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  25 </div>
  26 <div class="section">
  27 <div class="titlepage"><div><div><h2 class="title" style="clear: both">
  28 <a name="interprocess.interprocess_smart_ptr"></a><a class="link" href="interprocess_smart_ptr.html" title="Ownership smart pointers">Ownership smart pointers</a>
  29 </h2></div></div></div>
  30 <div class="toc"><dl class="toc">
  31 <dt><span class="section"><a href="interprocess_smart_ptr.html#interprocess.interprocess_smart_ptr.intrusive_ptr">Intrusive
  32       pointer</a></span></dt>
  33 <dt><span class="section"><a href="interprocess_smart_ptr.html#interprocess.interprocess_smart_ptr.scoped_ptr">Scoped
  34       pointer</a></span></dt>
  35 <dt><span class="section"><a href="interprocess_smart_ptr.html#interprocess.interprocess_smart_ptr.shared_ptr">Shared
  36       pointer and weak pointer</a></span></dt>
  37 <dt><span class="section"><a href="interprocess_smart_ptr.html#interprocess.interprocess_smart_ptr.unique_ptr">Unique
  38       pointer</a></span></dt>
  39 </dl></div>
  40 <p>
  41       C++ users know the importance of ownership smart pointers when dealing with
  42       resources. Boost offers a wide range of such type of pointers: <code class="computeroutput"><span class="identifier">intrusive_ptr</span><span class="special">&lt;&gt;</span></code>,
  43       <code class="computeroutput"><span class="identifier">scoped_ptr</span><span class="special">&lt;&gt;</span></code>,
  44       <code class="computeroutput"><span class="identifier">shared_ptr</span><span class="special">&lt;&gt;</span></code>...
  45     </p>
  46 <p>
  47       When building complex shared memory/memory mapped files structures, programmers
  48       would like to use also the advantages of these smart pointers. The problem
  49       is that Boost and C++ TR1 smart pointers are not ready to be used for shared
  50       memory. The cause is that those smart pointers contain raw pointers and they
  51       use virtual functions, something that is not possible if you want to place
  52       your data in shared memory. The virtual function limitation makes even impossible
  53       to achieve the same level of functionality of Boost and TR1 with <span class="bold"><strong>Boost.Interprocess</strong></span> smart pointers.
  54     </p>
  55 <p>
  56       Interprocess ownership smart pointers are mainly "smart pointers containing
  57       smart pointers", so we can specify the pointer type they contain.
  58     </p>
  59 <div class="section">
  60 <div class="titlepage"><div><div><h3 class="title">
  61 <a name="interprocess.interprocess_smart_ptr.intrusive_ptr"></a><a class="link" href="interprocess_smart_ptr.html#interprocess.interprocess_smart_ptr.intrusive_ptr" title="Intrusive pointer">Intrusive
  62       pointer</a>
  63 </h3></div></div></div>
  64 <p>
  65         <code class="computeroutput"><a class="link" href="../boost/interprocess/intrusive_ptr.html" title="Class template intrusive_ptr">boost::interprocess::intrusive_ptr</a></code>
  66         is the generalization of <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">intrusive_ptr</span><span class="special">&lt;&gt;</span></code> to allow non-raw pointers as intrusive
  67         pointer members. As the well-known <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">intrusive_ptr</span></code>
  68         we must specify the pointee type but we also must also specify the pointer
  69         type to be stored in the intrusive_ptr:
  70       </p>
  71 <pre class="programlisting"><span class="comment">//!The intrusive_ptr class template stores a pointer to an object</span>
  72 <span class="comment">//!with an embedded reference count. intrusive_ptr is parameterized on</span>
  73 <span class="comment">//!T (the type of the object pointed to) and VoidPointer(a void pointer type</span>
  74 <span class="comment">//!that defines the type of pointer that intrusive_ptr will store).</span>
  75 <span class="comment">//!intrusive_ptr&lt;T, void *&gt; defines a class with a T* member whereas</span>
  76 <span class="comment">//!intrusive_ptr&lt;T, offset_ptr&lt;void&gt; &gt; defines a class with a offset_ptr&lt;T&gt; member.</span>
  77 <span class="comment">//!Relies on unqualified calls to:</span>
  78 <span class="comment">//!</span>
  79 <span class="comment">//!void intrusive_ptr_add_ref(T * p);</span>
  80 <span class="comment">//!void intrusive_ptr_release(T * p);</span>
  81 <span class="comment">//!</span>
  82 <span class="comment">//!with (p != 0)</span>
  83 <span class="comment">//!</span>
  84 <span class="comment">//!The object is responsible for destroying itself.</span>
  85 <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">VoidPointer</span><span class="special">&gt;</span>
  86 <span class="keyword">class</span> <span class="identifier">intrusive_ptr</span><span class="special">;</span>
  87 </pre>
  88 <p>
  89         So <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">::</span><span class="identifier">intrusive_ptr</span><span class="special">&lt;</span><span class="identifier">MyClass</span><span class="special">,</span> <span class="keyword">void</span><span class="special">*&gt;</span></code>
  90         is equivalent to <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">intrusive_ptr</span><span class="special">&lt;</span><span class="identifier">MyClass</span><span class="special">&gt;</span></code>.
