managed memory segment's
 167           algorithm to allocate and deallocate memory. This is achieved through the
 168           <span class="bold"><strong>segment manager</strong></span> of the managed memory
 169           segment. This allocator is the equivalent for managed memory segments of
 170           the standard <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">allocator</span></code>. <code class="computeroutput"><a class="link" href="../boost/interprocess/allocator.html" title="Class template allocator">allocator</a></code>
 171           is templatized with the allocated type, and the segment manager.
 172         </p>
 173 <p>
 174           <span class="bold"><strong>Equality:</strong></span> Two <code class="computeroutput"><a class="link" href="../boost/interprocess/allocator.html" title="Class template allocator">allocator</a></code>
 175           instances constructed with the same segment manager compare equal. If an
 176           instance is created using copy constructor, that instance compares equal
 177           with the original one.
 178         </p>
 179 <p>
 180           <span class="bold"><strong>Allocation thread-safety:</strong></span> Allocation and
 181           deallocation are implemented as calls to the segment manager's allocation
 182           function so the allocator offers the same thread-safety as the segment
 183           manager.
 184         </p>
 185 <p>
 186           To use <code class="computeroutput"><a class="link" href="../boost/interprocess/allocator.html" title="Class template allocator">allocator</a></code>
 187           you must include the following header:
 188         </p>
 189 <pre class="programlisting"><span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">interprocess</span><span class="special">/</span><span class="identifier">allocators</span><span class="special">/</span><span class="identifier">allocator</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
 190 </pre>
 191 <p>
 192           <code class="computeroutput"><a class="link" href="../boost/interprocess/allocator.html" title="Class template allocator">allocator</a></code> has
 193           the following declaration:
 194         </p>
 195 <pre class="programlisting"><span class="keyword">namespace</span> <span class="identifier">boost</span> <span class="special">{</span>
 196 <span class="keyword">namespace</span> <span class="identifier">interprocess</span> <span class="special">{</span>
 197
 198 <span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">,</span> <span class="keyword">class</span> <span class="identifier">SegmentManager</span><span class="special">&gt;</span>
 199 <span class="keyword">class</span> <span class="identifier">allocator</span><span class="special">;</span>
 200
 201 <span class="special">}</span>  <span class="comment">//namespace interprocess {</span>
 202 <span class="special">}</span>  <span class="comment">//namespace boost {</span>
 203 </pre>
 204 <p>
 205           The allocator just provides the needed typedefs and forwards all allocation
 206           and deallocation requests to the segment manager passed in the constructor,
 207           just like <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">allocator</span></code> forwards the requests to <code class="computeroutput"><span class="keyword">operator</span> <span class="keyword">new</span><span class="special">[]</span></code>.
 208         </p>
 209 <p>
 210           Using <code class="computeroutput"><a class="link" href="../boost/interprocess/allocator.html" title="Class template allocator">allocator</a></code>
 211           is straightforward:
 212         </p>
 213 <p>
 214 </p>
 215 <pre class="programlisting"><span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">interprocess</span><span class="special">/</span><span class="identifier">managed_shared_memory</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
 216 <span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">interprocess</span><span class="special">/</span><span class="identifier">allocators</span><span class="special">/</span><span class="identifier">allocator</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
 217 <span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">cassert</span><span class="special">&gt;</span>
 218
 219 <span class="keyword">using</span> <span class="keyword">namespace</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">;</span>
 220
 221 <span class="keyword">int</span> <span class="identifier">main</span> <span class="special">()</span>
 222 <span class="special">{</span>
 223    <span class="comment">//Remove shared memory on construction and destruction</span>
 224    <span class="keyword">struct</span> <span class="identifier">shm_remove</span>
 225    <span class="special">{</span>
 226       <span class="identifier">shm_remove</span><span class="special">()</span> <span class="special">{</span> <span class="identifier">shared_memory_object</span><span class="special">::</span><span class="identifier">remove</span><span class="special">(</span><span class="string">"MySharedMemory"</span><span class="special">);</span> <span class="special">}</span>
 227       <span class="special">~</span><span class="identifier">shm_remove</span><span class="special">(){</span> <span class="identifier">shared_memory_object</span><span class="special">::</span><span class="identifier">remove</span><span class="special">(</span><span class="string">"MySharedMemory"</span><span class="special">);</span> <span class="special">}</span>
 228    <span class="special">}</span> <span class="identifier">remover</span><span class="special">;</span>
 229
 230    <span class="comment">//Create shared memory</span>
 231    <span class="identifier">managed_shared_memory</span> <span class="identifier">segment</span><span class="special">(</span><span class="identifier">create_only</span><span class="special">,</span>
 232                                  <span class="string">"MySharedMemory"</span><span class="special">,</span>  <span class="comment">//segment name</span>
 233                                  <span class="number">65536</span><span class="special">);</span>
 234
 235    <span class="comment">//Create an allocator that allocates ints from the managed segment</span>
 236    <span class="identifier">allocator</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">,</span> <span class="identifier">managed_shared_memory</span><span class="special">::</span><span class="identifier">segment_manager</span><span class="special">&gt;</span>
 237       <span class="identifier">allocator_instance</span><span class="special">(</span><span class="identifier">segment</span><span class="special">.</span><span class="identifier">get_segment_manager</span><span class="special">());</span>
 238
 239    <span class="comment">//Copy constructed allocator is equal</span>
 240    <span class="identifier">allocator</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">,</span> <span class="identifier">managed_shared_memory</span><span class="special">::</span><span class="identifier">segment_manager</span><span class="special">&gt;</span>
 241       <span class="identifier">allocator_instance2</span><span class="special">(</span><span class="identifier">allocator_instance</span><span class="special">);</span>
 242    <span class="identifier">assert</span><span class="special">(</span><span class="identifier">allocator_instance2</span> <span class="special">==</span> <span class="identifier">allocator_instance</span><span class="special">);</span>
 243
 244    <span class="comment">//Allocate and deallocate memory for 100 ints</span>
 245    <span class="identifier">allocator_instance2</span><span class="special">.</span><span class="identifier">deallocate</span><span class="special">(</span><span class="identifier">allocator_instance</span><span class="special">.</span><span class="identifier">allocate</span><span class="special">(</span><span class="number">100</span><span class="special">),</span> <span class="number">100</span><span class="special">);</span>
 246
 247    <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span>
 248 <span class="special">}</span>
 249 </pre>
 250 <p>
 251         </p>
 252 </div>
 253 </div>
 254 <div class="section">
 255 <div class="titlepage"><div><div><h3 class="title">
 256 <a name="interprocess.allocators_containers.stl_allocators_segregated_storage"></a><a class="link" href="allocators_containers.html#interprocess.allocators_containers.stl_allocators_segregated_storage" title="Segregated storage node allocators">Segregated
 257       storage node allocators</a>
 258 </h3></div></div></div>
 259 <div class="toc"><dl class="toc">
 260 <dt><span class="section"><a href="allocators_containers.html#interprocess.allocators_containers.stl_allocators_segregated_storage.segregated_allocators_common">Additional
 261         parameters and functions of segregated storage node allocators</a></span></dt>
 262 <dt><span class="section"><a href="allocators_containers.html#interprocess.allocators_containers.stl_allocators_segregated_storage.node_allocator">node_allocator:
 263         A process-shared segregated storage</a></span></dt>
 264 <dt><span class="section"><a href="allocators_containers.html#interprocess.allocators_containers.stl_allocators_segregated_storage.private_node_allocator">private_node_allocator:
 265         a private segregated storage</a></span></dt>
 266 <dt><span class="section"><a href="allocators_containers.html#interprocess.allocators_containers.stl_allocators_segregated_storage.cached_node_allocator">cached_node_allocator:
 267         caching nodes to avoid overhead</a></span></dt>
 268 </dl></div>
 269 <p>
 270         Variable size memory algorithms waste some space in management information
 271         for each allocation. Sometimes, usually for small objects, this is not acceptable.
 272         Memory algorithms can also fragment the managed memory segment under some
 273         allocation and deallocation schemes, reducing their performance. When allocating
 274         many objects of the same type, a simple segregated storage becomes a fast
 275         and space-friendly allocator, as explained in the <a href="http://www.boost.org/libs/pool/" target="_top"><span class="bold"><strong>Boost.Pool</strong></span></a> library.
 276       </p>
 277 <p>
 278         Segregate storage node allocators allocate large memory chunks from a general
 279         purpose memory allocator and divide that chunk into several nodes. No bookkeeping
 280         information is stored in the nodes to achieve minimal memory waste: free
 281         nodes are linked using a pointer constructed in the memory of the node.
 282       </p>
 283 <p>
 284         <span class="bold"><strong>Boost.Interprocess</strong></span> offers 3 allocators based
 285         on this segregated storage algorithm: <code class="computeroutput"><a class="link" href="../boost/interprocess/node_allocator.html" title="Class template node_allocator">node_allocator</a></code>,
 286         <code class="computeroutput"><a class="link" href="../boost/interprocess/private_node_allocator.html" title="Class template private_node_allocator">private_node_allocator</a></code>
 287         and <code class="computeroutput"><a class="link" href="../boost/interprocess/cached_node_allocator.html" title="Class template cached_node_allocator">cached_node_allocator</a></code>.
 288       </p>
 289 <p>
 290         To know the details of the implementation of of the segregated storage pools
 291         see the <a class="link" href="architecture.html#interprocess.architecture.allocators_containers.implementation_segregated_storage_pools" title="Implementation of Boost.Interprocess segregated storage pools">Implementation
 292         of <span class="bold"><strong>Boost.Interprocess</strong></span> segregated storage
 293         pools</a> section.
 294       </p>
 295 <div class="section">
 296 <div class="titlepage"><div><div><h4 class="title">
 297 <a name="interprocess.allocators_containers.stl_allocators_segregated_storage.segregated_allocators_common"></a><a class="link" href="allocators_containers.html#interprocess.allocators_containers.stl_allocators_segregated_storage.segregated_allocators_common" title="Additional parameters and functions of segregated storage node allocators">Additional
 298         parameters and functions of segregated storage node allocators</a>
 299 </h4></div></div></div>
 300 <p>
 301           <code class="computeroutput"><a class="link" href="../boost/interprocess/node_allocator.html" title="Class template node_allocator">node_allocator</a></code>,
 302           <code class="computeroutput"><a class="link" href="../boost/interprocess/private_node_allocator.html" title="Class template private_node_allocator">private_node_allocator</a></code>
 303           and <code class="computeroutput"><a class="link" href="../boost/interprocess/cached_node_allocator.html" title="Class template cached_node_allocator">cached_node_allocator</a></code>
 304           implement the standard allocator interface and the functions explained
 305           in the <a class="link" href="allocators_containers.html#interprocess.allocators_containers.allocator_introduction.allocator_properties" title="Properties of Boost.Interprocess allocators">Properties
 306           of Boost.Interprocess allocators</a>.
 307         </p>
 308 <p>
 309           All these allocators are templatized by 3 parameters:
 310         </p>
 311 <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
 312 <li class="listitem">
 313               <code class="computeroutput"><span class="keyword">class</span> <span class="identifier">T</span></code>:
 314               The type to be allocated.
 315             </li>
 316 <li class="listitem">
 317               <code class="computeroutput"><span class="keyword">class</span> <span class="identifier">SegmentManager</span></code>:
 318               The type of the segment manager that will be passed in the constructor.
 319             </li>
 320 <li class="listitem">
 321               <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">NodesPerChunk</span></code>:
 322               The number of nodes that a memory chunk will contain. This value will
 323               define the size of the memory the pool will request to the segment
 324               manager when the pool runs out of nodes. This parameter has a default
 325               value.
 326             </li>
 327 </ul></div>
 328 <p>
 329           These allocators also offer the <code class="computeroutput"><span class="identifier">deallocate_free_chunks</span><span class="special">()</span></code> function. This function will traverse
 330           all the memory chunks of the pool and will return to the managed memory
 331           segment the free chunks of memory. If this function is not used, deallocating
 332           the free chunks does not happen until the pool is destroyed so the only
 333           way to return memory allocated by the pool to the segment before destructing
 334           the pool is calling manually this function. This function is quite time-consuming
 335           because it has quadratic complexity (O(N^2)).
 336         </p>
 337 </div>
 338 <div class="section">
 339 <div class="titlepage"><div><div><h4 class="title">
 340 <a name="interprocess.allocators_containers.stl_allocators_segregated_storage.node_allocator"></a><a class="link" href="allocators_containers.html#interprocess.allocators_containers.stl_allocators_segregated_storage.node_allocator" title="node_allocator: A process-shared segregated storage">node_allocator:
 341         A process-shared segregated storage</a>
 342 </h4></div></div></div>
 343 <p>
 344           For heap-memory node allocators (like <span class="bold"><strong>Boost.Pool's</strong></span>
 345           <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">fast_pool_allocator</span></code> usually a global,
 346           thread-shared singleton pool is used for each node size. This is not possible
 347           if you try to share a node allocator between processes. To achieve this
 348           sharing <code class="computeroutput"><a class="link" href="../boost/interprocess/node_allocator.html" title="Class template node_allocator">node_allocator</a></code>
 349           uses the segment manager's unique type allocation service (see <a class="link" href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_memory_segment_features.unique" title="Unique instance construction">Unique
 350           instance construction</a> section).
 351         </p>
 352 <p>
 353           In the initialization, a <code class="computeroutput"><a class="link" href="../boost/interprocess/node_allocator.html" title="Class template node_allocator">node_allocator</a></code>
 354           object searches this unique object in the segment. If it is not preset,
 355           it builds one. This way, all <code class="computeroutput"><a class="link" href="../boost/interprocess/node_allocator.html" title="Class template node_allocator">node_allocator</a></code>
 356           objects built inside a memory segment share a unique memory pool.
 357         </p>
 358 <p>
 359           The common segregated storage is not only shared between node_allocators
 360           of the same type, but it is also shared between all node allocators that
 361           allocate objects of the same size, for example, <span class="bold"><strong>node_allocator&lt;uint32&gt;</strong></span>
 362           and <span class="bold"><strong>node_allocator&lt;float32&gt;</strong></span>. This
 363           saves a lot of memory but also imposes an synchronization overhead for
 364           each node allocation.
 365         </p>
 366 <p>
 367           The dynamically created common segregated storage integrates a reference
 368           count so that a <code class="computeroutput"><a class="link" href="../boost/interprocess/node_allocator.html" title="Class template node_allocator">node_allocator</a></code>
 369           can know if any other <code class="computeroutput"><a class="link" href="../boost/interprocess/node_allocator.html" title="Class template node_allocator">node_allocator</a></code>
 370           is attached to the same common segregated storage. When the last allocator
 371           attached to the pool is destroyed, the pool is destroyed.
 372         </p>
 373 <p>
 374           <span class="bold"><strong>Equality:</strong></span> Two <code class="computeroutput"><a class="link" href="../boost/interprocess/node_allocator.html" title="Class template node_allocator">node_allocator</a></code>
 375           instances constructed with the same segment manager compare equal. If an
 376           instance is created using copy constructor, that instance compares equal
 377           with the original one.
 378         </p>
 379 <p>
 380           <span class="bold"><strong>Allocation thread-safety:</strong></span> Allocation and
 381           deallocation are implemented as calls to the shared pool. The shared pool
 382           offers the same synchronization guarantees as the segment manager.
 383         </p>
 384 <p>
 385           To use <code class="computeroutput"><a class="link" href="../boost/interprocess/node_allocator.html" title="Class template node_allocator">node_allocator</a></code>,
 386           you must include the following header:
 387         </p>
 388 <pre class="programlisting"><span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">interprocess</span><span class="special">/</span><span class="identifier">allocators</span><span class="special">/</span><span class="identifier">node_allocator</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
 389 </pre>
 390 <p>
 391           <code class="computeroutput"><a class="link" href="../boost/interprocess/node_allocator.html" title="Class template node_allocator">node_allocator</a></code>
 392           has the following declaration:
 393         </p>
 394 <pre class="programlisting"><span class="keyword">namespace</span> <span class="identifier">boost</span> <span class="special">{</span>
 395 <span class="keyword">namespace</span> <span class="identifier">interprocess</span> <span class="special">{</span>
 396
 397 <span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">,</span> <span class="keyword">class</span> <span class="identifier">SegmentManager</span><span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">NodesPerChunk</span> <span class="special">=</span> <span class="special">...&gt;</span>
 398 <span class="keyword">class</span> <span class="identifier">node_allocator</span><span class="special">;</span>
 399
 400 <span class="special">}</span>  <span class="comment">//namespace interprocess {</span>
 401 <span class="special">}</span>  <span class="comment">//namespace boost {</span>
 402 </pre>
 403 <p>
 404           An example using <code class="computeroutput"><a class="link" href="../boost/interprocess/node_allocator.html" title="Class template node_allocator">node_allocator</a></code>:
 405         </p>
 406 <p>
 407 </p>
 408 <pre class="programlisting"><span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">interprocess</span><span class="special">/</span><span class="identifier">managed_shared_memory</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
 409 <span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">interprocess</span><span class="special">/</span><span class="identifier">allocators</span><span class="special">/</span><span class="identifier">node_allocator</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
 410 <span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">cassert</span><span class="special">&gt;</span>
 411
 412 <span class="keyword">using</span> <span class="keyword">namespace</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">;</span>
 413
 414 <span class="keyword">int</span> <span class="identifier">main</span> <span class="special">()</span>
 415 <span class="special">{</span>
 416    <span class="comment">//Remove shared memory on construction and destruction</span>
 417    <span class="keyword">struct</span> <span class="identifier">shm_remove</span>
 418    <span class="special">{</span>
 419       <span class="identifier">shm_remove</span><span class="special">()</span> <span class="special">{</span> <span class="identifier">shared_memory_object</span><span class="special">::</span><span class="identifier">remove</span><span class="special">(</span><span class="string">"MySharedMemory"</span><span class="special">);</span> <span class="special">}</span>
 420       <span class="special">~</span><span class="identifier">shm_remove</span><span class="special">(){</span> <span class="identifier">shared_memory_object</span><span class="special">::</span><span class="identifier">remove</span><span class="special">(</span><span class="string">"MySharedMemory"</span><span class="special">);</span> <span class="special">}</span>
 421    <span class="special">}</span> <span class="identifier">remover</span><span class="special">;</span>
 422
 423    <span class="comment">//Create shared memory</span>
 424    <span class="identifier">managed_shared_memory</span> <span class="identifier">segment</span><span class="special">(</span><span class="identifier">create_only</span><span class="special">,</span>
 425                                  <span class="string">"MySharedMemory"</span><span class="special">,</span>  <span class="comment">//segment name</span>
 426                                  <span class="number">65536</span><span class="special">);</span>
 427
 428    <span class="comment">//Create a node_allocator that allocates ints from the managed segment</span>
 429    <span class="comment">//The number of chunks per segment is the default value</span>
 430    <span class="keyword">typedef</span> <span class="identifier">node_allocator</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">,</span> <span class="identifier">managed_shared_memory</span><span class="special">::</span><span class="identifier">segment_manager</span><span class="special">&gt;</span>
 431       <span class="identifier">node_allocator_t</span><span class="special">;</span>
 432    <span class="identifier">node_allocator_t</span> <span class="identifier">allocator_instance</span><span class="special">(</span><span class="identifier">segment</span><span class="special">.</span><span class="identifier">get_segment_manager</span><span class="special">());</span>
 433
 434    <span class="comment">//Create another node_allocator. Since the segment manager address</span>
 435    <span class="comment">//is the same, this node_allocator will be</span>
 436    <span class="comment">//attached to the same pool so "allocator_instance2" can deallocate</span>
 437    <span class="comment">//nodes allocated by "allocator_instance"</span>
 438    <span class="identifier">node_allocator_t</span> <span class="identifier">allocator_instance2</span><span class="special">(</span><span class="identifier">segment</span><span class="special">.</span><span class="identifier">get_segment_manager</span><span class="special">());</span>
 439
 440    <span class="comment">//Create another node_allocator using copy-constructor. This</span>
 441    <span class="comment">//node_allocator will also be attached to the same pool</span>
 442    <span class="identifier">node_allocator_t</span> <span class="identifier">allocator_instance3</span><span class="special">(</span><span class="identifier">allocator_instance2</span><span class="special">);</span>
 443
 444    <span class="comment">//All allocators are equal</span>
 445    <span class="identifier">assert</span><span class="special">(</span><span class="identifier">allocator_instance</span> <span class="special">==</span> <span class="identifier">allocator_instance2</span><span class="special">);</span>
 446    <span class="identifier">assert</span><span class="special">(</span><span class="identifier">allocator_instance2</span> <span class="special">==</span> <span class="identifier">allocator_instance3</span><span class="special">);</span>
 447
 448    <span class="comment">//So memory allocated with one can be deallocated with another</span>
 449    <span class="identifier">allocator_instance2</span><span class="special">.</span><span class="identifier">deallocate</span><span class="special">(</span><span class="identifier">allocator_instance</span><span class="special">.</span><span class="identifier">allocate</span><span class="special">(</span><span class="number">1</span><span class="special">),</span> <span class="number">1</span><span class="special">);</span>
 450    <span class="identifier">allocator_instance3</span><span class="special">.</span><span class="identifier">deallocate</span><span class="special">(</span><span class="identifier">allocator_instance2</span><span class="special">.</span><span class="identifier">allocate</span><span class="special">(</span><span class="number">1</span><span class="special">),</span> <span class="number">1</span><span class="special">);</span>
 451
 452    <span class="comment">//The common pool will be destroyed here, since no allocator is</span>
 453    <span class="comment">//attached to the pool</span>
 454    <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span>
 455 <span class="special">}</span>
 456 </pre>
 457 <p>
 458         </p>
 459 </div>
 460 <div class="section">
 461 <div class="titlepage"><div><div><h4 class="title">
 462 <a name="interprocess.allocators_containers.stl_allocators_segregated_storage.private_node_allocator"></a><a class="link" href="allocators_containers.html#interprocess.allocators_containers.stl_allocators_segregated_storage.private_node_allocator" title="private_node_allocator: a private segregated storage">private_node_allocator:
 463         a private segregated storage</a>
 464 </h4></div></div></div>
 465 <p>
 466           As said, the node_allocator shares a common segregated storage between
 467           node_allocators that allocate objects of the same size and this optimizes
 468           memory usage. However, it needs a unique/named object construction feature
 469           so that this sharing can be possible. Also imposes a synchronization overhead
 470           per node allocation because of this share. Sometimes, the unique object
 471           service is not available (for example, when building index types to implement
 472           the named allocation service itself) or the synchronization overhead is
 473           not acceptable. Many times the programmer wants to make sure that the pool
 474           is destroyed when the allocator is destroyed, to free the memory as soon
 475           as possible.
 476         </p>
 477 <p>
 478           So <span class="bold"><strong>private_node_allocator</strong></span> uses the same
 479           segregated storage as <code class="computeroutput"><span class="identifier">node_allocator</span></code>,
 480           but each <span class="bold"><strong>private_node_allocator</strong></span> has its
 481           own segregated storage pool. No synchronization is used when allocating
 482           nodes, so there is far less overhead for an operation that usually involves
 483           just a few pointer operations when allocating and deallocating a node.
 484         </p>
 485 <p>
 486           <span class="bold"><strong>Equality:</strong></span> Two <code class="computeroutput"><a class="link" href="../boost/interprocess/private_node_allocator.html" title="Class template private_node_allocator">private_node_allocator</a></code>
 487           instances <span class="bold"><strong>never</strong></span> compare equal. Memory
 488           allocated with one allocator <span class="bold"><strong>can't</strong></span> be
 489           deallocated with another one.
 490         </p>
 491 <p>
 492           <span class="bold"><strong>Allocation thread-safety:</strong></span> Allocation and
 493           deallocation are <span class="bold"><strong>not</strong></span> thread-safe.
 494         </p>
 495 <p>
 496           To use <code class="computeroutput"><a class="link" href="../boost/interprocess/private_node_allocator.html" title="Class template private_node_allocator">private_node_allocator</a></code>,
 497           you must include the following header:
 498         </p>
 499 <pre class="programlisting"><span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">interprocess</span><span class="special">/</span><span class="identifier">allocators</span><span class="special">/</span><span class="identifier">private_node_allocator</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
 500 </pre>
 501 <p>
 502           <code class="computeroutput"><a class="link" href="../boost/interprocess/private_node_allocator.html" title="Class template private_node_allocator">private_node_allocator</a></code>
 503           has the following declaration:
 504         </p>
 505 <pre class="programlisting"><span class="keyword">namespace</span> <span class="identifier">boost</span> <span class="special">{</span>
 506 <span class="keyword">namespace</span> <span class="identifier">interprocess</span> <span class="special">{</span>
 507
 508 <span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">,</span> <span class="keyword">class</span> <span class="identifier">SegmentManager</span><span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">NodesPerChunk</span> <span class="special">=</span> <span class="special">...&gt;</span>
 509 <span class="keyword">class</span> <span class="identifier">private_node_allocator</span><span class="special">;</span>
 510
 511 <span class="special">}</span>  <span class="comment">//namespace interprocess {</span>
 512 <span class="special">}</span>  <span class="comment">//namespace boost {</span>
 513 </pre>
 514 <p>
 515           An example using <code class="computeroutput"><a class="link" href="../boost/interprocess/private_node_allocator.html" title="Class template private_node_allocator">private_node_allocator</a></code>:
 516         </p>
 517 <p>
 518 </p>
 519 <pre class="programlisting"><span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">interprocess</span><span class="special">/</span><span class="identifier">managed_shared_memory</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
 520 <span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">interprocess</span><span class="special">/</span><span class="identifier">allocators</span><span class="special">/</span><span class="identifier">private_node_allocator</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
 521 <span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">cassert</span><span class="special">&gt;</span>
 522
 523 <span class="keyword">using</span> <span class="keyword">namespace</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">;</span>
 524
 525 <span class="keyword">int</span> <span class="identifier">main</span> <span class="special">()</span>
 526 <span class="special">{</span>
 527    <span class="comment">//Remove shared memory on construction and destruction</span>
 528    <span class="keyword">struct</span> <span class="identifier">shm_remove</span>
 529    <span class="special">{</span>
 530       <span class="identifier">shm_remove</span><span class="special">()</span> <span class="special">{</span> <span class="identifier">shared_memory_object</span><span class="special">::</span><span class="identifier">remove</span><span class="special">(</span><span class="string">"MySharedMemory"</span><span class="special">);</span> <span class="special">}</span>
 531       <span class="special">~</span><span class="identifier">shm_remove</span><span class="special">(){</span> <span class="identifier">shared_memory_object</span><span class="special">::</span><span class="identifier">remove</span><span class="special">(</span><span class="string">"MySharedMemory"</span><span class="special">);</span> <span class="special">}</span>
 532    <span class="special">}</span>  <span class="identifier">remover</span><span class="special">;</span>
 533
 534    <span class="comment">//Create shared memory</span>
 535    <span class="identifier">managed_shared_memory</span> <span class="identifier">segment</span><span class="special">(</span><span class="identifier">create_only</span><span class="special">,</span>
 536                                  <span class="string">"MySharedMemory"</span><span class="special">,</span>  <span class="comment">//segment name</span>
 537                                  <span class="number">65536</span><span class="special">);</span>
 538
 539    <span class="comment">//Create a private_node_allocator that allocates ints from the managed segment</span>
 540    <span class="comment">//The number of chunks per segment is the default value</span>
 541    <span class="keyword">typedef</span> <span class="identifier">private_node_allocator</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">,</span> <span class="identifier">managed_shared_memory</span><span class="special">::</span><span class="identifier">segment_manager</span><span class="special">&gt;</span>
 542       <span class="identifier">private_node_allocator_t</span><span class="special">;</span>
 543    <span class="identifier">private_node_allocator_t</span> <span class="identifier">allocator_instance</span><span class="special">(</span><span class="identifier">segment</span><span class="special">.</span><span class="identifier">get_segment_manager</span><span class="special">());</span>
 544
 545    <span class="comment">//Create another private_node_allocator.</span>
 546    <span class="identifier">private_node_allocator_t</span> <span class="identifier">allocator_instance2</span><span class="special">(</span><span class="identifier">segment</span><span class="special">.</span><span class="identifier">get_segment_manager</span><span class="special">());</span>
 547
 548    <span class="comment">//Although the segment manager address</span>
 549    <span class="comment">//is the same, this private_node_allocator will have its own pool so</span>
 550    <span class="comment">//"allocator_instance2" CAN'T deallocate nodes allocated by "allocator_instance".</span>
 551    <span class="comment">//"allocator_instance2" is NOT equal to "allocator_instance"</span>
 552    <span class="identifier">assert</span><span class="special">(</span><span class="identifier">allocator_instance</span> <span class="special">!=</span> <span class="identifier">allocator_instance2</span><span class="special">);</span>
 553
 554    <span class="comment">//Create another node_allocator using copy-constructor.</span>
 555    <span class="identifier">private_node_allocator_t</span> <span class="identifier">allocator_instance3</span><span class="special">(</span><span class="identifier">allocator_instance2</span><span class="special">);</span>
 556
 557    <span class="comment">//This allocator is also unequal to allocator_instance2</span>
 558    <span class="identifier">assert</span><span class="special">(</span><span class="identifier">allocator_instance2</span> <span class="special">!=</span> <span class="identifier">allocator_instance3</span><span class="special">);</span>
 559
 560    <span class="comment">//Pools are destroyed with the allocators</span>
 561    <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span>
 562 <span class="special">}</span>
 563 </pre>
 564 <p>
 565         </p>
 566 </div>
 567 <div class="section">
 568 <div class="titlepage"><div><div><h4 class="title">
 569 <a name="interprocess.allocators_containers.stl_allocators_segregated_storage.cached_node_allocator"></a><a class="link" href="allocators_containers.html#interprocess.allocators_containers.stl_allocators_segregated_storage.cached_node_allocator" title="cached_node_allocator: caching nodes to avoid overhead">cached_node_allocator:
 570         caching nodes to avoid overhead</a>
 571 </h4></div></div></div>
 572 <p>
 573           The total node sharing of <code class="computeroutput"><a class="link" href="../boost/interprocess/node_allocator.html" title="Class template node_allocator">node_allocator</a></code>
 574           can impose a high overhead for some applications and the minimal synchronization
 575           overhead of <code class="computeroutput"><a class="link" href="../boost/interprocess/private_node_allocator.html" title="Class template private_node_allocator">private_node_allocator</a></code>
 576           can impose a unacceptable memory waste for other applications.
 577         </p>
 578 <p>
 579           To solve this, <span class="bold"><strong>Boost.Interprocess</strong></span> offers
 580           an allocator, <code class="computeroutput"><a class="link" href="../boost/interprocess/cached_node_allocator.html" title="Class template cached_node_allocator">cached_node_allocator</a></code>,
 581           that allocates nodes from the common pool but caches some of them privately
 582           so that following allocations have no synchronization overhead. When the
 583           cache is full, the allocator returns some cached nodes to the common pool,
 584           and those will be available to other allocators.
 585         </p>
 586 <p>
 587           <span class="bold"><strong>Equality:</strong></span> Two <code class="computeroutput"><a class="link" href="../boost/interprocess/cached_node_allocator.html" title="Class template cached_node_allocator">cached_node_allocator</a></code>
 588           instances constructed with the same segment manager compare equal. If an
 589           instance is created using copy constructor, that instance compares equal
 590           with the original one.
 591         </p>
 592 <p>
 593           <span class="bold"><strong>Allocation thread-safety:</strong></span> Allocation and
 594           deallocation are <span class="bold"><strong>not</strong></span> thread-safe.
 595         </p>
 596 <p>
 597           To use <code class="computeroutput"><a class="link" href="../boost/interprocess/cached_node_allocator.html" title="Class template cached_node_allocator">cached_node_allocator</a></code>,
 598           you must include the following header:
 599         </p>
 600 <pre class="programlisting"><span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">interprocess</span><span class="special">/</span><span class="identifier">allocators</span><span class="special">/</span><span class="identifier">cached_node_allocator</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
 601 </pre>
 602 <p>
 603           <code class="computeroutput"><a class="link" href="../boost/interprocess/cached_node_allocator.html" title="Class template cached_node_allocator">cached_node_allocator</a></code>
 604           has the following declaration:
 605         </p>
 606 <pre class="programlisting"><span class="keyword">namespace</span> <span class="identifier">boost</span> <span class="special">{</span>
 607 <span class="keyword">namespace</span> <span class="identifier">interprocess</span> <span class="special">{</span>
 608
 609 <span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">,</span> <span class="keyword">class</span> <span class="identifier">SegmentManager</span><span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">NodesPerChunk</span> <span class="special">=</span> <span class="special">...&gt;</span>
 610 <span class="keyword">class</span> <span class="identifier">cached_node_allocator</span><span class="special">;</span>
 611
 612 <span class="special">}</span>  <span class="comment">//namespace interprocess {</span>
 613 <span class="special">}</span>  <span class="comment">//namespace boost {</span>
 614 </pre>
 615 <p>
 616           A <code class="computeroutput"><a class="link" href="../boost/interprocess/cached_node_allocator.html" title="Class template cached_node_allocator">cached_node_allocator</a></code>
 617           instance and a <code class="computeroutput"><a class="link" href="../boost/interprocess/node_allocator.html" title="Class template node_allocator">node_allocator</a></code>
 618           instance share the same pool if both instances receive the same template
 619           parameters. This means that nodes returned to the shared pool by one of
 620           them can be reused by the other. Please note that this does not mean that
 621           both allocators compare equal, this is just information for programmers
 622           that want to maximize the use of the pool.
 623         </p>
 624 <p>
 625           <code class="computeroutput"><a class="link" href="../boost/interprocess/cached_node_allocator.html" title="Class template cached_node_allocator">cached_node_allocator</a></code>,
 626           offers additional functions to control the cache (the cache can be controlled
 627           per instance):
 628         </p>
 629 <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
 630 <li class="listitem">
 631               <code class="computeroutput"><span class="keyword">void</span> <span class="identifier">set_max_cached_nodes</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span>
 632               <span class="identifier">n</span><span class="special">)</span></code>:
 633               Sets the maximum cached nodes limit. If cached nodes reach the limit,
 634               some are returned to the shared pool.
 635             </li>
 636 <li class="listitem">
 637               <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">get_max_cached_nodes</span><span class="special">()</span> <span class="keyword">const</span></code>:
 638               Returns the maximum cached nodes limit.
 639             </li>
 640 <li class="listitem">
 641               <code class="computeroutput"><span class="keyword">void</span> <span class="identifier">deallocate_cache</span><span class="special">()</span></code>: Returns the cached nodes to the
 642               shared pool.