  91         But if we want to place the intrusive_ptr in shared memory we must specify
  92         a relative pointer type like <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">::</span><span class="identifier">intrusive_ptr</span><span class="special">&lt;</span><span class="identifier">MyClass</span><span class="special">,</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">::</span><span class="identifier">offset_ptr</span><span class="special">&lt;</span><span class="keyword">void</span><span class="special">&gt;</span>
  93         <span class="special">&gt;</span></code>
  94       </p>
  95 <p>
  96 </p>
  97 <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>
  98 <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">smart_ptr</span><span class="special">/</span><span class="identifier">intrusive_ptr</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
  99
 100 <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>
 101
 102 <span class="keyword">namespace</span> <span class="identifier">N</span> <span class="special">{</span>
 103
 104 <span class="comment">//A class that has an internal reference count</span>
 105 <span class="keyword">class</span> <span class="identifier">reference_counted_class</span>
 106 <span class="special">{</span>
 107    <span class="keyword">private</span><span class="special">:</span>
 108    <span class="comment">//Non-copyable</span>
 109    <span class="identifier">reference_counted_class</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">reference_counted_class</span>  <span class="special">&amp;);</span>
 110    <span class="comment">//Non-assignable</span>
 111    <span class="identifier">reference_counted_class</span> <span class="special">&amp;</span> <span class="keyword">operator</span><span class="special">=(</span><span class="keyword">const</span> <span class="identifier">reference_counted_class</span> <span class="special">&amp;);</span>
 112    <span class="comment">//A typedef to save typing</span>
 113    <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</span><span class="special">;</span>
 114    <span class="comment">//This is the reference count</span>
 115    <span class="keyword">unsigned</span> <span class="keyword">int</span> <span class="identifier">m_use_count</span><span class="special">;</span>
 116    <span class="comment">//The segment manager allows deletion from shared memory segment</span>
 117    <span class="identifier">offset_ptr</span><span class="special">&lt;</span><span class="identifier">segment_manager</span><span class="special">&gt;</span> <span class="identifier">mp_segment_manager</span><span class="special">;</span>
 118
 119    <span class="keyword">public</span><span class="special">:</span>
 120    <span class="comment">//Constructor</span>
 121    <span class="identifier">reference_counted_class</span><span class="special">(</span><span class="identifier">segment_manager</span> <span class="special">*</span><span class="identifier">s_mngr</span><span class="special">)</span>
 122    <span class="special">:</span> <span class="identifier">m_use_count</span><span class="special">(</span><span class="number">0</span><span class="special">),</span> <span class="identifier">mp_segment_manager</span><span class="special">(</span><span class="identifier">s_mngr</span><span class="special">){}</span>
 123    <span class="comment">//Destructor</span>
 124    <span class="special">~</span><span class="identifier">reference_counted_class</span><span class="special">(){}</span>
 125
 126    <span class="keyword">public</span><span class="special">:</span>
 127    <span class="comment">//Returns the reference count</span>
 128    <span class="keyword">unsigned</span> <span class="keyword">int</span> <span class="identifier">use_count</span><span class="special">()</span> <span class="keyword">const</span>
 129    <span class="special">{</span>  <span class="keyword">return</span> <span class="identifier">m_use_count</span><span class="special">;</span>   <span class="special">}</span>
 130
 131    <span class="comment">//Adds a reference</span>
 132    <span class="keyword">inline</span> <span class="keyword">friend</span> <span class="keyword">void</span> <span class="identifier">intrusive_ptr_add_ref</span><span class="special">(</span><span class="identifier">reference_counted_class</span> <span class="special">*</span> <span class="identifier">p</span><span class="special">)</span>
 133    <span class="special">{</span>  <span class="special">++</span><span class="identifier">p</span><span class="special">-&gt;</span><span class="identifier">m_use_count</span><span class="special">;</span> <span class="special">}</span>
 134
 135    <span class="comment">//Releases a reference</span>
 136    <span class="keyword">inline</span> <span class="keyword">friend</span> <span class="keyword">void</span> <span class="identifier">intrusive_ptr_release</span><span class="special">(</span><span class="identifier">reference_counted_class</span> <span class="special">*</span> <span class="identifier">p</span><span class="special">)</span>
 137    <span class="special">{</span>  <span class="keyword">if</span><span class="special">(--</span><span class="identifier">p</span><span class="special">-&gt;</span><span class="identifier">m_use_count</span> <span class="special">==</span> <span class="number">0</span><span class="special">)</span>  <span class="identifier">p</span><span class="special">-&gt;</span><span class="identifier">mp_segment_manager</span><span class="special">-&gt;</span><span class="identifier">destroy_ptr</span><span class="special">(</span><span class="identifier">p</span><span class="special">);</span> <span class="special">}</span>
 138 <span class="special">};</span>
 139
 140 <span class="special">}</span>  <span class="comment">//namespace N {</span>
 141
 142 <span class="comment">//A class that has an intrusive pointer to reference_counted_class</span>
 143 <span class="keyword">class</span> <span class="identifier">intrusive_ptr_owner</span>
 144 <span class="special">{</span>
 145    <span class="keyword">typedef</span> <span class="identifier">intrusive_ptr</span><span class="special">&lt;</span><span class="identifier">N</span><span class="special">::</span><span class="identifier">reference_counted_class</span><span class="special">,</span>
 146                            <span class="identifier">offset_ptr</span><span class="special">&lt;</span><span class="keyword">void</span><span class="special">&gt;</span> <span class="special">&gt;</span> <span class="identifier">intrusive_ptr_t</span><span class="special">;</span>
 147    <span class="identifier">intrusive_ptr_t</span> <span class="identifier">m_intrusive_ptr</span><span class="special">;</span>
 148
 149    <span class="keyword">public</span><span class="special">:</span>
 150    <span class="comment">//Takes a pointer to the reference counted class</span>
 151    <span class="identifier">intrusive_ptr_owner</span><span class="special">(</span><span class="identifier">N</span><span class="special">::</span><span class="identifier">reference_counted_class</span> <span class="special">*</span><span class="identifier">ptr</span><span class="special">)</span>
 152       <span class="special">:</span> <span class="identifier">m_intrusive_ptr</span><span class="special">(</span><span class="identifier">ptr</span><span class="special">){}</span>
 153 <span class="special">};</span>