 643             </li>
 644 </ul></div>
 645 <p>
 646           An example using <code class="computeroutput"><a class="link" href="../boost/interprocess/cached_node_allocator.html" title="Class template cached_node_allocator">cached_node_allocator</a></code>:
 647         </p>
 648 <p>
 649 </p>
 650 <pre class="programlisting"><span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">interprocess</span><span class="special">/</span><span class="identifier">managed_shared_memory</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
 651 <span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">interprocess</span><span class="special">/</span><span class="identifier">allocators</span><span class="special">/</span><span class="identifier">cached_node_allocator</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
 652 <span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">cassert</span><span class="special">&gt;</span>
 653
 654 <span class="keyword">using</span> <span class="keyword">namespace</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">;</span>
 655
 656 <span class="keyword">int</span> <span class="identifier">main</span> <span class="special">()</span>
 657 <span class="special">{</span>
 658    <span class="comment">//Remove shared memory on construction and destruction</span>
 659    <span class="keyword">struct</span> <span class="identifier">shm_remove</span>
 660    <span class="special">{</span>
 661       <span class="identifier">shm_remove</span><span class="special">()</span> <span class="special">{</span> <span class="identifier">shared_memory_object</span><span class="special">::</span><span class="identifier">remove</span><span class="special">(</span><span class="string">"MySharedMemory"</span><span class="special">);</span> <span class="special">}</span>
 662       <span class="special">~</span><span class="identifier">shm_remove</span><span class="special">(){</span> <span class="identifier">shared_memory_object</span><span class="special">::</span><span class="identifier">remove</span><span class="special">(</span><span class="string">"MySharedMemory"</span><span class="special">);</span> <span class="special">}</span>
 663    <span class="special">}</span> <span class="identifier">remover</span><span class="special">;</span>
 664
 665    <span class="comment">//Create shared memory</span>
 666    <span class="identifier">managed_shared_memory</span> <span class="identifier">segment</span><span class="special">(</span><span class="identifier">create_only</span><span class="special">,</span>
 667                                  <span class="string">"MySharedMemory"</span><span class="special">,</span>  <span class="comment">//segment name</span>
 668                                  <span class="number">65536</span><span class="special">);</span>
 669
 670    <span class="comment">//Create a cached_node_allocator that allocates ints from the managed segment</span>
 671    <span class="comment">//The number of chunks per segment is the default value</span>
 672    <span class="keyword">typedef</span> <span class="identifier">cached_node_allocator</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">,</span> <span class="identifier">managed_shared_memory</span><span class="special">::</span><span class="identifier">segment_manager</span><span class="special">&gt;</span>
 673       <span class="identifier">cached_node_allocator_t</span><span class="special">;</span>
 674    <span class="identifier">cached_node_allocator_t</span> <span class="identifier">allocator_instance</span><span class="special">(</span><span class="identifier">segment</span><span class="special">.</span><span class="identifier">get_segment_manager</span><span class="special">());</span>
 675
 676    <span class="comment">//The max cached nodes are configurable per instance</span>
 677    <span class="identifier">allocator_instance</span><span class="special">.</span><span class="identifier">set_max_cached_nodes</span><span class="special">(</span><span class="number">3</span><span class="special">);</span>
 678
 679    <span class="comment">//Create another cached_node_allocator. Since the segment manager address</span>
 680    <span class="comment">//is the same, this cached_node_allocator will be</span>
 681    <span class="comment">//attached to the same pool so "allocator_instance2" can deallocate</span>
 682    <span class="comment">//nodes allocated by "allocator_instance"</span>
 683    <span class="identifier">cached_node_allocator_t</span> <span class="identifier">allocator_instance2</span><span class="special">(</span><span class="identifier">segment</span><span class="special">.</span><span class="identifier">get_segment_manager</span><span class="special">());</span>
 684
 685    <span class="comment">//The max cached nodes are configurable per instance</span>
 686    <span class="identifier">allocator_instance2</span><span class="special">.</span><span class="identifier">set_max_cached_nodes</span><span class="special">(</span><span class="number">5</span><span class="special">);</span>
 687
 688    <span class="comment">//Create another cached_node_allocator using copy-constructor. This</span>
 689    <span class="comment">//cached_node_allocator will also be attached to the same pool</span>
 690    <span class="identifier">cached_node_allocator_t</span> <span class="identifier">allocator_instance3</span><span class="special">(</span><span class="identifier">allocator_instance2</span><span class="special">);</span>
 691
 692    <span class="comment">//We can clear the cache</span>
 693    <span class="identifier">allocator_instance3</span><span class="special">.</span><span class="identifier">deallocate_cache</span><span class="special">();</span>
 694
 695    <span class="comment">//All allocators are equal</span>
 696    <span class="identifier">assert</span><span class="special">(</span><span class="identifier">allocator_instance</span> <span class="special">==</span> <span class="identifier">allocator_instance2</span><span class="special">);</span>
 697    <span class="identifier">assert</span><span class="special">(</span><span class="identifier">allocator_instance2</span> <span class="special">==</span> <span class="identifier">allocator_instance3</span><span class="special">);</span>
 698
 699    <span class="comment">//So memory allocated with one can be deallocated with another</span>
 700    <span class="identifier">allocator_instance2</span><span class="special">.</span><span class="identifier">deallocate</span><span class="special">(</span><span class="identifier">allocator_instance</span><span class="special">.</span><span class="identifier">allocate</span><span class="special">(</span><span class="number">1</span><span class="special">),</span> <span class="number">1</span><span class="special">);</span>
 701    <span class="identifier">allocator_instance3</span><span class="special">.</span><span class="identifier">deallocate</span><span class="special">(</span><span class="identifier">allocator_instance2</span><span class="special">.</span><span class="identifier">allocate</span><span class="special">(</span><span class="number">1</span><span class="special">),</span> <span class="number">1</span><span class="special">);</span>
 702
 703    <span class="comment">//The common pool will be destroyed here, since no allocator is</span>
 704    <span class="comment">//attached to the pool</span>
 705    <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span>
 706 <span class="special">}</span>
 707 </pre>
 708 <p>
 709         </p>
 710 </div>
 711 </div>
 712 <div class="section">
 713 <div class="titlepage"><div><div><h3 class="title">
 714 <a name="interprocess.allocators_containers.stl_allocators_adaptive"></a><a class="link" href="allocators_containers.html#interprocess.allocators_containers.stl_allocators_adaptive" title="Adaptive pool node allocators">Adaptive
 715       pool node allocators</a>
 716 </h3></div></div></div>
 717 <div class="toc"><dl class="toc">
 718 <dt><span class="section"><a href="allocators_containers.html#interprocess.allocators_containers.stl_allocators_adaptive.adaptive_allocators_common">Additional
 719         parameters and functions of adaptive pool node allocators</a></span></dt>
 720 <dt><span class="section"><a href="allocators_containers.html#interprocess.allocators_containers.stl_allocators_adaptive.adaptive_pool">adaptive_pool:
 721         a process-shared adaptive pool</a></span></dt>
 722 <dt><span class="section"><a href="allocators_containers.html#interprocess.allocators_containers.stl_allocators_adaptive.private_adaptive_pool">private_adaptive_pool:
 723         a private adaptive pool</a></span></dt>
 724 <dt><span class="section"><a href="allocators_containers.html#interprocess.allocators_containers.stl_allocators_adaptive.cached_adaptive_pool">cached_adaptive_pool:
 725         Avoiding synchronization overhead</a></span></dt>
 726 </dl></div>
 727 <p>
 728         Node allocators based on simple segregated storage algorithm are both space-efficient
 729         and fast but they have a problem: they only can grow. Every allocated node
 730         avoids any payload to store additional data and that leads to the following
 731         limitation: when a node is deallocated, it's stored in a free list of nodes
 732         but memory is not returned to the segment manager so a deallocated node can
 733         be only reused by other containers using the same node pool.
 734       </p>
 735 <p>
 736         This behaviour can be problematic if several containers use <code class="computeroutput"><a class="link" href="../boost/interprocess/node_allocator.html" title="Class template node_allocator">boost::interprocess::node_allocator</a></code>
 737         to temporarily allocate a lot of objects but they end storing a few of them:
 738         the node pool will be full of nodes that won't be reused wasting memory from
 739         the segment.
 740       </p>
 741 <p>
 742         Adaptive pool based allocators trade some space (the overhead can be as low
 743         as 1%) and performance (acceptable for many applications) with the ability
 744         to return free chunks of nodes to the memory segment, so that they can be
 745         used by any other container or managed object construction. To know the details
 746         of the implementation of of "adaptive pools" see the <a class="link" href="architecture.html#interprocess.architecture.allocators_containers.implementation_adaptive_pools" title="Implementation of Boost.Interprocess adaptive pools">Implementation
 747         of <span class="bold"><strong>Boost.Intrusive</strong></span> adaptive pools</a>
 748         section.
 749       </p>
 750 <p>
 751         Like with segregated storage based node allocators, Boost.Interprocess offers
 752         3 new allocators: <code class="computeroutput"><a class="link" href="../boost/interprocess/adaptive_pool.html" title="Class template adaptive_pool">adaptive_pool</a></code>,
 753         <code class="computeroutput"><a class="link" href="../boost/interprocess/private_adaptive_pool.html" title="Class template private_adaptive_pool">private_adaptive_pool</a></code>,
 754         <code class="computeroutput"><a class="link" href="../boost/interprocess/cached_adaptive_pool.html" title="Class template cached_adaptive_pool">cached_adaptive_pool</a></code>.
 755       </p>
 756 <div class="section">
 757 <div class="titlepage"><div><div><h4 class="title">
 758 <a name="interprocess.allocators_containers.stl_allocators_adaptive.adaptive_allocators_common"></a><a class="link" href="allocators_containers.html#interprocess.allocators_containers.stl_allocators_adaptive.adaptive_allocators_common" title="Additional parameters and functions of adaptive pool node allocators">Additional
 759         parameters and functions of adaptive pool node allocators</a>
 760 </h4></div></div></div>
 761 <p>
 762           <code class="computeroutput"><a class="link" href="../boost/interprocess/adaptive_pool.html" title="Class template adaptive_pool">adaptive_pool</a></code>,
 763           <code class="computeroutput"><a class="link" href="../boost/interprocess/private_adaptive_pool.html" title="Class template private_adaptive_pool">private_adaptive_pool</a></code>
 764           and <code class="computeroutput"><a class="link" href="../boost/interprocess/cached_adaptive_pool.html" title="Class template cached_adaptive_pool">cached_adaptive_pool</a></code>
 765           implement the standard allocator interface and the functions explained
 766           in the <a class="link" href="allocators_containers.html#interprocess.allocators_containers.allocator_introduction.allocator_properties" title="Properties of Boost.Interprocess allocators">Properties
 767           of Boost.Interprocess allocators</a>.
 768         </p>
 769 <p>
 770           All these allocators are templatized by 4 parameters:
 771         </p>
 772 <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
 773 <li class="listitem">
 774               <code class="computeroutput"><span class="keyword">class</span> <span class="identifier">T</span></code>:
 775               The type to be allocated.
 776             </li>
 777 <li class="listitem">
 778               <code class="computeroutput"><span class="keyword">class</span> <span class="identifier">SegmentManager</span></code>:
 779               The type of the segment manager that will be passed in the constructor.
 780             </li>
 781 <li class="listitem">
 782               <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">NodesPerChunk</span></code>:
 783               The number of nodes that a memory chunk will contain. This value will
 784               define the size of the memory the pool will request to the segment
 785               manager when the pool runs out of nodes. This parameter has a default
 786               value.
 787             </li>
 788 <li class="listitem">
 789               <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">MaxFreeChunks</span></code>:
 790               The maximum number of free chunks that the pool will hold. If this
 791               limit is reached the pool returns the chunks to the segment manager.
 792               This parameter has a default value.
 793             </li>
 794 </ul></div>
 795 <p>
 796           These allocators also offer the <code class="computeroutput"><span class="identifier">deallocate_free_chunks</span><span class="special">()</span></code> function. This function will traverse
 797           all the memory chunks of the pool and will return to the managed memory
 798           segment the free chunks of memory. This function is much faster than for
 799           segregated storage allocators, because the adaptive pool algorithm offers
 800           constant-time access to free chunks.
 801         </p>
 802 </div>
 803 <div class="section">
 804 <div class="titlepage"><div><div><h4 class="title">
 805 <a name="interprocess.allocators_containers.stl_allocators_adaptive.adaptive_pool"></a><a class="link" href="allocators_containers.html#interprocess.allocators_containers.stl_allocators_adaptive.adaptive_pool" title="adaptive_pool: a process-shared adaptive pool">adaptive_pool:
 806         a process-shared adaptive pool</a>
 807 </h4></div></div></div>
 808 <p>
 809           Just like <code class="computeroutput"><a class="link" href="../boost/interprocess/node_allocator.html" title="Class template node_allocator">node_allocator</a></code>
 810           a global, process-thread pool is used for each node size. In the initialization,
 811           <code class="computeroutput"><a class="link" href="../boost/interprocess/adaptive_pool.html" title="Class template adaptive_pool">adaptive_pool</a></code>
 812           searches the pool in the segment. If it is not preset, it builds one. The
 813           adaptive pool, is created using a unique name. The adaptive pool it is
 814           also shared between all node_allocators that allocate objects of the same
 815           size, for example, <span class="bold"><strong>adaptive_pool&lt;uint32&gt;</strong></span>
 816           and <span class="bold"><strong>adaptive_pool&lt;float32&gt;</strong></span>.
 817         </p>
 818 <p>
 819           The common adaptive pool is destroyed when all the allocators attached
 820           to the pool are destroyed.
 821         </p>
 822 <p>
 823           <span class="bold"><strong>Equality:</strong></span> Two <code class="computeroutput"><a class="link" href="../boost/interprocess/adaptive_pool.html" title="Class template adaptive_pool">adaptive_pool</a></code>
 824           instances constructed with the same segment manager compare equal. If an
 825           instance is created using copy constructor, that instance compares equal
 826           with the original one.
 827         </p>
 828 <p>
 829           <span class="bold"><strong>Allocation thread-safety:</strong></span> Allocation and
 830           deallocation are implemented as calls to the shared pool. The shared pool
 831           offers the same synchronization guarantees as the segment manager.