 154
 155 <span class="keyword">int</span> <span class="identifier">main</span><span class="special">()</span>
 156 <span class="special">{</span>
 157    <span class="comment">//Remove shared memory on construction and destruction</span>
 158    <span class="keyword">struct</span> <span class="identifier">shm_remove</span>
 159    <span class="special">{</span>
 160       <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>
 161       <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>
 162    <span class="special">}</span> <span class="identifier">remover</span><span class="special">;</span>
 163
 164    <span class="comment">//Create shared memory</span>
 165    <span class="identifier">managed_shared_memory</span> <span class="identifier">shmem</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>
 166
 167    <span class="comment">//Create the unique reference counted object in shared memory</span>
 168    <span class="identifier">N</span><span class="special">::</span><span class="identifier">reference_counted_class</span> <span class="special">*</span><span class="identifier">ref_counted</span> <span class="special">=</span>
 169       <span class="identifier">shmem</span><span class="special">.</span><span class="identifier">construct</span><span class="special">&lt;</span><span class="identifier">N</span><span class="special">::</span><span class="identifier">reference_counted_class</span><span class="special">&gt;</span>
 170          <span class="special">(</span><span class="string">"ref_counted"</span><span class="special">)(</span><span class="identifier">shmem</span><span class="special">.</span><span class="identifier">get_segment_manager</span><span class="special">());</span>
 171
 172    <span class="comment">//Create an array of ten intrusive pointer owners in shared memory</span>
 173    <span class="identifier">intrusive_ptr_owner</span> <span class="special">*</span><span class="identifier">intrusive_owner_array</span> <span class="special">=</span>
 174       <span class="identifier">shmem</span><span class="special">.</span><span class="identifier">construct</span><span class="special">&lt;</span><span class="identifier">intrusive_ptr_owner</span><span class="special">&gt;</span>
 175          <span class="special">(</span><span class="identifier">anonymous_instance</span><span class="special">)[</span><span class="number">10</span><span class="special">](</span><span class="identifier">ref_counted</span><span class="special">);</span>
 176
 177    <span class="comment">//Now test that reference count is ten</span>
 178    <span class="keyword">if</span><span class="special">(</span><span class="identifier">ref_counted</span><span class="special">-&gt;</span><span class="identifier">use_count</span><span class="special">()</span> <span class="special">!=</span> <span class="number">10</span><span class="special">)</span>
 179       <span class="keyword">return</span> <span class="number">1</span><span class="special">;</span>
 180
 181    <span class="comment">//Now destroy the array of intrusive pointer owners</span>
 182    <span class="comment">//This should destroy every intrusive_ptr and because of</span>
 183    <span class="comment">//that reference_counted_class will be destroyed</span>
 184    <span class="identifier">shmem</span><span class="special">.</span><span class="identifier">destroy_ptr</span><span class="special">(</span><span class="identifier">intrusive_owner_array</span><span class="special">);</span>
 185
 186    <span class="comment">//Now the reference counted object should have been destroyed</span>
 187    <span class="keyword">if</span><span class="special">(</span><span class="identifier">shmem</span><span class="special">.</span><span class="identifier">find</span><span class="special">&lt;</span><span class="identifier">intrusive_ptr_owner</span><span class="special">&gt;(</span><span class="string">"ref_counted"</span><span class="special">).</span><span class="identifier">first</span><span class="special">)</span>
 188       <span class="keyword">return</span> <span class="number">1</span><span class="special">;</span>
 189    <span class="comment">//Success!</span>
 190    <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span>
 191 <span class="special">}</span>
 192 </pre>
 193 <p>
 194       </p>
 195 </div>
 196 <div class="section">
 197 <div class="titlepage"><div><div><h3 class="title">
 198 <a name="interprocess.interprocess_smart_ptr.scoped_ptr"></a><a class="link" href="interprocess_smart_ptr.html#interprocess.interprocess_smart_ptr.scoped_ptr" title="Scoped pointer">Scoped
 199       pointer</a>
 200 </h3></div></div></div>
 201 <p>
 202         <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">::</span><span class="identifier">scoped_ptr</span><span class="special">&lt;&gt;</span></code>
 203         is the big brother of <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">scoped_ptr</span><span class="special">&lt;&gt;</span></code>, which adds a custom deleter to specify
 204         how the pointer passed to the scoped_ptr must be destroyed. Also, the <code class="computeroutput"><span class="identifier">pointer</span></code> typedef of the deleter will specify
 205         the pointer type stored by scoped_ptr.
 206       </p>
 207 <pre class="programlisting"><span class="comment">//!scoped_ptr stores a pointer to a dynamically allocated object.</span>
 208 <span class="comment">//!The object pointed to is guaranteed to be deleted, either on destruction</span>
 209 <span class="comment">//!of the scoped_ptr, or via an explicit reset. The user can avoid this</span>
 210 <span class="comment">//!deletion using release().</span>
 211 <span class="comment">//!scoped_ptr is parameterized on T (the type of the object pointed to) and</span>
 212 <span class="comment">//!Deleter (the functor to be executed to delete the internal pointer).</span>
 213 <span class="comment">//!The internal pointer will be of the same pointer type as typename</span>
 214 <span class="comment">//!Deleter::pointer type (that is, if typename Deleter::pointer is</span>
 215 <span class="comment">//!offset_ptr&lt;void&gt;, the internal pointer will be offset_ptr&lt;T&gt;).</span>
 216 <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">Deleter</span><span class="special">&gt;</span>
 217 <span class="keyword">class</span> <span class="identifier">scoped_ptr</span><span class="special">;</span>
 218 </pre>
 219 <p>
 220         <code class="computeroutput"><span class="identifier">scoped_ptr</span><span class="special">&lt;&gt;</span></code>
 221         comes handy to implement <span class="bold"><strong>rollbacks</strong></span> with
 222         exceptions: if an exception is thrown or we call <code class="computeroutput"><span class="keyword">return</span></code>
 223         in the scope of <code class="computeroutput"><span class="identifier">scoped_ptr</span><span class="special">&lt;&gt;</span></code> the deleter is automatically called
 224         so that <span class="bold"><strong>the deleter can be considered as a rollback</strong></span>
 225         function. If all goes well, we call <code class="computeroutput"><span class="identifier">release</span><span class="special">()</span></code> member function to avoid rollback when
 226         the <code class="computeroutput"><span class="identifier">scoped_ptr</span></code> goes out of
 227         scope.
 228       </p>
 229 <p>
 230 </p>
 231 <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>
 232 <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">smart_ptr</span><span class="special">/</span><span class="identifier">scoped_ptr</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
 233
 234 <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>
 235
 236 <span class="keyword">class</span> <span class="identifier">my_class</span>
 237 <span class="special">{};</span>
 238
 239 <span class="keyword">class</span> <span class="identifier">my_exception</span>
 240 <span class="special">{};</span>
 241
 242 <span class="comment">//A functor that destroys the shared memory object</span>
 243 <span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">&gt;</span>
 244 <span class="keyword">class</span> <span class="identifier">my_deleter</span>
 245 <span class="special">{</span>
 246    <span class="keyword">private</span><span class="special">:</span>
 247    <span class="comment">//A typedef to save typing</span>
 248    <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</span><span class="special">;</span>
 249    <span class="comment">//This my_deleter is created in the stack, not in shared memory,</span>
 250    <span class="comment">//so we can use raw pointers</span>
 251    <span class="identifier">segment_manager</span> <span class="special">*</span><span class="identifier">mp_segment_manager</span><span class="special">;</span>
 252
 253    <span class="keyword">public</span><span class="special">:</span>
 254    <span class="comment">//This typedef will specify the pointer type that</span>
 255    <span class="comment">//scoped_ptr will store</span>
 256    <span class="keyword">typedef</span> <span class="identifier">T</span> <span class="special">*</span><span class="identifier">pointer</span><span class="special">;</span>
 257    <span class="comment">//Constructor</span>
 258    <span class="identifier">my_deleter</span><span class="special">(</span><span class="identifier">segment_manager</span> <span class="special">*</span><span class="identifier">s_mngr</span><span class="special">)</span>
 259    <span class="special">:</span> <span class="identifier">mp_segment_manager</span><span class="special">(</span><span class="identifier">s_mngr</span><span class="special">){}</span>
 260
 261    <span class="keyword">void</span> <span class="keyword">operator</span><span class="special">()(</span><span class="identifier">pointer</span> <span class="identifier">object_to_delete</span><span class="special">)</span>
 262    <span class="special">{</span>  <span class="identifier">mp_segment_manager</span><span class="special">-&gt;</span><span class="identifier">destroy_ptr</span><span class="special">(</span><span class="identifier">object_to_delete</span><span class="special">);</span>  <span class="special">}</span>
 263 <span class="special">};</span>
 264
 265 <span class="keyword">int</span> <span class="identifier">main</span> <span class="special">()</span>
 266 <span class="special">{</span>
 267    <span class="comment">//Create shared memory</span>
 268    <span class="comment">//Remove shared memory on construction and destruction</span>
 269    <span class="keyword">struct</span> <span class="identifier">shm_remove</span>
 270    <span class="special">{</span>
 271       <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>
 272       <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>
 273    <span class="special">}</span> <span class="identifier">remover</span><span class="special">;</span>
 274
 275    <span class="identifier">managed_shared_memory</span> <span class="identifier">shmem</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>
 276
 277    <span class="comment">//In the first try, there will be no exceptions</span>
 278    <span class="comment">//in the second try we will throw an exception</span>
 279    <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">2</span><span class="special">;</span> <span class="special">++</span><span class="identifier">i</span><span class="special">){</span>
 280       <span class="comment">//Create an object in shared memory</span>
 281       <span class="identifier">my_class</span> <span class="special">*</span> <span class="identifier">my_object</span> <span class="special">=</span> <span class="identifier">shmem</span><span class="special">.</span><span class="identifier">construct</span><span class="special">&lt;</span><span class="identifier">my_class</span><span class="special">&gt;(</span><span class="string">"my_object"</span><span class="special">)();</span>
 282       <span class="identifier">my_class</span> <span class="special">*</span> <span class="identifier">my_object2</span> <span class="special">=</span> <span class="identifier">shmem</span><span class="special">.</span><span class="identifier">construct</span><span class="special">&lt;</span><span class="identifier">my_class</span><span class="special">&gt;(</span><span class="identifier">anonymous_instance</span><span class="special">)();</span>
 283       <span class="identifier">shmem</span><span class="special">.</span><span class="identifier">destroy_ptr</span><span class="special">(</span><span class="identifier">my_object2</span><span class="special">);</span>
 284
 285       <span class="comment">//Since the next shared memory allocation can throw</span>
 286       <span class="comment">//assign it to a scoped_ptr so that if an exception occurs</span>
 287       <span class="comment">//we destroy the object automatically</span>
 288       <span class="identifier">my_deleter</span><span class="special">&lt;</span><span class="identifier">my_class</span><span class="special">&gt;</span> <span class="identifier">d</span><span class="special">(</span><span class="identifier">shmem</span><span class="special">.</span><span class="identifier">get_segment_manager</span><span class="special">());</span>
 289
 290       <span class="keyword">try</span><span class="special">{</span>
 291          <span class="identifier">scoped_ptr</span><span class="special">&lt;</span><span class="identifier">my_class</span><span class="special">,</span> <span class="identifier">my_deleter</span><span class="special">&lt;</span><span class="identifier">my_class</span><span class="special">&gt;</span> <span class="special">&gt;</span> <span class="identifier">s_ptr</span><span class="special">(</span><span class="identifier">my_object</span><span class="special">,</span> <span class="identifier">d</span><span class="special">);</span>
 292          <span class="comment">//Let's emulate a exception capable operation</span>
 293          <span class="comment">//In the second try, throw an exception</span>
 294          <span class="keyword">if</span><span class="special">(</span><span class="identifier">i</span> <span class="special">==</span> <span class="number">1</span><span class="special">){</span>
 295             <span class="keyword">throw</span><span class="special">(</span><span class="identifier">my_exception</span><span class="special">());</span>
 296          <span class="special">}</span>
 297          <span class="comment">//If we have passed the dangerous zone</span>
 298          <span class="comment">//we can release the scoped pointer</span>
 299          <span class="comment">//to avoid destruction</span>
 300          <span class="identifier">s_ptr</span><span class="special">.</span><span class="identifier">release</span><span class="special">();</span>
 301       <span class="special">}</span>
 302       <span class="keyword">catch</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">my_exception</span> <span class="special">&amp;){}</span>
 303       <span class="comment">//Here, scoped_ptr is destroyed</span>
 304       <span class="comment">//so it we haven't thrown an exception</span>
 305       <span class="comment">//the object should be there, otherwise, destroyed</span>
 306       <span class="keyword">if</span><span class="special">(</span><span class="identifier">i</span> <span class="special">==</span> <span class="number">0</span><span class="special">){</span>
 307          <span class="comment">//Make sure the object is alive</span>
 308          <span class="keyword">if</span><span class="special">(!</span><span class="identifier">shmem</span><span class="special">.</span><span class="identifier">find</span><span class="special">&lt;</span><span class="identifier">my_class</span><span class="special">&gt;(</span><span class="string">"my_object"</span><span class="special">).</span><span class="identifier">first</span><span class="special">){</span>
 309             <span class="keyword">return</span> <span class="number">1</span><span class="special">;</span>
 310          <span class="special">}</span>
 311          <span class="comment">//Now we can use it and delete it manually</span>
 312          <span class="identifier">shmem</span><span class="special">.</span><span class="identifier">destroy</span><span class="special">&lt;</span><span class="identifier">my_class</span><span class="special">&gt;(</span><span class="string">"my_object"</span><span class="special">);</span>
 313       <span class="special">}</span>
 314       <span class="keyword">else</span><span class="special">{</span>
 315          <span class="comment">//Make sure the object has been deleted</span>
 316          <span class="keyword">if</span><span class="special">(</span><span class="identifier">shmem</span><span class="special">.</span><span class="identifier">find</span><span class="special">&lt;</span><span class="identifier">my_class</span><span class="special">&gt;(</span><span class="string">"my_object"</span><span class="special">).</span><span class="identifier">first</span><span class="special">){</span>
 317             <span class="keyword">return</span> <span class="number">1</span><span class="special">;</span>
 318          <span class="special">}</span>
 319       <span class="special">}</span>
 320    <span class="special">}</span>
 321    <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span>
 322 <span class="special">}</span>
 323 </pre>
 324 <p>
 325       </p>
 326 </div>
 327 <div class="section">
 328 <div class="titlepage"><div><div><h3 class="title">
 329 <a name="interprocess.interprocess_smart_ptr.shared_ptr"></a><a class="link" href="interprocess_smart_ptr.html#interprocess.interprocess_smart_ptr.shared_ptr" title="Shared pointer and weak pointer">Shared
 330       pointer and weak pointer</a>
 331 </h3></div></div></div>
 332 <p>
 333         <span class="bold"><strong>Boost.Interprocess</strong></span> also offers the possibility
 334         of creating non-intrusive reference-counted objects in managed shared memory
 335         or mapped files.