 832         </p>
 833 <p>
 834           To use <code class="computeroutput"><a class="link" href="../boost/interprocess/adaptive_pool.html" title="Class template adaptive_pool">adaptive_pool</a></code>,
 835           you must include the following header:
 836         </p>
 837 <pre class="programlisting"><span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">interprocess</span><span class="special">/</span><span class="identifier">allocators</span><span class="special">/</span><span class="identifier">adaptive_pool</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
 838 </pre>
 839 <p>
 840           <code class="computeroutput"><a class="link" href="../boost/interprocess/adaptive_pool.html" title="Class template adaptive_pool">adaptive_pool</a></code>
 841           has the following declaration:
 842         </p>
 843 <pre class="programlisting"><span class="keyword">namespace</span> <span class="identifier">boost</span> <span class="special">{</span>
 844 <span class="keyword">namespace</span> <span class="identifier">interprocess</span> <span class="special">{</span>
 845
 846 <span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">,</span> <span class="keyword">class</span> <span class="identifier">SegmentManager</span><span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">NodesPerChunk</span> <span class="special">=</span> <span class="special">...,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">MaxFreeChunks</span> <span class="special">=</span> <span class="special">...&gt;</span>
 847 <span class="keyword">class</span> <span class="identifier">adaptive_pool</span><span class="special">;</span>
 848
 849 <span class="special">}</span>  <span class="comment">//namespace interprocess {</span>
 850 <span class="special">}</span>  <span class="comment">//namespace boost {</span>
 851 </pre>
 852 <p>
 853           An example using <code class="computeroutput"><a class="link" href="../boost/interprocess/adaptive_pool.html" title="Class template adaptive_pool">adaptive_pool</a></code>:
 854         </p>
 855 <p>
 856 </p>
 857 <pre class="programlisting"><span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">interprocess</span><span class="special">/</span><span class="identifier">managed_shared_memory</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
 858 <span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">interprocess</span><span class="special">/</span><span class="identifier">allocators</span><span class="special">/</span><span class="identifier">adaptive_pool</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
 859 <span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">cassert</span><span class="special">&gt;</span>
 860
 861 <span class="keyword">using</span> <span class="keyword">namespace</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">;</span>
 862
 863 <span class="keyword">int</span> <span class="identifier">main</span> <span class="special">()</span>
 864 <span class="special">{</span>
 865    <span class="comment">//Remove shared memory on construction and destruction</span>
 866    <span class="keyword">struct</span> <span class="identifier">shm_remove</span>
 867    <span class="special">{</span>
 868       <span class="identifier">shm_remove</span><span class="special">()</span> <span class="special">{</span> <span class="identifier">shared_memory_object</span><span class="special">::</span><span class="identifier">remove</span><span class="special">(</span><span class="string">"MySharedMemory"</span><span class="special">);</span> <span class="special">}</span>
 869       <span class="special">~</span><span class="identifier">shm_remove</span><span class="special">(){</span> <span class="identifier">shared_memory_object</span><span class="special">::</span><span class="identifier">remove</span><span class="special">(</span><span class="string">"MySharedMemory"</span><span class="special">);</span> <span class="special">}</span>
 870    <span class="special">}</span> <span class="identifier">remover</span><span class="special">;</span>
 871
 872    <span class="comment">//Create shared memory</span>
 873    <span class="identifier">managed_shared_memory</span> <span class="identifier">segment</span><span class="special">(</span><span class="identifier">create_only</span><span class="special">,</span>
 874                                  <span class="string">"MySharedMemory"</span><span class="special">,</span>  <span class="comment">//segment name</span>
 875                                  <span class="number">65536</span><span class="special">);</span>
 876
 877    <span class="comment">//Create a adaptive_pool that allocates ints from the managed segment</span>
 878    <span class="comment">//The number of chunks per segment is the default value</span>
 879    <span class="keyword">typedef</span> <span class="identifier">adaptive_pool</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">,</span> <span class="identifier">managed_shared_memory</span><span class="special">::</span><span class="identifier">segment_manager</span><span class="special">&gt;</span>
 880       <span class="identifier">adaptive_pool_t</span><span class="special">;</span>
 881    <span class="identifier">adaptive_pool_t</span> <span class="identifier">allocator_instance</span><span class="special">(</span><span class="identifier">segment</span><span class="special">.</span><span class="identifier">get_segment_manager</span><span class="special">());</span>
 882
 883    <span class="comment">//Create another adaptive_pool. Since the segment manager address</span>
 884    <span class="comment">//is the same, this adaptive_pool will be</span>
 885    <span class="comment">//attached to the same pool so "allocator_instance2" can deallocate</span>
 886    <span class="comment">//nodes allocated by "allocator_instance"</span>
 887    <span class="identifier">adaptive_pool_t</span> <span class="identifier">allocator_instance2</span><span class="special">(</span><span class="identifier">segment</span><span class="special">.</span><span class="identifier">get_segment_manager</span><span class="special">());</span>
 888
 889    <span class="comment">//Create another adaptive_pool using copy-constructor. This</span>
 890    <span class="comment">//adaptive_pool will also be attached to the same pool</span>
 891    <span class="identifier">adaptive_pool_t</span> <span class="identifier">allocator_instance3</span><span class="special">(</span><span class="identifier">allocator_instance2</span><span class="special">);</span>
 892
 893    <span class="comment">//All allocators are equal</span>
 894    <span class="identifier">assert</span><span class="special">(</span><span class="identifier">allocator_instance</span> <span class="special">==</span> <span class="identifier">allocator_instance2</span><span class="special">);</span>
 895    <span class="identifier">assert</span><span class="special">(</span><span class="identifier">allocator_instance2</span> <span class="special">==</span> <span class="identifier">allocator_instance3</span><span class="special">);</span>
 896
 897    <span class="comment">//So memory allocated with one can be deallocated with another</span>
 898    <span class="identifier">allocator_instance2</span><span class="special">.</span><span class="identifier">deallocate</span><span class="special">(</span><span class="identifier">allocator_instance</span><span class="special">.</span><span class="identifier">allocate</span><span class="special">(</span><span class="number">1</span><span class="special">),</span> <span class="number">1</span><span class="special">);</span>
 899    <span class="identifier">allocator_instance3</span><span class="special">.</span><span class="identifier">deallocate</span><span class="special">(</span><span class="identifier">allocator_instance2</span><span class="special">.</span><span class="identifier">allocate</span><span class="special">(</span><span class="number">1</span><span class="special">),</span> <span class="number">1</span><span class="special">);</span>
 900
 901    <span class="comment">//The common pool will be destroyed here, since no allocator is</span>
 902    <span class="comment">//attached to the pool</span>
 903    <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span>
 904 <span class="special">}</span>
 905 </pre>
 906 <p>
 907         </p>
 908 </div>
 909 <div class="section">
 910 <div class="titlepage"><div><div><h4 class="title">
 911 <a name="interprocess.allocators_containers.stl_allocators_adaptive.private_adaptive_pool"></a><a class="link" href="allocators_containers.html#interprocess.allocators_containers.stl_allocators_adaptive.private_adaptive_pool" title="private_adaptive_pool: a private adaptive pool">private_adaptive_pool:
 912         a private adaptive pool</a>
 913 </h4></div></div></div>
 914 <p>
 915           Just like <code class="computeroutput"><a class="link" href="../boost/interprocess/private_node_allocator.html" title="Class template private_node_allocator">private_node_allocator</a></code>
 916           owns a private segregated storage pool, <code class="computeroutput"><a class="link" href="../boost/interprocess/private_adaptive_pool.html" title="Class template private_adaptive_pool">private_adaptive_pool</a></code>
 917           owns its own adaptive pool. If the user wants to avoid the excessive node
 918           allocation synchronization overhead in a container <code class="computeroutput"><a class="link" href="../boost/interprocess/private_adaptive_pool.html" title="Class template private_adaptive_pool">private_adaptive_pool</a></code>
 919           is a good choice.
 920         </p>
 921 <p>
 922           <span class="bold"><strong>Equality:</strong></span> Two <code class="computeroutput"><a class="link" href="../boost/interprocess/private_adaptive_pool.html" title="Class template private_adaptive_pool">private_adaptive_pool</a></code>
 923           instances <span class="bold"><strong>never</strong></span> compare equal. Memory
 924           allocated with one allocator <span class="bold"><strong>can't</strong></span> be
 925           deallocated with another one.
 926         </p>
 927 <p>
 928           <span class="bold"><strong>Allocation thread-safety:</strong></span> Allocation and
 929           deallocation are <span class="bold"><strong>not</strong></span> thread-safe.
 930         </p>
 931 <p>
 932           To use <code class="computeroutput"><a class="link" href="../boost/interprocess/private_adaptive_pool.html" title="Class template private_adaptive_pool">private_adaptive_pool</a></code>,
 933           you must include the following header:
 934         </p>
 935 <pre class="programlisting"><span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">interprocess</span><span class="special">/</span><span class="identifier">allocators</span><span class="special">/</span><span class="identifier">private_adaptive_pool</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
 936 </pre>
 937 <p>
 938           <code class="computeroutput"><a class="link" href="../boost/interprocess/private_adaptive_pool.html" title="Class template private_adaptive_pool">private_adaptive_pool</a></code>
 939           has the following declaration:
 940         </p>
 941 <pre class="programlisting"><span class="keyword">namespace</span> <span class="identifier">boost</span> <span class="special">{</span>
 942 <span class="keyword">namespace</span> <span class="identifier">interprocess</span> <span class="special">{</span>
 943
 944 <span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">,</span> <span class="keyword">class</span> <span class="identifier">SegmentManager</span><span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">NodesPerChunk</span> <span class="special">=</span> <span class="special">...,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">MaxFreeChunks</span> <span class="special">=</span> <span class="special">...&gt;</span>
 945 <span class="keyword">class</span> <span class="identifier">private_adaptive_pool</span><span class="special">;</span>
 946
 947 <span class="special">}</span>  <span class="comment">//namespace interprocess {</span>
 948 <span class="special">}</span>  <span class="comment">//namespace boost {</span>
 949 </pre>
 950 <p>
 951           An example using <code class="computeroutput"><a class="link" href="../boost/interprocess/private_adaptive_pool.html" title="Class template private_adaptive_pool">private_adaptive_pool</a></code>:
 952         </p>
 953 <p>
 954 </p>
 955 <pre class="programlisting"><span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">interprocess</span><span class="special">/</span><span class="identifier">managed_shared_memory</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
 956 <span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">interprocess</span><span class="special">/</span><span class="identifier">allocators</span><span class="special">/</span><span class="identifier">private_adaptive_pool</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
 957 <span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">cassert</span><span class="special">&gt;</span>
 958
 959 <span class="keyword">using</span> <span class="keyword">namespace</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">;</span>
 960
 961 <span class="keyword">int</span> <span class="identifier">main</span> <span class="special">()</span>
 962 <span class="special">{</span>
 963    <span class="comment">//Remove shared memory on construction and destruction</span>
 964    <span class="keyword">struct</span> <span class="identifier">shm_remove</span>
 965    <span class="special">{</span>
 966       <span class="identifier">shm_remove</span><span class="special">()</span> <span class="special">{</span> <span class="identifier">shared_memory_object</span><span class="special">::</span><span class="identifier">remove</span><span class="special">(</span><span class="string">"MySharedMemory"</span><span class="special">);</span> <span class="special">}</span>
 967       <span class="special">~</span><span class="identifier">shm_remove</span><span class="special">(){</span> <span class="identifier">shared_memory_object</span><span class="special">::</span><span class="identifier">remove</span><span class="special">(</span><span class="string">"MySharedMemory"</span><span class="special">);</span> <span class="special">}</span>
 968    <span class="special">}</span> <span class="identifier">remover</span><span class="special">;</span>
 969
 970    <span class="comment">//Create shared memory</span>
 971    <span class="identifier">managed_shared_memory</span> <span class="identifier">segment</span><span class="special">(</span><span class="identifier">create_only</span><span class="special">,</span>
 972                                  <span class="string">"MySharedMemory"</span><span class="special">,</span>  <span class="comment">//segment name</span>
 973                                  <span class="number">65536</span><span class="special">);</span>
 974
 975    <span class="comment">//Create a private_adaptive_pool that allocates ints from the managed segment</span>
 976    <span class="comment">//The number of chunks per segment is the default value</span>
 977    <span class="keyword">typedef</span> <span class="identifier">private_adaptive_pool</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">,</span> <span class="identifier">managed_shared_memory</span><span class="special">::</span><span class="identifier">segment_manager</span><span class="special">&gt;</span>
 978          <span class="identifier">private_adaptive_pool_t</span><span class="special">;</span>
 979    <span class="identifier">private_adaptive_pool_t</span> <span class="identifier">allocator_instance</span><span class="special">(</span><span class="identifier">segment</span><span class="special">.</span><span class="identifier">get_segment_manager</span><span class="special">());</span>
 980
 981    <span class="comment">//Create another private_adaptive_pool.</span>
 982    <span class="identifier">private_adaptive_pool_t</span> <span class="identifier">allocator_instance2</span><span class="special">(</span><span class="identifier">segment</span><span class="special">.</span><span class="identifier">get_segment_manager</span><span class="special">());</span>
 983
 984    <span class="comment">//Although the segment manager address</span>
 985    <span class="comment">//is the same, this private_adaptive_pool will have its own pool so</span>
 986    <span class="comment">//"allocator_instance2" CAN'T deallocate nodes allocated by "allocator_instance".</span>
 987    <span class="comment">//"allocator_instance2" is NOT equal to "allocator_instance"</span>
 988    <span class="identifier">assert</span><span class="special">(</span><span class="identifier">allocator_instance</span> <span class="special">!=</span> <span class="identifier">allocator_instance2</span><span class="special">);</span>
 989
 990    <span class="comment">//Create another adaptive_pool using copy-constructor.</span>
 991    <span class="identifier">private_adaptive_pool_t</span> <span class="identifier">allocator_instance3</span><span class="special">(</span><span class="identifier">allocator_instance2</span><span class="special">);</span>
 992
 993    <span class="comment">//This allocator is also unequal to allocator_instance2</span>
 994    <span class="identifier">assert</span><span class="special">(</span><span class="identifier">allocator_instance2</span> <span class="special">!=</span> <span class="identifier">allocator_instance3</span><span class="special">);</span>
 995
 996    <span class="comment">//Pools are destroyed with the allocators</span>
 997    <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span>
 998 <span class="special">}</span>
 999 </pre>
1000 <p>
1001         </p>
1002 </div>
1003 <div class="section">
1004 <div class="titlepage"><div><div><h4 class="title">
1005 <a name="interprocess.allocators_containers.stl_allocators_adaptive.cached_adaptive_pool"></a><a class="link" href="allocators_containers.html#interprocess.allocators_containers.stl_allocators_adaptive.cached_adaptive_pool" title="cached_adaptive_pool: Avoiding synchronization overhead">cached_adaptive_pool:
1006         Avoiding synchronization overhead</a>
1007 </h4></div></div></div>
1008 <p>
1009           Adaptive pools have also a cached version. In this allocator the allocator
1010           caches some nodes to avoid the synchronization and bookkeeping overhead
1011           of the shared adaptive pool. <code class="computeroutput"><a class="link" href="../boost/interprocess/cached_adaptive_pool.html" title="Class template cached_adaptive_pool">cached_adaptive_pool</a></code>
1012           allocates nodes from the common adaptive pool but caches some of them privately
1013           so that following allocations have no synchronization overhead. When the
1014           cache is full, the allocator returns some cached nodes to the common pool,
1015           and those will be available to other <code class="computeroutput"><a class="link" href="../boost/interprocess/cached_adaptive_pool.html" title="Class template cached_adaptive_pool">cached_adaptive_pools</a></code>
1016           or <code class="computeroutput"><a class="link" href="../boost/interprocess/adaptive_pool.html" title="Class template adaptive_pool">adaptive_pools</a></code>
1017           of the same managed segment.
1018         </p>
1019 <p>
1020           <span class="bold"><strong>Equality:</strong></span> Two <code class="computeroutput"><a class="link" href="../boost/interprocess/cached_adaptive_pool.html" title="Class template cached_adaptive_pool">cached_adaptive_pool</a></code>
1021           instances constructed with the same segment manager compare equal. If an
1022           instance is created using copy constructor, that instance compares equal
1023           with the original one.
1024         </p>
1025 <p>
1026           <span class="bold"><strong>Allocation thread-safety:</strong></span> Allocation and
1027           deallocation are <span class="bold"><strong>not</strong></span> thread-safe.
1028         </p>
1029 <p>
1030           To use <code class="computeroutput"><a class="link" href="../boost/interprocess/cached_adaptive_pool.html" title="Class template cached_adaptive_pool">cached_adaptive_pool</a></code>,
1031           you must include the following header:
1032         </p>
1033 <pre class="programlisting"><span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">interprocess</span><span class="special">/</span><span class="identifier">allocators</span><span class="special">/</span><span class="identifier">cached_adaptive_pool</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
1034 </pre>
1035 <p>
1036           <code class="computeroutput"><a class="link" href="../boost/interprocess/cached_adaptive_pool.html" title="Class template cached_adaptive_pool">cached_adaptive_pool</a></code>
1037           has the following declaration:
1038         </p>
1039 <pre class="programlisting"><span class="keyword">namespace</span> <span class="identifier">boost</span> <span class="special">{</span>
1040 <span class="keyword">namespace</span> <span class="identifier">interprocess</span> <span class="special">{</span>
1041
1042 <span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">,</span> <span class="keyword">class</span> <span class="identifier">SegmentManager</span><span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">NodesPerChunk</span> <span class="special">=</span> <span class="special">...,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">MaxFreeNodes</span> <span class="special">=</span> <span class="special">...&gt;</span>
1043 <span class="keyword">class</span> <span class="identifier">cached_adaptive_pool</span><span class="special">;</span>
1044
1045 <span class="special">}</span>  <span class="comment">//namespace interprocess {</span>
1046 <span class="special">}</span>  <span class="comment">//namespace boost {</span>
1047 </pre>
1048 <p>
1049           A <code class="computeroutput"><a class="link" href="../boost/interprocess/cached_adaptive_pool.html" title="Class template cached_adaptive_pool">cached_adaptive_pool</a></code>
1050           instance and an <code class="computeroutput"><a class="link" href="../boost/interprocess/adaptive_pool.html" title="Class template adaptive_pool">adaptive_pool</a></code>
1051           instance share the same pool if both instances receive the same template
1052           parameters. This means that nodes returned to the shared pool by one of
1053           them can be reused by the other. Please note that this does not mean that
1054           both allocators compare equal, this is just information for programmers
1055           that want to maximize the use of the pool.
1056         </p>
1057 <p>
1058           <code class="computeroutput"><a class="link" href="../boost/interprocess/cached_adaptive_pool.html" title="Class template cached_adaptive_pool">cached_adaptive_pool</a></code>,
1059           offers additional functions to control the cache (the cache can be controlled
1060           per instance):
1061         </p>
1062 <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
1063 <li class="listitem">
1064               <code class="computeroutput"><span class="keyword">void</span> <span class="identifier">set_max_cached_nodes</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span>
1065               <span class="identifier">n</span><span class="special">)</span></code>:
1066               Sets the maximum cached nodes limit. If cached nodes reach the limit,
1067               some are returned to the shared pool.
1068             </li>
1069 <li class="listitem">
1070               <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">get_max_cached_nodes</span><span class="special">()</span> <span class="keyword">const</span></code>:
1071               Returns the maximum cached nodes limit.
1072             </li>
1073 <li class="listitem">
1074               <code class="computeroutput"><span class="keyword">void</span> <span class="identifier">deallocate_cache</span><span class="special">()</span></code>: Returns the cached nodes to the
1075               shared pool.
1076             </li>
1077 </ul></div>
1078 <p>
1079           An example using <code class="computeroutput"><a class="link" href="../boost/interprocess/cached_adaptive_pool.html" title="Class template cached_adaptive_pool">cached_adaptive_pool</a></code>:
1080         </p>
1081 <p>
1082 </p>
1083 <pre class="programlisting"><span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">interprocess</span><span class="special">/</span><span class="identifier">managed_shared_memory</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
1084 <span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">interprocess</span><span class="special">/</span><span class="identifier">allocators</span><span class="special">/</span><span class="identifier">cached_adaptive_pool</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
1085 <span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">cassert</span><span class="special">&gt;</span>
1086
1087 <span class="keyword">using</span> <span class="keyword">namespace</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">;</span>
1088
1089 <span class="keyword">int</span> <span class="identifier">main</span> <span class="special">()</span>
1090 <span class="special">{</span>
1091    <span class="comment">//Remove shared memory on construction and destruction</span>
1092    <span class="keyword">struct</span> <span class="identifier">shm_remove</span>
1093    <span class="special">{</span>
1094       <span class="identifier">shm_remove</span><span class="special">()</span> <span class="special">{</span> <span class="identifier">shared_memory_object</span><span class="special">::</span><span class="identifier">remove</span><span class="special">(</span><span class="string">"MySharedMemory"</span><span class="special">);</span> <span class="special">}</span>
1095       <span class="special">~</span><span class="identifier">shm_remove</span><span class="special">(){</span> <span class="identifier">shared_memory_object</span><span class="special">::</span><span class="identifier">remove</span><span class="special">(</span><span class="string">"MySharedMemory"</span><span class="special">);</span> <span class="special">}</span>
1096    <span class="special">}</span> <span class="identifier">remover</span><span class="special">;</span>
1097
1098    <span class="comment">//Create shared memory</span>
1099    <span class="identifier">managed_shared_memory</span> <span class="identifier">segment</span><span class="special">(</span><span class="identifier">create_only</span><span class="special">,</span>
1100                                  <span class="string">"MySharedMemory"</span><span class="special">,</span>  <span class="comment">//segment name</span>
1101                                  <span class="number">65536</span><span class="special">);</span>
1102
1103    <span class="comment">//Create a cached_adaptive_pool that allocates ints from the managed segment</span>
1104    <span class="comment">//The number of chunks per segment is the default value</span>
1105    <span class="keyword">typedef</span> <span class="identifier">cached_adaptive_pool</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">,</span> <span class="identifier">managed_shared_memory</span><span class="special">::</span><span class="identifier">segment_manager</span><span class="special">&gt;</span>
1106       <span class="identifier">cached_adaptive_pool_t</span><span class="special">;</span>
1107    <span class="identifier">cached_adaptive_pool_t</span> <span class="identifier">allocator_instance</span><span class="special">(</span><span class="identifier">segment</span><span class="special">.</span><span class="identifier">get_segment_manager</span><span class="special">());</span>
1108
1109    <span class="comment">//The max cached nodes are configurable per instance</span>
1110    <span class="identifier">allocator_instance</span><span class="special">.</span><span class="identifier">set_max_cached_nodes</span><span class="special">(</span><span class="number">3</span><span class="special">);</span>
1111
1112    <span class="comment">//Create another cached_adaptive_pool. Since the segment manager address</span>
1113    <span class="comment">//is the same, this cached_adaptive_pool will be</span>
1114    <span class="comment">//attached to the same pool so "allocator_instance2" can deallocate</span>
1115    <span class="comment">//nodes allocated by "allocator_instance"</span>
1116    <span class="identifier">cached_adaptive_pool_t</span> <span class="identifier">allocator_instance2</span><span class="special">(</span><span class="identifier">segment</span><span class="special">.</span><span class="identifier">get_segment_manager</span><span class="special">());</span>
1117
1118    <span class="comment">//The max cached nodes are configurable per instance</span>
1119    <span class="identifier">allocator_instance2</span><span class="special">.</span><span class="identifier">set_max_cached_nodes</span><span class="special">(</span><span class="number">5</span><span class="special">);</span>
1120
1121    <span class="comment">//Create another cached_adaptive_pool using copy-constructor. This</span>
1122    <span class="comment">//cached_adaptive_pool will also be attached to the same pool</span>
1123    <span class="identifier">cached_adaptive_pool_t</span> <span class="identifier">allocator_instance3</span><span class="special">(</span><span class="identifier">allocator_instance2</span><span class="special">);</span>
1124
1125    <span class="comment">//We can clear the cache</span>
1126    <span class="identifier">allocator_instance3</span><span class="special">.</span><span class="identifier">deallocate_cache</span><span class="special">();</span>
1127
1128    <span class="comment">//All allocators are equal</span>
1129    <span class="identifier">assert</span><span class="special">(</span><span class="identifier">allocator_instance</span> <span class="special">==</span> <span class="identifier">allocator_instance2</span><span class="special">);</span>
1130    <span class="identifier">assert</span><span class="special">(</span><span class="identifier">allocator_instance2</span> <span class="special">==</span> <span class="identifier">allocator_instance3</span><span class="special">);</span>
1131
1132    <span class="comment">//So memory allocated with one can be deallocated with another</span>
1133    <span class="identifier">allocator_instance2</span><span class="special">.</span><span class="identifier">deallocate</span><span class="special">(</span><span class="identifier">allocator_instance</span><span class="special">.</span><span class="identifier">allocate</span><span class="special">(</span><span class="number">1</span><span class="special">),</span> <span class="number">1</span><span class="special">);</span>
1134    <span class="identifier">allocator_instance3</span><span class="special">.</span><span class="identifier">deallocate</span><span class="special">(</span><span class="identifier">allocator_instance2</span><span class="special">.</span><span class="identifier">allocate</span><span class="special">(</span><span class="number">1</span><span class="special">),</span> <span class="number">1</span><span class="special">);</span>
1135
1136    <span class="comment">//The common pool will be destroyed here, since no allocator is</span>
1137    <span class="comment">//attached to the pool</span>
1138    <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span>
1139 <span class="special">}</span>
1140 </pre>
1141 <p>
1142         </p>
1143 </div>
1144 </div>
1145 <div class="section">
1146 <div class="titlepage"><div><div><h3 class="title">
1147 <a name="interprocess.allocators_containers.containers_explained"></a><a class="link" href="allocators_containers.html#interprocess.allocators_containers.containers_explained" title="Interprocess and containers in managed memory segments">Interprocess
1148       and containers in managed memory segments</a>
1149 </h3></div></div></div>
1150 <div class="toc"><dl class="toc">
1151 <dt><span class="section"><a href="allocators_containers.html#interprocess.allocators_containers.containers_explained.stl_container_requirements">Container
1152         requirements for Boost.Interprocess allocators</a></span></dt>
1153 <dt><span class="section"><a href="allocators_containers.html#interprocess.allocators_containers.containers_explained.containers">STL
1154         containers in managed memory segments</a></span></dt>
1155 <dt><span class="section"><a href="allocators_containers.html#interprocess.allocators_containers.containers_explained.where_allocate">Where
1156         is this being allocated?</a></span></dt>
1157 <dt><span class="section"><a href="allocators_containers.html#interprocess.allocators_containers.containers_explained.containers_and_move">Move
1158         semantics in Interprocess containers</a></span></dt>
1159 <dt><span class="section"><a href="allocators_containers.html#interprocess.allocators_containers.containers_explained.containers_of_containers">Containers
1160         of containers</a></span></dt>
1161 </dl></div>
1162 <div class="section">
1163 <div class="titlepage"><div><div><h4 class="title">
1164 <a name="interprocess.allocators_containers.containers_explained.stl_container_requirements"></a><a class="link" href="allocators_containers.html#interprocess.allocators_containers.containers_explained.stl_container_requirements" title="Container requirements for Boost.Interprocess allocators">Container
1165         requirements for Boost.Interprocess allocators</a>
1166 </h4></div></div></div>
1167 <p>
1168           <span class="bold"><strong>Boost.Interprocess</strong></span> STL compatible allocators
1169           offer a STL compatible allocator interface and if they define their internal
1170           <span class="bold"><strong>pointer</strong></span> typedef as a relative pointer,
1171           they can sbe used to place STL containers in shared memory, memory mapped
1172           files or in a user defined memory segment.
1173         </p>
1174 <p>
1175           However, as Scott Meyers mentions in his Effective STL book, Item 10,
1176           <span class="emphasis"><em>"Be aware of allocator conventions and restrictions"</em></span>:
1177         </p>
1178 <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
1179 <li class="listitem">
1180               <span class="emphasis"><em>"the Standard explicitly allows library implementers
1181               to assume that every allocator's pointer typedef is a synonym for T*"</em></span>
1182             </li>
1183 <li class="listitem">
1184               <span class="emphasis"><em>"the Standard says that an implementation of the STL
1185               is permitted to assume that all allocator objects of the same type
1186               are equivalent and always compare equal"</em></span>
1187             </li>
1188 </ul></div>
1189 <p>
1190           Obviously, if any STL implementation ignores pointer typedefs, no smart
1191           pointer can be used as allocator::pointer. If STL implementations assume
1192           all allocator objects of the same type compare equal, it will assume that
1193           two allocators, each one allocating from a different memory pool are equal,
1194           which is a complete disaster.
1195         </p>
1196 <p>
1197           STL containers that we want to place in shared memory or memory mapped
1198           files with <span class="bold"><strong>Boost.Interprocess</strong></span> can't make
1199           any of these assumptions, so:
1200         </p>
1201 <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
1202 <li class="listitem">
1203               STL containers may not assume that memory allocated with an allocator
1204               can be deallocated with other allocators of the same type. All allocators
1205               objects must compare equal only if memory allocated with one object
1206               can be deallocated with the other one, and this can only tested with
1207               operator==() at run-time.
1208             </li>
1209 <li class="listitem">
1210               Containers' internal pointers should be of the type allocator::pointer
1211               and containers may not assume allocator::pointer is a raw pointer.
1212             </li>
1213 <li class="listitem">
1214               All objects must be constructed-destroyed via allocator::construct
1215               and allocator::destroy functions.
1216             </li>
1217 </ul></div>
1218 </div>
1219 <div class="section">
1220 <div class="titlepage"><div><div><h4 class="title">
1221 <a name="interprocess.allocators_containers.containers_explained.containers"></a><a class="link" href="allocators_containers.html#interprocess.allocators_containers.containers_explained.containers" title="STL containers in managed memory segments">STL
1222         containers in managed memory segments</a>
1223 </h4></div></div></div>
1224 <p>
1225           Unfortunately, many STL implementations use raw pointers for internal data
1226           and ignore allocator pointer typedefs and others suppose at some point
1227           that the allocator::typedef is T*. This is because in practice, there wasn't
1228           need of allocators with a pointer typedef different from T* for pooled/node
1229           memory allocators.
1230         </p>
1231 <p>
1232           Until STL implementations handle allocator::pointer typedefs in a generic
1233           way, <span class="bold"><strong>Boost.Interprocess</strong></span> offers the following
1234           classes:
1235         </p>
1236 <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
1237               <span class="bold"><strong>boost:interprocess::vector</strong></span> is the
1238               implementation of <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span></code>
1239               ready to be used in managed memory segments like shared memory. To
1240               use it include:
1241             </li></ul></div>
1242 <pre class="programlisting"><span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">interprocess</span><span class="special">/</span><span class="identifier">containers</span><span class="special">/</span><span class="identifier">vector</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
1243 </pre>
1244 <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
1245               <span class="bold"><strong>boost:interprocess::deque</strong></span> is the implementation
1246               of <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">deque</span></code> ready to be used in managed
1247               memory segments like shared memory. To use it include:
1248             </li></ul></div>
1249 <pre class="programlisting"><span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">interprocess</span><span class="special">/</span><span class="identifier">containers</span><span class="special">/</span><span class="identifier">deque</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
1250 </pre>
1251 <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
1252               <code class="computeroutput">list</code> is the
1253               implementation of <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">list</span></code>
1254               ready to be used in managed memory segments like shared memory. To
1255               use it include:
1256             </li></ul></div>
1257 <pre class="programlisting"><span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">interprocess</span><span class="special">/</span><span class="identifier">containers</span><span class="special">/</span><span class="identifier">list</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
1258 </pre>
1259 <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
1260               <code class="computeroutput">slist</code> is the
1261               implementation of SGI's <code class="computeroutput"><span class="identifier">slist</span></code>
1262               container (singly linked list) ready to be used in managed memory segments
1263               like shared memory. To use it include:
1264             </li></ul></div>
1265 <pre class="programlisting"><span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">interprocess</span><span class="special">/</span><span class="identifier">containers</span><span class="special">/</span><span class="identifier">slist</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
1266 </pre>
1267 <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
1268               <code class="computeroutput">set</code>/ <code class="computeroutput">multiset</code>/ <code class="computeroutput">map</code>/ <code class="computeroutput">multimap</code>
1269               family is the implementation of std::set/multiset/map/multimap family
1270               ready to be used in managed memory segments like shared memory. To
1271               use them include:
1272             </li></ul></div>
1273 <pre class="programlisting"><span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">interprocess</span><span class="special">/</span><span class="identifier">containers</span><span class="special">/</span><span class="identifier">set</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
1274 <span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">interprocess</span><span class="special">/</span><span class="identifier">containers</span><span class="special">/</span><span class="identifier">map</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
1275 </pre>
1276 <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
1277               <code class="computeroutput">flat_set</code>/
1278               <code class="computeroutput">flat_multiset</code>/
1279               <code class="computeroutput">flat_map</code>/
1280               <code class="computeroutput">flat_multimap</code>
1281               classes are the adaptation and extension of Andrei Alexandrescu's famous
1282               AssocVector class from Loki library, ready for the shared memory. These
1283               classes offer the same functionality as <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">set</span><span class="special">/</span><span class="identifier">multiset</span><span class="special">/</span><span class="identifier">map</span><span class="special">/</span><span class="identifier">multimap</span></code>
1284               implemented with an ordered vector, which has faster lookups than the
1285               standard ordered associative containers based on red-black trees, but
1286               slower insertions. To use it include:
1287             </li></ul></div>
1288 <pre class="programlisting"><span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">interprocess</span><span class="special">/</span><span class="identifier">containers</span><span class="special">/</span><span class="identifier">flat_set</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
1289 <span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">interprocess</span><span class="special">/</span><span class="identifier">containers</span><span class="special">/</span><span class="identifier">flat_map</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
1290 </pre>
1291 <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
1292               <code class="computeroutput">basic_string</code>
1293               is the implementation of <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">basic_string</span></code>
1294               ready to be used in managed memory segments like shared memory. It's
1295               implemented using a vector-like contiguous storage, so it has fast
1296               c string conversion and can be used with the <a class="link" href="streams.html#interprocess.streams.vectorstream" title="Formatting directly in your character vector: vectorstream">vectorstream</a>
1297               iostream formatting classes. To use it include:
1298             </li></ul></div>
1299 <pre class="programlisting"><span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">interprocess</span><span class="special">/</span><span class="identifier">containers</span><span class="special">/</span><span class="identifier">string</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
1300 </pre>
1301 <p>
1302           All these containers have the same default arguments as standard containers
1303           and they can be used with other, non <span class="bold"><strong>Boost.Interprocess</strong></span>
1304           allocators (std::allocator, or boost::pool_allocator, for example).
1305         </p>
1306 <p>
1307           To place any of these containers in managed memory segments, we must define
1308           the allocator template parameter with a <span class="bold"><strong>Boost.Interprocess</strong></span>
1309           allocator so that the container allocates the values in the managed memory
1310           segment. To place the container itself in shared memory, we construct it
1311           in the managed memory segment just like any other object with <span class="bold"><strong>Boost.Interprocess</strong></span>:
1312         </p>
1313 <p>
1314 </p>
1315 <pre class="programlisting"><span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">interprocess</span><span class="special">/</span><span class="identifier">containers</span><span class="special">/</span><span class="identifier">vector</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
1316 <span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">interprocess</span><span class="special">/</span><span class="identifier">allocators</span><span class="special">/</span><span class="identifier">allocator</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
1317 <span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">interprocess</span><span class="special">/</span><span class="identifier">managed_shared_memory</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
1318
1319 <span class="keyword">int</span> <span class="identifier">main</span> <span class="special">()</span>
1320 <span class="special">{</span>
1321    <span class="keyword">using</span> <span class="keyword">namespace</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">;</span>
1322    <span class="comment">//Remove shared memory on construction and destruction</span>
1323    <span class="keyword">struct</span> <span class="identifier">shm_remove</span>
1324    <span class="special">{</span>
1325       <span class="identifier">shm_remove</span><span class="special">()</span> <span class="special">{</span> <span class="identifier">shared_memory_object</span><span class="special">::</span><span class="identifier">remove</span><span class="special">(</span><span class="string">"MySharedMemory"</span><span class="special">);</span> <span class="special">}</span>
1326       <span class="special">~</span><span class="identifier">shm_remove</span><span class="special">(){</span> <span class="identifier">shared_memory_object</span><span class="special">::</span><span class="identifier">remove</span><span class="special">(</span><span class="string">"MySharedMemory"</span><span class="special">);</span> <span class="special">}</span>
1327    <span class="special">}</span> <span class="identifier">remover</span><span class="special">;</span>
1328
1329    <span class="comment">//A managed shared memory where we can construct objects</span>
1330    <span class="comment">//associated with a c-string</span>
1331    <span class="identifier">managed_shared_memory</span> <span class="identifier">segment</span><span class="special">(</span><span class="identifier">create_only</span><span class="special">,</span>
1332                                  <span class="string">"MySharedMemory"</span><span class="special">,</span>  <span class="comment">//segment name</span>
1333                                  <span class="number">65536</span><span class="special">);</span>
1334
1335    <span class="comment">//Alias an STL-like allocator of ints that allocates ints from the segment</span>
1336    <span class="keyword">typedef</span> <span class="identifier">allocator</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">,</span> <span class="identifier">managed_shared_memory</span><span class="special">::</span><span class="identifier">segment_manager</span><span class="special">&gt;</span>
1337       <span class="identifier">ShmemAllocator</span><span class="special">;</span>
1338
1339    <span class="comment">//Alias a vector that uses the previous STL-like allocator</span>
1340    <span class="keyword">typedef</span> <span class="identifier">vector</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">,</span> <span class="identifier">ShmemAllocator</span><span class="special">&gt;</span> <span class="identifier">MyVector</span><span class="special">;</span>
1341
1342    <span class="keyword">int</span> <span class="identifier">initVal</span><span class="special">[]</span>        <span class="special">=</span> <span class="special">{</span><span class="number">0</span><span class="special">,</span> <span class="number">1</span><span class="special">,</span> <span class="number">2</span><span class="special">,</span> <span class="number">3</span><span class="special">,</span> <span class="number">4</span><span class="special">,</span> <span class="number">5</span><span class="special">,</span> <span class="number">6</span> <span class="special">};</span>
1343    <span class="keyword">const</span> <span class="keyword">int</span> <span class="special">*</span><span class="identifier">begVal</span>    <span class="special">=</span> <span class="identifier">initVal</span><span class="special">;</span>
1344    <span class="keyword">const</span> <span class="keyword">int</span> <span class="special">*</span><span class="identifier">endVal</span>    <span class="special">=</span> <span class="identifier">initVal</span> <span class="special">+</span> <span class="keyword">sizeof</span><span class="special">(</span><span class="identifier">initVal</span><span class="special">)/</span><span class="keyword">sizeof</span><span class="special">(</span><span class="identifier">initVal</span><span class="special">[</span><span class="number">0</span><span class="special">]);</span>
1345
1346    <span class="comment">//Initialize the STL-like allocator</span>
1347    <span class="keyword">const</span> <span class="identifier">ShmemAllocator</span> <span class="identifier">alloc_inst</span> <span class="special">(</span><span class="identifier">segment</span><span class="special">.</span><span class="identifier">get_segment_manager</span><span class="special">());</span>
1348
1349    <span class="comment">//Construct the vector in the shared memory segment with the STL-like allocator</span>
1350    <span class="comment">//from a range of iterators</span>
1351    <span class="identifier">MyVector</span> <span class="special">*</span><span class="identifier">myvector</span> <span class="special">=</span>
1352       <span class="identifier">segment</span><span class="special">.</span><span class="identifier">construct</span><span class="special">&lt;</span><span class="identifier">MyVector</span><span class="special">&gt;</span>
1353          <span class="special">(</span><span class="string">"MyVector"</span><span class="special">)/*</span><span class="identifier">object</span> <span class="identifier">name</span><span class="special">*/</span>
1354          <span class="special">(</span><span class="identifier">begVal</span>     <span class="comment">/*first ctor parameter*/</span><span class="special">,</span>
1355          <span class="identifier">endVal</span>     <span class="comment">/*second ctor parameter*/</span><span class="special">,</span>
1356          <span class="identifier">alloc_inst</span> <span class="comment">/*third ctor parameter*/</span><span class="special">);</span>
1357
1358    <span class="comment">//Use vector as your want</span>
1359    <span class="identifier">std</span><span class="special">::</span><span class="identifier">sort</span><span class="special">(</span><span class="identifier">myvector</span><span class="special">-&gt;</span><span class="identifier">rbegin</span><span class="special">(),</span> <span class="identifier">myvector</span><span class="special">-&gt;</span><span class="identifier">rend</span><span class="special">());</span>
1360    <span class="comment">// . . .</span>
1361    <span class="comment">//When done, destroy and delete vector from the segment</span>
1362    <span class="identifier">segment</span><span class="special">.</span><span class="identifier">destroy</span><span class="special">&lt;</span><span class="identifier">MyVector</span><span class="special">&gt;(</span><span class="string">"MyVector"</span><span class="special">);</span>
1363    <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span>
1364 <span class="special">}</span>
1365 </pre>
1366 <p>
1367         </p>
1368 <p>
1369           These containers also show how easy is to create/modify an existing container
1370           making possible to place it in shared memory.