 336       </p>
 337 <p>
 338         Unlike <a href="http://www.boost.org/libs/smart_ptr/shared_ptr.htm" target="_top">boost::shared_ptr</a>,
 339         due to limitations of mapped segments <code class="computeroutput"><a class="link" href="../boost/interprocess/shared_ptr.html" title="Class template shared_ptr">boost::interprocess::shared_ptr</a></code>
 340         cannot take advantage of virtual functions to maintain the same shared pointer
 341         type while providing user-defined allocators and deleters. The allocator
 342         and the deleter are template parameters of the shared pointer.
 343       </p>
 344 <p>
 345         Since the reference count and other auxiliary data needed by <code class="computeroutput"><a class="link" href="../boost/interprocess/shared_ptr.html" title="Class template shared_ptr">shared_ptr</a></code>
 346         must be created also in the managed segment, and the deleter has to delete
 347         the object from the segment, the user must specify an allocator object and
 348         a deleter object when constructing a non-empty instance of <code class="computeroutput"><a class="link" href="../boost/interprocess/shared_ptr.html" title="Class template shared_ptr">shared_ptr</a></code>,
 349         just like <span class="bold"><strong>Boost.Interprocess</strong></span> containers
 350         need to pass allocators in their constructors.
 351       </p>
 352 <p>
 353         Here is the declaration of <code class="computeroutput"><a class="link" href="../boost/interprocess/shared_ptr.html" title="Class template shared_ptr">shared_ptr</a></code>:
 354       </p>
 355 <pre class="programlisting"><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">VoidAllocator</span><span class="special">,</span> <span class="keyword">class</span> <span class="identifier">Deleter</span><span class="special">&gt;</span>
 356 <span class="keyword">class</span> <span class="identifier">shared_ptr</span><span class="special">;</span>
 357 </pre>
 358 <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
 359 <li class="listitem">
 360             T is the type of the pointed type.
 361           </li>
 362 <li class="listitem">
 363             VoidAllocator is the allocator to be used to allocate auxiliary elements
 364             such as the reference count, the deleter... The internal <code class="computeroutput"><span class="identifier">pointer</span></code> typedef of the allocator will
 365             determine the type of pointer that shared_ptr will internally use, so
 366             allocators defining <code class="computeroutput"><span class="identifier">pointer</span></code>
 367             as <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>
 368             will make all internal pointers used by <code class="computeroutput"><span class="identifier">shared_ptr</span></code>
 369             to be also relative pointers. See <code class="computeroutput"><a class="link" href="../boost/interprocess/allocator.html" title="Class template allocator">boost::interprocess::allocator</a></code>
 370             for a working allocator.
 371           </li>
 372 <li class="listitem">
 373             Deleter is the function object that will be used to destroy the pointed
 374             object when the last reference to the object is destroyed. The deleter
 375             functor will take a pointer to T of the same category as the void pointer
 376             defined by <code class="computeroutput"><span class="identifier">VoidAllocator</span><span class="special">::</span><span class="identifier">pointer</span></code>.
 377             See <code class="computeroutput"><a class="link" href="../boost/interprocess/deleter.html" title="Class template deleter">boost::interprocess::deleter</a></code>
 378             for a generic deleter that erases a object from a managed segment.