1371         </p>
1372 </div>
1373 <div class="section">
1374 <div class="titlepage"><div><div><h4 class="title">
1375 <a name="interprocess.allocators_containers.containers_explained.where_allocate"></a><a class="link" href="allocators_containers.html#interprocess.allocators_containers.containers_explained.where_allocate" title="Where is this being allocated?">Where
1376         is this being allocated?</a>
1377 </h4></div></div></div>
1378 <p>
1379           <span class="bold"><strong>Boost.Interprocess</strong></span> containers are placed
1380           in shared memory/memory mapped files, etc... using two mechanisms <span class="bold"><strong>at the same time</strong></span>:
1381         </p>
1382 <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
1383 <li class="listitem">
1384               <span class="bold"><strong>Boost.Interprocess </strong></span><code class="computeroutput"><span class="identifier">construct</span><span class="special">&lt;&gt;</span></code>, <code class="computeroutput"><span class="identifier">find_or_construct</span><span class="special">&lt;&gt;</span></code>... functions. These functions
1385               place a C++ object in the shared memory/memory mapped file. But this
1386               places only the object, but <span class="bold"><strong>not</strong></span> the
1387               memory that this object may allocate dynamically.
1388             </li>
1389 <li class="listitem">
1390               Shared memory allocators. These allow allocating shared memory/memory
1391               mapped file portions so that containers can allocate dynamically fragments
1392               of memory to store newly inserted elements.
1393             </li>
1394 </ul></div>
1395 <p>
1396           This means that to place any <span class="bold"><strong>Boost.Interprocess</strong></span>
1397           container (including <span class="bold"><strong>Boost.Interprocess</strong></span>
1398           strings) in shared memory or memory mapped files, containers <span class="bold"><strong>must</strong></span>:
1399         </p>
1400 <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
1401 <li class="listitem">
1402               Define their template allocator parameter to a <span class="bold"><strong>Boost.Interprocess</strong></span>
1403               allocator.
1404             </li>
1405 <li class="listitem">
1406               Every container constructor must take the <span class="bold"><strong>Boost.Interprocess</strong></span>
1407               allocator as parameter.
1408             </li>
1409 <li class="listitem">
1410               You must use construct&lt;&gt;/find_or_construct&lt;&gt;... functions
1411               to place the container in the managed memory.
1412             </li>
1413 </ul></div>
1414 <p>
1415           If you do the first two points but you don't use <code class="computeroutput"><span class="identifier">construct</span><span class="special">&lt;&gt;</span></code> or <code class="computeroutput"><span class="identifier">find_or_construct</span><span class="special">&lt;&gt;</span></code> you are creating a container placed
1416           <span class="bold"><strong>only</strong></span> in your process but that allocates
1417           memory for contained types from shared memory/memory mapped file.
1418         </p>
1419 <p>
1420           Let's see an example:
1421         </p>
1422 <p>
1423 </p>
1424 <pre class="programlisting"><span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">interprocess</span><span class="special">/</span><span class="identifier">managed_shared_memory</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
1425 <span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">interprocess</span><span class="special">/</span><span class="identifier">containers</span><span class="special">/</span><span class="identifier">vector</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
1426 <span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">interprocess</span><span class="special">/</span><span class="identifier">containers</span><span class="special">/</span><span class="identifier">string</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
1427 <span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">interprocess</span><span class="special">/</span><span class="identifier">allocators</span><span class="special">/</span><span class="identifier">allocator</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
1428
1429 <span class="keyword">int</span> <span class="identifier">main</span> <span class="special">()</span>
1430 <span class="special">{</span>
1431    <span class="keyword">using</span> <span class="keyword">namespace</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">;</span>
1432    <span class="comment">//Typedefs</span>
1433    <span class="keyword">typedef</span> <span class="identifier">allocator</span><span class="special">&lt;</span><span class="keyword">char</span><span class="special">,</span> <span class="identifier">managed_shared_memory</span><span class="special">::</span><span class="identifier">segment_manager</span><span class="special">&gt;</span>
1434       <span class="identifier">CharAllocator</span><span class="special">;</span>
1435    <span class="keyword">typedef</span> <span class="identifier">basic_string</span><span class="special">&lt;</span><span class="keyword">char</span><span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">char_traits</span><span class="special">&lt;</span><span class="keyword">char</span><span class="special">&gt;,</span> <span class="identifier">CharAllocator</span><span class="special">&gt;</span>
1436       <span class="identifier">MyShmString</span><span class="special">;</span>
1437    <span class="keyword">typedef</span> <span class="identifier">allocator</span><span class="special">&lt;</span><span class="identifier">MyShmString</span><span class="special">,</span> <span class="identifier">managed_shared_memory</span><span class="special">::</span><span class="identifier">segment_manager</span><span class="special">&gt;</span>
1438       <span class="identifier">StringAllocator</span><span class="special">;</span>
1439    <span class="keyword">typedef</span> <span class="identifier">vector</span><span class="special">&lt;</span><span class="identifier">MyShmString</span><span class="special">,</span> <span class="identifier">StringAllocator</span><span class="special">&gt;</span>
1440       <span class="identifier">MyShmStringVector</span><span class="special">;</span>
1441
1442    <span class="comment">//Open shared memory</span>
1443    <span class="comment">//Remove shared memory on construction and destruction</span>
1444    <span class="keyword">struct</span> <span class="identifier">shm_remove</span>
1445    <span class="special">{</span>
1446       <span class="identifier">shm_remove</span><span class="special">()</span> <span class="special">{</span> <span class="identifier">shared_memory_object</span><span class="special">::</span><span class="identifier">remove</span><span class="special">(</span><span class="string">"MySharedMemory"</span><span class="special">);</span> <span class="special">}</span>
1447       <span class="special">~</span><span class="identifier">shm_remove</span><span class="special">(){</span> <span class="identifier">shared_memory_object</span><span class="special">::</span><span class="identifier">remove</span><span class="special">(</span><span class="string">"MySharedMemory"</span><span class="special">);</span> <span class="special">}</span>
1448    <span class="special">}</span> <span class="identifier">remover</span><span class="special">;</span>
1449
1450    <span class="identifier">managed_shared_memory</span> <span class="identifier">shm</span><span class="special">(</span><span class="identifier">create_only</span><span class="special">,</span> <span class="string">"MySharedMemory"</span><span class="special">,</span> <span class="number">10000</span><span class="special">);</span>
1451
1452    <span class="comment">//Create allocators</span>
1453    <span class="identifier">CharAllocator</span>     <span class="identifier">charallocator</span>  <span class="special">(</span><span class="identifier">shm</span><span class="special">.</span><span class="identifier">get_segment_manager</span><span class="special">());</span>
1454    <span class="identifier">StringAllocator</span>   <span class="identifier">stringallocator</span><span class="special">(</span><span class="identifier">shm</span><span class="special">.</span><span class="identifier">get_segment_manager</span><span class="special">());</span>
1455
1456    <span class="comment">//This string is in only in this process (the pointer pointing to the</span>
1457    <span class="comment">//buffer that will hold the text is not in shared memory).</span>
1458    <span class="comment">//But the buffer that will hold "this is my text" is allocated from</span>
1459    <span class="comment">//shared memory</span>
1460    <span class="identifier">MyShmString</span> <span class="identifier">mystring</span><span class="special">(</span><span class="identifier">charallocator</span><span class="special">);</span>
1461    <span class="identifier">mystring</span> <span class="special">=</span> <span class="string">"this is my text"</span><span class="special">;</span>
1462
1463    <span class="comment">//This vector is only in this process (the pointer pointing to the</span>
1464    <span class="comment">//buffer that will hold the MyShmString-s is not in shared memory).</span>
1465    <span class="comment">//But the buffer that will hold 10 MyShmString-s is allocated from</span>
1466    <span class="comment">//shared memory using StringAllocator. Since strings use a shared</span>
1467    <span class="comment">//memory allocator (CharAllocator) the 10 buffers that hold</span>
1468    <span class="comment">//"this is my text" text are also in shared memory.</span>
1469    <span class="identifier">MyShmStringVector</span> <span class="identifier">myvector</span><span class="special">(</span><span class="identifier">stringallocator</span><span class="special">);</span>
1470    <span class="identifier">myvector</span><span class="special">.</span><span class="identifier">insert</span><span class="special">(</span><span class="identifier">myvector</span><span class="special">.</span><span class="identifier">begin</span><span class="special">(),</span> <span class="number">10</span><span class="special">,</span> <span class="identifier">mystring</span><span class="special">);</span>
1471
1472    <span class="comment">//This vector is fully constructed in shared memory. All pointers</span>
1473    <span class="comment">//buffers are constructed in the same shared memory segment</span>
1474    <span class="comment">//This vector can be safely accessed from other processes.</span>
1475    <span class="identifier">MyShmStringVector</span> <span class="special">*</span><span class="identifier">myshmvector</span> <span class="special">=</span>
1476       <span class="identifier">shm</span><span class="special">.</span><span class="identifier">construct</span><span class="special">&lt;</span><span class="identifier">MyShmStringVector</span><span class="special">&gt;(</span><span class="string">"myshmvector"</span><span class="special">)(</span><span class="identifier">stringallocator</span><span class="special">);</span>
1477    <span class="identifier">myshmvector</span><span class="special">-&gt;</span><span class="identifier">insert</span><span class="special">(</span><span class="identifier">myshmvector</span><span class="special">-&gt;</span><span class="identifier">begin</span><span class="special">(),</span> <span class="number">10</span><span class="special">,</span> <span class="identifier">mystring</span><span class="special">);</span>
1478
1479    <span class="comment">//Destroy vector. This will free all strings that the vector contains</span>
1480    <span class="identifier">shm</span><span class="special">.</span><span class="identifier">destroy_ptr</span><span class="special">(</span><span class="identifier">myshmvector</span><span class="special">);</span>
1481    <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span>
1482 <span class="special">}</span>
1483 </pre>
1484 <p>
1485         </p>
1486 </div>
1487 <div class="section">
1488 <div class="titlepage"><div><div><h4 class="title">
1489 <a name="interprocess.allocators_containers.containers_explained.containers_and_move"></a><a class="link" href="allocators_containers.html#interprocess.allocators_containers.containers_explained.containers_and_move" title="Move semantics in Interprocess containers">Move
1490         semantics in Interprocess containers</a>
1491 </h4></div></div></div>
1492 <p>
1493           <span class="bold"><strong>Boost.Interprocess</strong></span> containers support
1494           move semantics, which means that the contents of a container can be moved
1495           from a container two another one, without any copying. The contents of
1496           the source container are transferred to the target container and the source
1497           container is left in default-constructed state.
1498         </p>
1499 <p>
1500           When using containers of containers, we can also use move-semantics to
1501           insert objects in the container, avoiding unnecessary copies.
1502         </p>
1503 <p>
1504           To transfer the contents of a container to another one, use <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">move</span><span class="special">()</span></code>
1505           function, as shown in the example. For more details about functions supporting
1506           move-semantics, see the reference section of Boost.Interprocess containers:
1507         </p>
1508 <p>
1509 </p>
1510 <pre class="programlisting"><span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">interprocess</span><span class="special">/</span><span class="identifier">managed_shared_memory</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
1511 <span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">interprocess</span><span class="special">/</span><span class="identifier">containers</span><span class="special">/</span><span class="identifier">vector</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
1512 <span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">interprocess</span><span class="special">/</span><span class="identifier">containers</span><span class="special">/</span><span class="identifier">string</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
1513 <span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">interprocess</span><span class="special">/</span><span class="identifier">allocators</span><span class="special">/</span><span class="identifier">allocator</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
1514 <span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">cassert</span><span class="special">&gt;</span>
1515
1516 <span class="keyword">int</span> <span class="identifier">main</span> <span class="special">()</span>
1517 <span class="special">{</span>
1518    <span class="keyword">using</span> <span class="keyword">namespace</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">;</span>
1519
1520    <span class="comment">//Typedefs</span>
1521    <span class="keyword">typedef</span> <span class="identifier">managed_shared_memory</span><span class="special">::</span><span class="identifier">segment_manager</span>     <span class="identifier">SegmentManager</span><span class="special">;</span>
1522    <span class="keyword">typedef</span> <span class="identifier">allocator</span><span class="special">&lt;</span><span class="keyword">char</span><span class="special">,</span> <span class="identifier">SegmentManager</span><span class="special">&gt;</span>            <span class="identifier">CharAllocator</span><span class="special">;</span>
1523    <span class="keyword">typedef</span> <span class="identifier">basic_string</span><span class="special">&lt;</span><span class="keyword">char</span><span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">char_traits</span><span class="special">&lt;</span><span class="keyword">char</span><span class="special">&gt;</span>
1524                         <span class="special">,</span><span class="identifier">CharAllocator</span><span class="special">&gt;</span>                <span class="identifier">MyShmString</span><span class="special">;</span>
1525    <span class="keyword">typedef</span> <span class="identifier">allocator</span><span class="special">&lt;</span><span class="identifier">MyShmString</span><span class="special">,</span> <span class="identifier">SegmentManager</span><span class="special">&gt;</span>     <span class="identifier">StringAllocator</span><span class="special">;</span>
1526    <span class="keyword">typedef</span> <span class="identifier">vector</span><span class="special">&lt;</span><span class="identifier">MyShmString</span><span class="special">,</span> <span class="identifier">StringAllocator</span><span class="special">&gt;</span>       <span class="identifier">MyShmStringVector</span><span class="special">;</span>
1527
1528    <span class="comment">//Remove shared memory on construction and destruction</span>
1529    <span class="keyword">struct</span> <span class="identifier">shm_remove</span>
1530    <span class="special">{</span>
1531       <span class="identifier">shm_remove</span><span class="special">()</span> <span class="special">{</span> <span class="identifier">shared_memory_object</span><span class="special">::</span><span class="identifier">remove</span><span class="special">(</span><span class="string">"MySharedMemory"</span><span class="special">);</span> <span class="special">}</span>
1532       <span class="special">~</span><span class="identifier">shm_remove</span><span class="special">(){</span> <span class="identifier">shared_memory_object</span><span class="special">::</span><span class="identifier">remove</span><span class="special">(</span><span class="string">"MySharedMemory"</span><span class="special">);</span> <span class="special">}</span>
1533    <span class="special">}</span> <span class="identifier">remover</span><span class="special">;</span>
1534
1535    <span class="identifier">managed_shared_memory</span> <span class="identifier">shm</span><span class="special">(</span><span class="identifier">create_only</span><span class="special">,</span> <span class="string">"MySharedMemory"</span><span class="special">,</span> <span class="number">10000</span><span class="special">);</span>
1536
1537    <span class="comment">//Create allocators</span>
1538    <span class="identifier">CharAllocator</span>     <span class="identifier">charallocator</span>  <span class="special">(</span><span class="identifier">shm</span><span class="special">.</span><span class="identifier">get_segment_manager</span><span class="special">());</span>
1539    <span class="identifier">StringAllocator</span>   <span class="identifier">stringallocator</span><span class="special">(</span><span class="identifier">shm</span><span class="special">.</span><span class="identifier">get_segment_manager</span><span class="special">());</span>
1540
1541    <span class="comment">//Create a vector of strings in shared memory.</span>
1542    <span class="identifier">MyShmStringVector</span> <span class="special">*</span><span class="identifier">myshmvector</span> <span class="special">=</span>
1543       <span class="identifier">shm</span><span class="special">.</span><span class="identifier">construct</span><span class="special">&lt;</span><span class="identifier">MyShmStringVector</span><span class="special">&gt;(</span><span class="string">"myshmvector"</span><span class="special">)(</span><span class="identifier">stringallocator</span><span class="special">);</span>
1544
1545    <span class="comment">//Insert 50 strings in shared memory. The strings will be allocated</span>
1546    <span class="comment">//only once and no string copy-constructor will be called when inserting</span>
1547    <span class="comment">//strings, leading to a great performance.</span>
1548    <span class="identifier">MyShmString</span> <span class="identifier">string_to_compare</span><span class="special">(</span><span class="identifier">charallocator</span><span class="special">);</span>
1549    <span class="identifier">string_to_compare</span> <span class="special">=</span> <span class="string">"this is a long, long, long, long, long, long, string..."</span><span class="special">;</span>
1550
1551    <span class="identifier">myshmvector</span><span class="special">-&gt;</span><span class="identifier">reserve</span><span class="special">(</span><span class="number">50</span><span class="special">);</span>
1552    <span class="keyword">for</span><span class="special">(</span><span class="keyword">int</span> <span class="identifier">i</span> <span class="special">=</span> <span class="number">0</span><span class="special">;</span> <span class="identifier">i</span> <span class="special">&lt;</span> <span class="number">50</span><span class="special">;</span> <span class="special">++</span><span class="identifier">i</span><span class="special">){</span>
1553       <span class="identifier">MyShmString</span> <span class="identifier">move_me</span><span class="special">(</span><span class="identifier">string_to_compare</span><span class="special">);</span>
1554       <span class="comment">//In the following line, no string copy-constructor will be called.</span>
1555       <span class="comment">//"move_me"'s contents will be transferred to the string created in</span>
1556       <span class="comment">//the vector</span>
1557       <span class="identifier">myshmvector</span><span class="special">-&gt;</span><span class="identifier">push_back</span><span class="special">(</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">move_me</span><span class="special">));</span>
1558
1559       <span class="comment">//The source string is in default constructed state</span>
1560       <span class="identifier">assert</span><span class="special">(</span><span class="identifier">move_me</span><span class="special">.</span><span class="identifier">empty</span><span class="special">());</span>
1561
1562       <span class="comment">//The newly created string will be equal to the "move_me"'s old contents</span>
1563       <span class="identifier">assert</span><span class="special">(</span><span class="identifier">myshmvector</span><span class="special">-&gt;</span><span class="identifier">back</span><span class="special">()</span> <span class="special">==</span> <span class="identifier">string_to_compare</span><span class="special">);</span>
1564    <span class="special">}</span>
1565
1566    <span class="comment">//Now erase a string...</span>
1567    <span class="identifier">myshmvector</span><span class="special">-&gt;</span><span class="identifier">pop_back</span><span class="special">();</span>
1568
1569    <span class="comment">//...And insert one in the first position.</span>
1570    <span class="comment">//No string copy-constructor or assignments will be called, but</span>
1571    <span class="comment">//move constructors and move-assignments. No memory allocation</span>
1572    <span class="comment">//function will be called in this operations!!</span>
1573    <span class="identifier">myshmvector</span><span class="special">-&gt;</span><span class="identifier">insert</span><span class="special">(</span><span class="identifier">myshmvector</span><span class="special">-&gt;</span><span class="identifier">begin</span><span class="special">(),</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">string_to_compare</span><span class="special">));</span>
1574
1575    <span class="comment">//Destroy vector. This will free all strings that the vector contains</span>
1576    <span class="identifier">shm</span><span class="special">.</span><span class="identifier">destroy_ptr</span><span class="special">(</span><span class="identifier">myshmvector</span><span class="special">);</span>
1577    <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span>
1578 <span class="special">}</span>
1579 </pre>
1580 <p>
1581         </p>
1582 </div>
1583 <div class="section">
1584 <div class="titlepage"><div><div><h4 class="title">
1585 <a name="interprocess.allocators_containers.containers_explained.containers_of_containers"></a><a class="link" href="allocators_containers.html#interprocess.allocators_containers.containers_explained.containers_of_containers" title="Containers of containers">Containers
1586         of containers</a>
1587 </h4></div></div></div>
1588 <p>
1589           When creating containers of containers, each container needs an allocator.
1590           To avoid using several allocators with complex type definitions, we can
1591           take advantage of the type erasure provided by void allocators and the
1592           ability to implicitly convert void allocators in allocators that allocate
1593           other types.
1594         </p>
1595 <p>
1596           Here we have an example that builds a map in shared memory. Key is a string
1597           and the mapped type is a class that stores several containers:
1598         </p>
1599 <p>
1600 </p>
1601 <pre class="programlisting"><span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">interprocess</span><span class="special">/</span><span class="identifier">managed_shared_memory</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
1602 <span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">interprocess</span><span class="special">/</span><span class="identifier">allocators</span><span class="special">/</span><span class="identifier">allocator</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
1603 <span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">interprocess</span><span class="special">/</span><span class="identifier">containers</span><span class="special">/</span><span class="identifier">map</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
1604 <span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">interprocess</span><span class="special">/</span><span class="identifier">containers</span><span class="special">/</span><span class="identifier">vector</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
1605 <span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">interprocess</span><span class="special">/</span><span class="identifier">containers</span><span class="special">/</span><span class="identifier">string</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
1606
1607 <span class="keyword">using</span> <span class="keyword">namespace</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">;</span>
1608
1609 <span class="comment">//Typedefs of allocators and containers</span>
1610 <span class="keyword">typedef</span> <span class="identifier">managed_shared_memory</span><span class="special">::</span><span class="identifier">segment_manager</span>                       <span class="identifier">segment_manager_t</span><span class="special">;</span>
1611 <span class="keyword">typedef</span> <span class="identifier">allocator</span><span class="special">&lt;</span><span class="keyword">void</span><span class="special">,</span> <span class="identifier">segment_manager_t</span><span class="special">&gt;</span>                           <span class="identifier">void_allocator</span><span class="special">;</span>
1612 <span class="keyword">typedef</span> <span class="identifier">allocator</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">,</span> <span class="identifier">segment_manager_t</span><span class="special">&gt;</span>                            <span class="identifier">int_allocator</span><span class="special">;</span>
1613 <span class="keyword">typedef</span> <span class="identifier">vector</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">,</span> <span class="identifier">int_allocator</span><span class="special">&gt;</span>                                   <span class="identifier">int_vector</span><span class="special">;</span>
1614 <span class="keyword">typedef</span> <span class="identifier">allocator</span><span class="special">&lt;</span><span class="identifier">int_vector</span><span class="special">,</span> <span class="identifier">segment_manager_t</span><span class="special">&gt;</span>                     <span class="identifier">int_vector_allocator</span><span class="special">;</span>
1615 <span class="keyword">typedef</span> <span class="identifier">vector</span><span class="special">&lt;</span><span class="identifier">int_vector</span><span class="special">,</span> <span class="identifier">int_vector_allocator</span><span class="special">&gt;</span>                     <span class="identifier">int_vector_vector</span><span class="special">;</span>
1616 <span class="keyword">typedef</span> <span class="identifier">allocator</span><span class="special">&lt;</span><span class="keyword">char</span><span class="special">,</span> <span class="identifier">segment_manager_t</span><span class="special">&gt;</span>                           <span class="identifier">char_allocator</span><span class="special">;</span>
1617 <span class="keyword">typedef</span> <span class="identifier">basic_string</span><span class="special">&lt;</span><span class="keyword">char</span><span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">char_traits</span><span class="special">&lt;</span><span class="keyword">char</span><span class="special">&gt;,</span> <span class="identifier">char_allocator</span><span class="special">&gt;</span>   <span class="identifier">char_string</span><span class="special">;</span>
1618
1619 <span class="keyword">class</span> <span class="identifier">complex_data</span>
1620 <span class="special">{</span>
1621    <span class="keyword">int</span>               <span class="identifier">id_</span><span class="special">;</span>
1622    <span class="identifier">char_string</span>       <span class="identifier">char_string_</span><span class="special">;</span>
1623    <span class="identifier">int_vector_vector</span> <span class="identifier">int_vector_vector_</span><span class="special">;</span>
1624
1625    <span class="keyword">public</span><span class="special">:</span>
1626    <span class="comment">//Since void_allocator is convertible to any other allocator&lt;T&gt;, we can simplify</span>
1627    <span class="comment">//the initialization taking just one allocator for all inner containers.</span>
1628    <span class="identifier">complex_data</span><span class="special">(</span><span class="keyword">int</span> <span class="identifier">id</span><span class="special">,</span> <span class="keyword">const</span> <span class="keyword">char</span> <span class="special">*</span><span class="identifier">name</span><span class="special">,</span> <span class="keyword">const</span> <span class="identifier">void_allocator</span> <span class="special">&amp;</span><span class="identifier">void_alloc</span><span class="special">)</span>
1629       <span class="special">:</span> <span class="identifier">id_</span><span class="special">(</span><span class="identifier">id</span><span class="special">),</span> <span class="identifier">char_string_</span><span class="special">(</span><span class="identifier">name</span><span class="special">,</span> <span class="identifier">void_alloc</span><span class="special">),</span> <span class="identifier">int_vector_vector_</span><span class="special">(</span><span class="identifier">void_alloc</span><span class="special">)</span>
1630    <span class="special">{}</span>
1631    <span class="comment">//Other members...</span>
1632 <span class="special">};</span>
1633
1634 <span class="comment">//Definition of the map holding a string as key and complex_data as mapped type</span>
1635 <span class="keyword">typedef</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">pair</span><span class="special">&lt;</span><span class="keyword">const</span> <span class="identifier">char_string</span><span class="special">,</span> <span class="identifier">complex_data</span><span class="special">&gt;</span>                      <span class="identifier">map_value_type</span><span class="special">;</span>
1636 <span class="keyword">typedef</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">pair</span><span class="special">&lt;</span><span class="identifier">char_string</span><span class="special">,</span> <span class="identifier">complex_data</span><span class="special">&gt;</span>                            <span class="identifier">movable_to_map_value_type</span><span class="special">;</span>
1637 <span class="keyword">typedef</span> <span class="identifier">allocator</span><span class="special">&lt;</span><span class="identifier">map_value_type</span><span class="special">,</span> <span class="identifier">segment_manager_t</span><span class="special">&gt;</span>                    <span class="identifier">map_value_type_allocator</span><span class="special">;</span>
1638 <span class="keyword">typedef</span> <span class="identifier">map</span><span class="special">&lt;</span> <span class="identifier">char_string</span><span class="special">,</span> <span class="identifier">complex_data</span>
1639            <span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">less</span><span class="special">&lt;</span><span class="identifier">char_string</span><span class="special">&gt;,</span> <span class="identifier">map_value_type_allocator</span><span class="special">&gt;</span>          <span class="identifier">complex_map_type</span><span class="special">;</span>
1640
1641 <span class="keyword">int</span> <span class="identifier">main</span> <span class="special">()</span>
1642 <span class="special">{</span>
1643    <span class="comment">//Remove shared memory on construction and destruction</span>
1644    <span class="keyword">struct</span> <span class="identifier">shm_remove</span>
1645    <span class="special">{</span>
1646       <span class="identifier">shm_remove</span><span class="special">()</span> <span class="special">{</span> <span class="identifier">shared_memory_object</span><span class="special">::</span><span class="identifier">remove</span><span class="special">(</span><span class="string">"MySharedMemory"</span><span class="special">);</span> <span class="special">}</span>
1647       <span class="special">~</span><span class="identifier">shm_remove</span><span class="special">(){</span> <span class="identifier">shared_memory_object</span><span class="special">::</span><span class="identifier">remove</span><span class="special">(</span><span class="string">"MySharedMemory"</span><span class="special">);</span> <span class="special">}</span>
1648    <span class="special">}</span> <span class="identifier">remover</span><span class="special">;</span>
1649
1650    <span class="comment">//Create shared memory</span>
1651    <span class="identifier">managed_shared_memory</span> <span class="identifier">segment</span><span class="special">(</span><span class="identifier">create_only</span><span class="special">,</span><span class="string">"MySharedMemory"</span><span class="special">,</span> <span class="number">65536</span><span class="special">);</span>
1652
1653    <span class="comment">//An allocator convertible to any allocator&lt;T, segment_manager_t&gt; type</span>
1654    <span class="identifier">void_allocator</span> <span class="identifier">alloc_inst</span> <span class="special">(</span><span class="identifier">segment</span><span class="special">.</span><span class="identifier">get_segment_manager</span><span class="special">());</span>
1655
1656    <span class="comment">//Construct the shared memory map and fill it</span>
1657    <span class="identifier">complex_map_type</span> <span class="special">*</span><span class="identifier">mymap</span> <span class="special">=</span> <span class="identifier">segment</span><span class="special">.</span><span class="identifier">construct</span><span class="special">&lt;</span><span class="identifier">complex_map_type</span><span class="special">&gt;</span>
1658       <span class="comment">//(object name), (first ctor parameter, second ctor parameter)</span>
1659          <span class="special">(</span><span class="string">"MyMap"</span><span class="special">)(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">less</span><span class="special">&lt;</span><span class="identifier">char_string</span><span class="special">&gt;(),</span> <span class="identifier">alloc_inst</span><span class="special">);</span>
1660
1661    <span class="keyword">for</span><span class="special">(</span><span class="keyword">int</span> <span class="identifier">i</span> <span class="special">=</span> <span class="number">0</span><span class="special">;</span> <span class="identifier">i</span> <span class="special">&lt;</span> <span class="number">100</span><span class="special">;</span> <span class="special">++</span><span class="identifier">i</span><span class="special">){</span>
1662       <span class="comment">//Both key(string) and value(complex_data) need an allocator in their constructors</span>
1663       <span class="identifier">char_string</span>  <span class="identifier">key_object</span><span class="special">(</span><span class="identifier">alloc_inst</span><span class="special">);</span>
1664       <span class="identifier">complex_data</span> <span class="identifier">mapped_object</span><span class="special">(</span><span class="identifier">i</span><span class="special">,</span> <span class="string">"default_name"</span><span class="special">,</span> <span class="identifier">alloc_inst</span><span class="special">);</span>
1665       <span class="identifier">map_value_type</span> <span class="identifier">value</span><span class="special">(</span><span class="identifier">key_object</span><span class="special">,</span> <span class="identifier">mapped_object</span><span class="special">);</span>
1666       <span class="comment">//Modify values and insert them in the map</span>
1667       <span class="identifier">mymap</span><span class="special">-&gt;</span><span class="identifier">insert</span><span class="special">(</span><span class="identifier">value</span><span class="special">);</span>
1668    <span class="special">}</span>
1669    <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span>
1670 <span class="special">}</span>
1671 </pre>
1672 <p>
1673         </p>
1674 </div>
1675 </div>
1676 <div class="section">
1677 <div class="titlepage"><div><div><h3 class="title">
1678 <a name="interprocess.allocators_containers.additional_containers"></a><a class="link" href="allocators_containers.html#interprocess.allocators_containers.additional_containers" title="Boost containers compatible with Boost.Interprocess">Boost
1679       containers compatible with Boost.Interprocess</a>
1680 </h3></div></div></div>
1681 <div class="toc"><dl class="toc">
1682 <dt><span class="section"><a href="allocators_containers.html#interprocess.allocators_containers.additional_containers.unordered">Boost
1683         unordered containers</a></span></dt>
1684 <dt><span class="section"><a href="allocators_containers.html#interprocess.allocators_containers.additional_containers.multi_index">Boost.MultiIndex
1685         containers</a></span></dt>
1686 </dl></div>
1687 <p>
1688         As mentioned, container developers might need to change their implementation
1689         to make them compatible with Boost.Interprocess, because implementation usually
1690         ignore allocators with smart pointers. Hopefully several Boost containers
1691         are compatible with <span class="bold"><strong>Interprocess</strong></span>.