 379           </li>
 380 </ul></div>
 381 <p>
 382         With correctly specified parameters, <span class="bold"><strong>Boost.Interprocess</strong></span>
 383         users can create objects in shared memory that hold shared pointers pointing
 384         to other objects also in shared memory, obtaining the benefits of reference
 385         counting. Let's see how to create a shared pointer in a managed shared memory:
 386       </p>
 387 <p>
 388 </p>
 389 <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>
 390 <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">smart_ptr</span><span class="special">/</span><span class="identifier">shared_ptr</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
 391 <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>
 392 <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">smart_ptr</span><span class="special">/</span><span class="identifier">deleter</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
 393 <span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">cassert</span><span class="special">&gt;</span>
 394
 395 <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>
 396
 397 <span class="comment">//This is type of the object we want to share</span>
 398 <span class="keyword">class</span> <span class="identifier">MyType</span>
 399 <span class="special">{};</span>
 400
 401 <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_type</span><span class="special">;</span>
 402 <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_type</span><span class="special">&gt;</span>  <span class="identifier">void_allocator_type</span><span class="special">;</span>
 403 <span class="keyword">typedef</span> <span class="identifier">deleter</span><span class="special">&lt;</span><span class="identifier">MyType</span><span class="special">,</span> <span class="identifier">segment_manager_type</span><span class="special">&gt;</span>  <span class="identifier">deleter_type</span><span class="special">;</span>
 404 <span class="keyword">typedef</span> <span class="identifier">shared_ptr</span><span class="special">&lt;</span><span class="identifier">MyType</span><span class="special">,</span> <span class="identifier">void_allocator_type</span><span class="special">,</span> <span class="identifier">deleter_type</span><span class="special">&gt;</span> <span class="identifier">my_shared_ptr</span><span class="special">;</span>
 405
 406 <span class="keyword">int</span> <span class="identifier">main</span> <span class="special">()</span>
 407 <span class="special">{</span>
 408    <span class="comment">//Remove shared memory on construction and destruction</span>
 409    <span class="keyword">struct</span> <span class="identifier">shm_remove</span>
 410    <span class="special">{</span>
 411       <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>
 412       <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>
 413    <span class="special">}</span> <span class="identifier">remover</span><span class="special">;</span>
 414
 415    <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">4096</span><span class="special">);</span>
 416
 417    <span class="comment">//Create a shared pointer in shared memory</span>
 418    <span class="comment">//pointing to a newly created object in the segment</span>
 419    <span class="identifier">my_shared_ptr</span> <span class="special">&amp;</span><span class="identifier">shared_ptr_instance</span> <span class="special">=</span>
 420       <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">my_shared_ptr</span><span class="special">&gt;(</span><span class="string">"shared ptr"</span><span class="special">)</span>
 421          <span class="comment">//Arguments to construct the shared pointer</span>
 422          <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">MyType</span><span class="special">&gt;(</span><span class="string">"object to share"</span><span class="special">)()</span>      <span class="comment">//object to own</span>
 423          <span class="special">,</span> <span class="identifier">void_allocator_type</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="comment">//allocator</span>
 424          <span class="special">,</span> <span class="identifier">deleter_type</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="comment">//deleter</span>
 425          <span class="special">);</span>
 426    <span class="identifier">assert</span><span class="special">(</span><span class="identifier">shared_ptr_instance</span><span class="special">.</span><span class="identifier">use_count</span><span class="special">()</span> <span class="special">==</span> <span class="number">1</span><span class="special">);</span>
 427
 428    <span class="comment">//Destroy "shared ptr". "object to share" will be automatically destroyed</span>
 429    <span class="identifier">segment</span><span class="special">.</span><span class="identifier">destroy_ptr</span><span class="special">(&amp;</span><span class="identifier">shared_ptr_instance</span><span class="special">);</span>
 430
 431    <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span>
 432 <span class="special">}</span>
 433 </pre>
 434 <p>
 435       </p>
 436 <p>
 437         <code class="computeroutput"><a class="link" href="../boost/interprocess/shared_ptr.html" title="Class template shared_ptr">boost::interprocess::shared_ptr</a></code>
 438         is very flexible and configurable (we can specify the allocator and the deleter,
 439         for example), but as shown the creation of a shared pointer in managed segments
 440         need too much typing.
 441       </p>
 442 <p>
 443         To simplify this usage, <code class="computeroutput"><a class="link" href="../boost/interprocess/shared_ptr.html" title="Class template shared_ptr">boost::interprocess::shared_ptr</a></code>
 444         header offers a shared pointer definition helper class (<code class="computeroutput"><a class="link" href="../boost/interprocess/managed_shared_ptr.html" title="Struct template managed_shared_ptr">managed_shared_ptr</a></code>)
 445         and a function (<code class="computeroutput"><a class="link" href="../boost/interprocess/make_man_idm45336640970288.html" title="Function template make_managed_shared_ptr">make_managed_shared_ptr</a></code>)
 446         to easily construct a shared pointer from a type allocated in a managed segment
 447         with an allocator that will allocate the reference count also in the managed
 448         segment and a deleter that will erase the object from the segment.
 449       </p>
 450 <p>
 451         These utilities will use a <span class="bold"><strong>Boost.Interprocess</strong></span>
 452         allocator (<code class="computeroutput"><a class="link" href="../boost/interprocess/allocator.html" title="Class template allocator">boost::interprocess::allocator</a></code>)
 453         and deleter (<code class="computeroutput"><a class="link" href="../boost/interprocess/deleter.html" title="Class template deleter">boost::interprocess::deleter</a></code>)
 454         to do their job. The definition of the previous shared pointer could be simplified
 455         to the following:
 456       </p>
 457 <pre class="programlisting"><span class="keyword">typedef</span> <span class="identifier">managed_shared_ptr</span><span class="special">&lt;</span><span class="identifier">MyType</span><span class="special">,</span> <span class="identifier">managed_shared_memory</span><span class="special">&gt;::</span><span class="identifier">type</span> <span class="identifier">my_shared_ptr</span><span class="special">;</span>
 458 </pre>
 459 <p>
 460         And the creation of a shared pointer can be simplified to this:
 461       </p>
 462 <pre class="programlisting"><span class="identifier">my_shared_ptr</span> <span class="identifier">sh_ptr</span> <span class="special">=</span> <span class="identifier">make_managed_shared_ptr</span>
 463    <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">MyType</span><span class="special">&gt;(</span><span class="string">"object to share"</span><span class="special">)(),</span> <span class="identifier">segment</span><span class="special">);</span>
 464 </pre>
 465 <p>
 466         <span class="bold"><strong>Boost.Interprocess</strong></span> also offers a weak pointer
 467         named <code class="computeroutput"><a class="link" href="../boost/interprocess/weak_ptr.html" title="Class template weak_ptr">weak_ptr</a></code>
 468         (with its corresponding <code class="computeroutput"><a class="link" href="../boost/interprocess/managed_weak_ptr.html" title="Struct template managed_weak_ptr">managed_weak_ptr</a></code>
 469         and <code class="computeroutput"><a class="link" href="../boost/interprocess/make_managed_weak_ptr.html" title="Function template make_managed_weak_ptr">make_managed_weak_ptr</a></code>
 470         utilities) to implement non-owning observers of an object owned by <code class="computeroutput"><a class="link" href="../boost/interprocess/shared_ptr.html" title="Class template shared_ptr">shared_ptr</a></code>.