1692       </p>
1693 <div class="section">
1694 <div class="titlepage"><div><div><h4 class="title">
1695 <a name="interprocess.allocators_containers.additional_containers.unordered"></a><a class="link" href="allocators_containers.html#interprocess.allocators_containers.additional_containers.unordered" title="Boost unordered containers">Boost
1696         unordered containers</a>
1697 </h4></div></div></div>
1698 <p>
1699           <span class="bold"><strong>Boost.Unordered</strong></span> containers are compatible
1700           with Interprocess, so programmers can store hash containers in shared memory
1701           and memory mapped files. Here is a small example storing <code class="computeroutput"><span class="identifier">unordered_map</span></code> in shared memory:
1702         </p>
1703 <p>
1704 </p>
1705 <pre class="programlisting"><span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">interprocess</span><span class="special">/</span><span class="identifier">managed_shared_memory</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
1706 <span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">interprocess</span><span class="special">/</span><span class="identifier">allocators</span><span class="special">/</span><span class="identifier">allocator</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
1707
1708
1709 <span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">unordered_map</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>     <span class="comment">//boost::unordered_map</span>
1710
1711
1712 <span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">functional</span><span class="special">&gt;</span>                  <span class="comment">//std::equal_to</span>
1713 <span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">functional</span><span class="special">/</span><span class="identifier">hash</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>   <span class="comment">//boost::hash</span>
1714
1715
1716 <span class="keyword">int</span> <span class="identifier">main</span> <span class="special">()</span>
1717 <span class="special">{</span>
1718    <span class="keyword">using</span> <span class="keyword">namespace</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">;</span>
1719    <span class="comment">//Remove shared memory on construction and destruction</span>
1720    <span class="keyword">struct</span> <span class="identifier">shm_remove</span>
1721    <span class="special">{</span>
1722       <span class="identifier">shm_remove</span><span class="special">()</span> <span class="special">{</span> <span class="identifier">shared_memory_object</span><span class="special">::</span><span class="identifier">remove</span><span class="special">(</span><span class="string">"MySharedMemory"</span><span class="special">);</span> <span class="special">}</span>
1723       <span class="special">~</span><span class="identifier">shm_remove</span><span class="special">(){</span> <span class="identifier">shared_memory_object</span><span class="special">::</span><span class="identifier">remove</span><span class="special">(</span><span class="string">"MySharedMemory"</span><span class="special">);</span> <span class="special">}</span>
1724    <span class="special">}</span> <span class="identifier">remover</span><span class="special">;</span>
1725
1726    <span class="comment">//Create shared memory</span>
1727    <span class="identifier">managed_shared_memory</span> <span class="identifier">segment</span><span class="special">(</span><span class="identifier">create_only</span><span class="special">,</span> <span class="string">"MySharedMemory"</span><span class="special">,</span> <span class="number">65536</span><span class="special">);</span>
1728
1729    <span class="comment">//Note that unordered_map&lt;Key, MappedType&gt;'s value_type is std::pair&lt;const Key, MappedType&gt;,</span>
1730    <span class="comment">//so the allocator must allocate that pair.</span>
1731    <span class="keyword">typedef</span> <span class="keyword">int</span>    <span class="identifier">KeyType</span><span class="special">;</span>
1732    <span class="keyword">typedef</span> <span class="keyword">float</span>  <span class="identifier">MappedType</span><span class="special">;</span>
1733    <span class="keyword">typedef</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">pair</span><span class="special">&lt;</span><span class="keyword">const</span> <span class="keyword">int</span><span class="special">,</span> <span class="keyword">float</span><span class="special">&gt;</span> <span class="identifier">ValueType</span><span class="special">;</span>
1734
1735    <span class="comment">//Typedef the allocator</span>
1736    <span class="keyword">typedef</span> <span class="identifier">allocator</span><span class="special">&lt;</span><span class="identifier">ValueType</span><span class="special">,</span> <span class="identifier">managed_shared_memory</span><span class="special">::</span><span class="identifier">segment_manager</span><span class="special">&gt;</span> <span class="identifier">ShmemAllocator</span><span class="special">;</span>
1737
1738    <span class="comment">//Alias an unordered_map of ints that uses the previous STL-like allocator.</span>
1739    <span class="keyword">typedef</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">unordered_map</span>
1740       <span class="special">&lt;</span> <span class="identifier">KeyType</span>               <span class="special">,</span> <span class="identifier">MappedType</span>
1741       <span class="special">,</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">hash</span><span class="special">&lt;</span><span class="identifier">KeyType</span><span class="special">&gt;</span>  <span class="special">,</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">equal_to</span><span class="special">&lt;</span><span class="identifier">KeyType</span><span class="special">&gt;</span>
1742       <span class="special">,</span> <span class="identifier">ShmemAllocator</span><span class="special">&gt;</span>
1743    <span class="identifier">MyHashMap</span><span class="special">;</span>
1744
1745    <span class="comment">//Construct a shared memory hash map.</span>
1746    <span class="comment">//Note that the first parameter is the initial bucket count and</span>
1747    <span class="comment">//after that, the hash function, the equality function and the allocator</span>
1748    <span class="identifier">MyHashMap</span> <span class="special">*</span><span class="identifier">myhashmap</span> <span class="special">=</span> <span class="identifier">segment</span><span class="special">.</span><span class="identifier">construct</span><span class="special">&lt;</span><span class="identifier">MyHashMap</span><span class="special">&gt;(</span><span class="string">"MyHashMap"</span><span class="special">)</span>  <span class="comment">//object name</span>
1749       <span class="special">(</span> <span class="number">3</span><span class="special">,</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">hash</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">&gt;(),</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">equal_to</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">&gt;()</span>                  <span class="comment">//</span>
1750       <span class="special">,</span> <span class="identifier">segment</span><span class="special">.</span><span class="identifier">get_allocator</span><span class="special">&lt;</span><span class="identifier">ValueType</span><span class="special">&gt;());</span>                         <span class="comment">//allocator instance</span>
1751
1752    <span class="comment">//Insert data in the hash map</span>
1753    <span class="keyword">for</span><span class="special">(</span><span class="keyword">int</span> <span class="identifier">i</span> <span class="special">=</span> <span class="number">0</span><span class="special">;</span> <span class="identifier">i</span> <span class="special">&lt;</span> <span class="number">100</span><span class="special">;</span> <span class="special">++</span><span class="identifier">i</span><span class="special">){</span>
1754       <span class="identifier">myhashmap</span><span class="special">-&gt;</span><span class="identifier">insert</span><span class="special">(</span><span class="identifier">ValueType</span><span class="special">(</span><span class="identifier">i</span><span class="special">,</span> <span class="special">(</span><span class="keyword">float</span><span class="special">)</span><span class="identifier">i</span><span class="special">));</span>
1755    <span class="special">}</span>
1756    <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span>
1757 <span class="special">}</span>
1758 </pre>
1759 <p>
1760         </p>
1761 </div>
1762 <div class="section">
1763 <div class="titlepage"><div><div><h4 class="title">
1764 <a name="interprocess.allocators_containers.additional_containers.multi_index"></a><a class="link" href="allocators_containers.html#interprocess.allocators_containers.additional_containers.multi_index" title="Boost.MultiIndex containers">Boost.MultiIndex
1765         containers</a>
1766 </h4></div></div></div>
1767 <p>
1768           The widely used <span class="bold"><strong>Boost.MultiIndex</strong></span> library
1769           is compatible with <span class="bold"><strong>Boost.Interprocess</strong></span>
1770           so we can construct pretty good databases in shared memory. Constructing
1771           databases in shared memory is a bit tougher than in normal memory, usually
1772           because those databases contain strings and those strings need to be placed
1773           in shared memory. Shared memory strings require an allocator in their constructors
1774           so this usually makes object insertion a bit more complicated.
1775         </p>
1776 <p>
1777           Here is an example that shows how to put a multi index container in shared
1778           memory:
1779         </p>
1780 <p>
1781 </p>
1782 <pre class="programlisting"><span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">interprocess</span><span class="special">/</span><span class="identifier">managed_shared_memory</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
1783 <span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">interprocess</span><span class="special">/</span><span class="identifier">allocators</span><span class="special">/</span><span class="identifier">allocator</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
1784 <span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">interprocess</span><span class="special">/</span><span class="identifier">containers</span><span class="special">/</span><span class="identifier">string</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
1785
1786
1787 <span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">multi_index_container</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
1788 <span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">multi_index</span><span class="special">/</span><span class="identifier">member</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
1789 <span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">multi_index</span><span class="special">/</span><span class="identifier">ordered_index</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
1790
1791
1792 <span class="keyword">using</span> <span class="keyword">namespace</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">;</span>
1793 <span class="keyword">namespace</span> <span class="identifier">bmi</span> <span class="special">=</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">multi_index</span><span class="special">;</span>
1794
1795 <span class="keyword">typedef</span> <span class="identifier">managed_shared_memory</span><span class="special">::</span><span class="identifier">allocator</span><span class="special">&lt;</span><span class="keyword">char</span><span class="special">&gt;::</span><span class="identifier">type</span>              <span class="identifier">char_allocator</span><span class="special">;</span>
1796 <span class="keyword">typedef</span> <span class="identifier">basic_string</span><span class="special">&lt;</span><span class="keyword">char</span><span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">char_traits</span><span class="special">&lt;</span><span class="keyword">char</span><span class="special">&gt;,</span> <span class="identifier">char_allocator</span><span class="special">&gt;</span><span class="identifier">shm_string</span><span class="special">;</span>
1797
1798 <span class="comment">//Data to insert in shared memory</span>
1799 <span class="keyword">struct</span> <span class="identifier">employee</span>
1800 <span class="special">{</span>
1801    <span class="keyword">int</span>         <span class="identifier">id</span><span class="special">;</span>
1802    <span class="keyword">int</span>         <span class="identifier">age</span><span class="special">;</span>
1803    <span class="identifier">shm_string</span>  <span class="identifier">name</span><span class="special">;</span>
1804    <span class="identifier">employee</span><span class="special">(</span> <span class="keyword">int</span> <span class="identifier">id_</span>
1805            <span class="special">,</span> <span class="keyword">int</span> <span class="identifier">age_</span>
1806            <span class="special">,</span> <span class="keyword">const</span> <span class="keyword">char</span> <span class="special">*</span><span class="identifier">name_</span>
1807            <span class="special">,</span> <span class="keyword">const</span> <span class="identifier">char_allocator</span> <span class="special">&amp;</span><span class="identifier">a</span><span class="special">)</span>
1808       <span class="special">:</span> <span class="identifier">id</span><span class="special">(</span><span class="identifier">id_</span><span class="special">),</span> <span class="identifier">age</span><span class="special">(</span><span class="identifier">age_</span><span class="special">),</span> <span class="identifier">name</span><span class="special">(</span><span class="identifier">name_</span><span class="special">,</span> <span class="identifier">a</span><span class="special">)</span>
1809    <span class="special">{}</span>
1810 <span class="special">};</span>
1811
1812 <span class="comment">//Tags</span>
1813 <span class="keyword">struct</span> <span class="identifier">id</span><span class="special">{};</span>
1814 <span class="keyword">struct</span> <span class="identifier">age</span><span class="special">{};</span>
1815 <span class="keyword">struct</span> <span class="identifier">name</span><span class="special">{};</span>
1816
1817 <span class="comment">// Define a multi_index_container of employees with following indices:</span>
1818 <span class="comment">//   - a unique index sorted by employee::int,</span>
1819 <span class="comment">//   - a non-unique index sorted by employee::name,</span>
1820 <span class="comment">//   - a non-unique index sorted by employee::age.</span>
1821 <span class="keyword">typedef</span> <span class="identifier">bmi</span><span class="special">::</span><span class="identifier">multi_index_container</span><span class="special">&lt;</span>
1822   <span class="identifier">employee</span><span class="special">,</span>
1823   <span class="identifier">bmi</span><span class="special">::</span><span class="identifier">indexed_by</span><span class="special">&lt;</span>
1824     <span class="identifier">bmi</span><span class="special">::</span><span class="identifier">ordered_unique</span>
1825       <span class="special">&lt;</span><span class="identifier">bmi</span><span class="special">::</span><span class="identifier">tag</span><span class="special">&lt;</span><span class="identifier">id</span><span class="special">&gt;,</span>  <span class="identifier">BOOST_MULTI_INDEX_MEMBER</span><span class="special">(</span><span class="identifier">employee</span><span class="special">,</span><span class="keyword">int</span><span class="special">,</span><span class="identifier">id</span><span class="special">)&gt;,</span>
1826     <span class="identifier">bmi</span><span class="special">::</span><span class="identifier">ordered_non_unique</span><span class="special">&lt;</span>
1827       <span class="identifier">bmi</span><span class="special">::</span><span class="identifier">tag</span><span class="special">&lt;</span><span class="identifier">name</span><span class="special">&gt;,</span><span class="identifier">BOOST_MULTI_INDEX_MEMBER</span><span class="special">(</span><span class="identifier">employee</span><span class="special">,</span><span class="identifier">shm_string</span><span class="special">,</span><span class="identifier">name</span><span class="special">)&gt;,</span>
1828     <span class="identifier">bmi</span><span class="special">::</span><span class="identifier">ordered_non_unique</span>
1829       <span class="special">&lt;</span><span class="identifier">bmi</span><span class="special">::</span><span class="identifier">tag</span><span class="special">&lt;</span><span class="identifier">age</span><span class="special">&gt;,</span> <span class="identifier">BOOST_MULTI_INDEX_MEMBER</span><span class="special">(</span><span class="identifier">employee</span><span class="special">,</span><span class="keyword">int</span><span class="special">,</span><span class="identifier">age</span><span class="special">)&gt;</span> <span class="special">&gt;,</span>
1830   <span class="identifier">managed_shared_memory</span><span class="special">::</span><span class="identifier">allocator</span><span class="special">&lt;</span><span class="identifier">employee</span><span class="special">&gt;::</span><span class="identifier">type</span>
1831 <span class="special">&gt;</span> <span class="identifier">employee_set</span><span class="special">;</span>
1832
1833 <span class="keyword">int</span> <span class="identifier">main</span> <span class="special">()</span>
1834 <span class="special">{</span>
1835    <span class="comment">//Remove shared memory on construction and destruction</span>
1836    <span class="keyword">struct</span> <span class="identifier">shm_remove</span>
1837    <span class="special">{</span>
1838       <span class="identifier">shm_remove</span><span class="special">()</span> <span class="special">{</span> <span class="identifier">shared_memory_object</span><span class="special">::</span><span class="identifier">remove</span><span class="special">(</span><span class="string">"MySharedMemory"</span><span class="special">);</span> <span class="special">}</span>
1839       <span class="special">~</span><span class="identifier">shm_remove</span><span class="special">(){</span> <span class="identifier">shared_memory_object</span><span class="special">::</span><span class="identifier">remove</span><span class="special">(</span><span class="string">"MySharedMemory"</span><span class="special">);</span> <span class="special">}</span>
1840    <span class="special">}</span> <span class="identifier">remover</span><span class="special">;</span>
1841
1842    <span class="comment">//Create shared memory</span>
1843    <span class="identifier">managed_shared_memory</span> <span class="identifier">segment</span><span class="special">(</span><span class="identifier">create_only</span><span class="special">,</span><span class="string">"MySharedMemory"</span><span class="special">,</span> <span class="number">65536</span><span class="special">);</span>
1844
1845    <span class="comment">//Construct the multi_index in shared memory</span>
1846    <span class="identifier">employee_set</span> <span class="special">*</span><span class="identifier">es</span> <span class="special">=</span> <span class="identifier">segment</span><span class="special">.</span><span class="identifier">construct</span><span class="special">&lt;</span><span class="identifier">employee_set</span><span class="special">&gt;</span>
1847       <span class="special">(</span><span class="string">"My MultiIndex Container"</span><span class="special">)</span>            <span class="comment">//Container's name in shared memory</span>
1848       <span class="special">(</span> <span class="identifier">employee_set</span><span class="special">::</span><span class="identifier">ctor_args_list</span><span class="special">()</span>
1849       <span class="special">,</span> <span class="identifier">segment</span><span class="special">.</span><span class="identifier">get_allocator</span><span class="special">&lt;</span><span class="identifier">employee</span><span class="special">&gt;());</span>  <span class="comment">//Ctor parameters</span>
1850
1851    <span class="comment">//Now insert elements</span>
1852    <span class="identifier">char_allocator</span> <span class="identifier">ca</span><span class="special">(</span><span class="identifier">segment</span><span class="special">.</span><span class="identifier">get_allocator</span><span class="special">&lt;</span><span class="keyword">char</span><span class="special">&gt;());</span>
1853    <span class="identifier">es</span><span class="special">-&gt;</span><span class="identifier">insert</span><span class="special">(</span><span class="identifier">employee</span><span class="special">(</span><span class="number">0</span><span class="special">,</span><span class="number">31</span><span class="special">,</span> <span class="string">"Joe"</span><span class="special">,</span> <span class="identifier">ca</span><span class="special">));</span>
1854    <span class="identifier">es</span><span class="special">-&gt;</span><span class="identifier">insert</span><span class="special">(</span><span class="identifier">employee</span><span class="special">(</span><span class="number">1</span><span class="special">,</span><span class="number">27</span><span class="special">,</span> <span class="string">"Robert"</span><span class="special">,</span> <span class="identifier">ca</span><span class="special">));</span>
1855    <span class="identifier">es</span><span class="special">-&gt;</span><span class="identifier">insert</span><span class="special">(</span><span class="identifier">employee</span><span class="special">(</span><span class="number">2</span><span class="special">,</span><span class="number">40</span><span class="special">,</span> <span class="string">"John"</span><span class="special">,</span> <span class="identifier">ca</span><span class="special">));</span>
1856    <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span>
1857 <span class="special">}</span>
1858 </pre>
1859 <p>
1860         </p>
1861 </div>
1862 <p>
1863         Programmers can place <span class="bold"><strong>Boost.CircularBuffer</strong></span>
1864         containers in sharecd memory provided they disable debugging facilities with
1865         defines <code class="computeroutput"><span class="identifier">BOOST_CB_DISABLE_DEBUG</span></code>
1866         or the more general <code class="computeroutput"><span class="identifier">NDEBUG</span></code>.
1867         The reason is that those debugging facilities are only compatible with raw
1868         pointers.
1869       </p>
1870 </div>
1871 </div>
1872 <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
1873 <td align="left"></td>
1874 <td align="right"><div class="copyright-footer">Copyright &#169; 2005-2012 Ion Gaztanaga<p>
1875         Distributed under the Boost Software License, Version 1.0. (See accompanying
1876         file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
1877       </p>
1878 </div></td>
1879 </tr></table>
1880 <hr>
1881 <div class="spirit-nav">
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