 471       </p>
 472 <p>
 473         Now let's see a detailed example of the use of <code class="computeroutput"><a class="link" href="../boost/interprocess/shared_ptr.html" title="Class template shared_ptr">shared_ptr</a></code>:
 474         and <code class="computeroutput"><a class="link" href="../boost/interprocess/weak_ptr.html" title="Class template weak_ptr">weak_ptr</a></code>
 475       </p>
 476 <p>
 477 </p>
 478 <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_mapped_file</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
 479 <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">smart_ptr</span><span class="special">/</span><span class="identifier">shared_ptr</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
 480 <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">smart_ptr</span><span class="special">/</span><span class="identifier">weak_ptr</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
 481 <span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">cassert</span><span class="special">&gt;</span>
 482
 483 <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>
 484
 485 <span class="comment">//This is type of the object we want to share</span>
 486 <span class="keyword">struct</span> <span class="identifier">type_to_share</span>
 487 <span class="special">{};</span>
 488
 489 <span class="comment">//This is the type of a shared pointer to the previous type</span>
 490 <span class="comment">//that will be built in the mapped file</span>
 491 <span class="keyword">typedef</span> <span class="identifier">managed_shared_ptr</span><span class="special">&lt;</span><span class="identifier">type_to_share</span><span class="special">,</span> <span class="identifier">managed_mapped_file</span><span class="special">&gt;::</span><span class="identifier">type</span> <span class="identifier">shared_ptr_type</span><span class="special">;</span>
 492 <span class="keyword">typedef</span> <span class="identifier">managed_weak_ptr</span><span class="special">&lt;</span><span class="identifier">type_to_share</span><span class="special">,</span> <span class="identifier">managed_mapped_file</span><span class="special">&gt;::</span><span class="identifier">type</span>   <span class="identifier">weak_ptr_type</span><span class="special">;</span>
 493
 494 <span class="comment">//This is a type holding a shared pointer</span>
 495 <span class="keyword">struct</span> <span class="identifier">shared_ptr_owner</span>
 496 <span class="special">{</span>
 497    <span class="identifier">shared_ptr_owner</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">shared_ptr_type</span> <span class="special">&amp;</span><span class="identifier">other_shared_ptr</span><span class="special">)</span>
 498       <span class="special">:</span> <span class="identifier">shared_ptr_</span><span class="special">(</span><span class="identifier">other_shared_ptr</span><span class="special">)</span>
 499    <span class="special">{}</span>
 500
 501    <span class="identifier">shared_ptr_owner</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">shared_ptr_owner</span> <span class="special">&amp;</span><span class="identifier">other_owner</span><span class="special">)</span>
 502       <span class="special">:</span> <span class="identifier">shared_ptr_</span><span class="special">(</span><span class="identifier">other_owner</span><span class="special">.</span><span class="identifier">shared_ptr_</span><span class="special">)</span>
 503    <span class="special">{}</span>
 504
 505    <span class="identifier">shared_ptr_type</span> <span class="identifier">shared_ptr_</span><span class="special">;</span>
 506    <span class="comment">//...</span>
 507 <span class="special">};</span>
 508
 509 <span class="keyword">int</span> <span class="identifier">main</span> <span class="special">()</span>
 510 <span class="special">{</span>
 511    <span class="comment">//Define file names</span>
 512    <span class="keyword">const</span> <span class="keyword">char</span> <span class="special">*</span><span class="identifier">MappedFile</span>  <span class="special">=</span> <span class="string">"MyMappedFile"</span><span class="special">;</span>
 513
 514    <span class="comment">//Destroy any previous file with the name to be used.</span>
 515    <span class="keyword">struct</span> <span class="identifier">file_remove</span>
 516    <span class="special">{</span>
 517       <span class="identifier">file_remove</span><span class="special">(</span><span class="keyword">const</span> <span class="keyword">char</span> <span class="special">*</span><span class="identifier">MappedFile</span><span class="special">)</span>
 518          <span class="special">:</span> <span class="identifier">MappedFile_</span><span class="special">(</span><span class="identifier">MappedFile</span><span class="special">)</span> <span class="special">{</span> <span class="identifier">file_mapping</span><span class="special">::</span><span class="identifier">remove</span><span class="special">(</span><span class="identifier">MappedFile_</span><span class="special">);</span> <span class="special">}</span>
 519       <span class="special">~</span><span class="identifier">file_remove</span><span class="special">(){</span> <span class="identifier">file_mapping</span><span class="special">::</span><span class="identifier">remove</span><span class="special">(</span><span class="identifier">MappedFile_</span><span class="special">);</span> <span class="special">}</span>
 520       <span class="keyword">const</span> <span class="keyword">char</span> <span class="special">*</span><span class="identifier">MappedFile_</span><span class="special">;</span>
 521    <span class="special">}</span> <span class="identifier">remover</span><span class="special">(</span><span class="identifier">MappedFile</span><span class="special">);</span>
 522    <span class="special">{</span>
 523       <span class="identifier">managed_mapped_file</span> <span class="identifier">file</span><span class="special">(</span><span class="identifier">create_only</span><span class="special">,</span> <span class="identifier">MappedFile</span><span class="special">,</span> <span class="number">65536</span><span class="special">);</span>
 524
 525       <span class="comment">//Construct the shared type in the file and</span>
 526       <span class="comment">//pass ownership to this local shared pointer</span>
 527       <span class="identifier">shared_ptr_type</span> <span class="identifier">local_shared_ptr</span> <span class="special">=</span> <span class="identifier">make_managed_shared_ptr</span>
 528          <span class="special">(</span><span class="identifier">file</span><span class="special">.</span><span class="identifier">construct</span><span class="special">&lt;</span><span class="identifier">type_to_share</span><span class="special">&gt;(</span><span class="string">"object to share"</span><span class="special">)(),</span> <span class="identifier">file</span><span class="special">);</span>
 529       <span class="identifier">assert</span><span class="special">(</span><span class="identifier">local_shared_ptr</span><span class="special">.</span><span class="identifier">use_count</span><span class="special">()</span> <span class="special">==</span> <span class="number">1</span><span class="special">);</span>
 530
 531       <span class="comment">//Share ownership of the object between local_shared_ptr and a new "owner1"</span>
 532       <span class="identifier">shared_ptr_owner</span> <span class="special">*</span><span class="identifier">owner1</span> <span class="special">=</span>
 533          <span class="identifier">file</span><span class="special">.</span><span class="identifier">construct</span><span class="special">&lt;</span><span class="identifier">shared_ptr_owner</span><span class="special">&gt;(</span><span class="string">"owner1"</span><span class="special">)(</span><span class="identifier">local_shared_ptr</span><span class="special">);</span>
 534       <span class="identifier">assert</span><span class="special">(</span><span class="identifier">local_shared_ptr</span><span class="special">.</span><span class="identifier">use_count</span><span class="special">()</span> <span class="special">==</span> <span class="number">2</span><span class="special">);</span>
 535
 536       <span class="comment">//local_shared_ptr releases object ownership</span>
 537       <span class="identifier">local_shared_ptr</span><span class="special">.</span><span class="identifier">reset</span><span class="special">();</span>
 538       <span class="identifier">assert</span><span class="special">(</span><span class="identifier">local_shared_ptr</span><span class="special">.</span><span class="identifier">use_count</span><span class="special">()</span> <span class="special">==</span> <span class="number">0</span><span class="special">);</span>
 539       <span class="identifier">assert</span><span class="special">(</span><span class="identifier">owner1</span><span class="special">-&gt;</span><span class="identifier">shared_ptr_</span><span class="special">.</span><span class="identifier">use_count</span><span class="special">()</span> <span class="special">==</span> <span class="number">1</span><span class="special">);</span>
 540
 541       <span class="comment">//Share ownership of the object between "owner1" and a new "owner2"</span>
 542       <span class="identifier">shared_ptr_owner</span> <span class="special">*</span><span class="identifier">owner2</span> <span class="special">=</span>
 543          <span class="identifier">file</span><span class="special">.</span><span class="identifier">construct</span><span class="special">&lt;</span><span class="identifier">shared_ptr_owner</span><span class="special">&gt;(</span><span class="string">"owner2"</span><span class="special">)(*</span><span class="identifier">owner1</span><span class="special">);</span>
 544       <span class="identifier">assert</span><span class="special">(</span><span class="identifier">owner1</span><span class="special">-&gt;</span><span class="identifier">shared_ptr_</span><span class="special">.</span><span class="identifier">use_count</span><span class="special">()</span> <span class="special">==</span> <span class="number">2</span><span class="special">);</span>
 545       <span class="identifier">assert</span><span class="special">(</span><span class="identifier">owner2</span><span class="special">-&gt;</span><span class="identifier">shared_ptr_</span><span class="special">.</span><span class="identifier">use_count</span><span class="special">()</span> <span class="special">==</span> <span class="number">2</span><span class="special">);</span>
 546       <span class="identifier">assert</span><span class="special">(</span><span class="identifier">owner1</span><span class="special">-&gt;</span><span class="identifier">shared_ptr_</span><span class="special">.</span><span class="identifier">get</span><span class="special">()</span> <span class="special">==</span> <span class="identifier">owner2</span><span class="special">-&gt;</span><span class="identifier">shared_ptr_</span><span class="special">.</span><span class="identifier">get</span><span class="special">());</span>
 547       <span class="comment">//The mapped file is unmapped here. Objects have been flushed to disk</span>
 548    <span class="special">}</span>
 549    <span class="special">{</span>
 550       <span class="comment">//Reopen the mapped file and find again all owners</span>
 551       <span class="identifier">managed_mapped_file</span> <span class="identifier">file</span><span class="special">(</span><span class="identifier">open_only</span><span class="special">,</span> <span class="identifier">MappedFile</span><span class="special">);</span>
 552
 553       <span class="identifier">shared_ptr_owner</span> <span class="special">*</span><span class="identifier">owner1</span> <span class="special">=</span> <span class="identifier">file</span><span class="special">.</span><span class="identifier">find</span><span class="special">&lt;</span><span class="identifier">shared_ptr_owner</span><span class="special">&gt;(</span><span class="string">"owner1"</span><span class="special">).</span><span class="identifier">first</span><span class="special">;</span>
 554       <span class="identifier">shared_ptr_owner</span> <span class="special">*</span><span class="identifier">owner2</span> <span class="special">=</span> <span class="identifier">file</span><span class="special">.</span><span class="identifier">find</span><span class="special">&lt;</span><span class="identifier">shared_ptr_owner</span><span class="special">&gt;(</span><span class="string">"owner2"</span><span class="special">).</span><span class="identifier">first</span><span class="special">;</span>
 555       <span class="identifier">assert</span><span class="special">(</span><span class="identifier">owner1</span> <span class="special">&amp;&amp;</span> <span class="identifier">owner2</span><span class="special">);</span>
 556
 557       <span class="comment">//Check everything is as expected</span>
 558       <span class="identifier">assert</span><span class="special">(</span><span class="identifier">file</span><span class="special">.</span><span class="identifier">find</span><span class="special">&lt;</span><span class="identifier">type_to_share</span><span class="special">&gt;(</span><span class="string">"object to share"</span><span class="special">).</span><span class="identifier">first</span> <span class="special">!=</span> <span class="number">0</span><span class="special">);</span>
 559       <span class="identifier">assert</span><span class="special">(</span><span class="identifier">owner1</span><span class="special">-&gt;</span><span class="identifier">shared_ptr_</span><span class="special">.</span><span class="identifier">use_count</span><span class="special">()</span> <span class="special">==</span> <span class="number">2</span><span class="special">);</span>
 560       <span class="identifier">assert</span><span class="special">(</span><span class="identifier">owner2</span><span class="special">-&gt;</span><span class="identifier">shared_ptr_</span><span class="special">.</span><span class="identifier">use_count</span><span class="special">()</span> <span class="special">==</span> <span class="number">2</span><span class="special">);</span>
 561       <span class="identifier">assert</span><span class="special">(</span><span class="identifier">owner1</span><span class="special">-&gt;</span><span class="identifier">shared_ptr_</span><span class="special">.</span><span class="identifier">get</span><span class="special">()</span> <span class="special">==</span> <span class="identifier">owner2</span><span class="special">-&gt;</span><span class="identifier">shared_ptr_</span><span class="special">.</span><span class="identifier">get</span><span class="special">());</span>
 562
 563       <span class="comment">//Now destroy one of the owners, the reference count drops.</span>
 564       <span class="identifier">file</span><span class="special">.</span><span class="identifier">destroy_ptr</span><span class="special">(</span><span class="identifier">owner1</span><span class="special">);</span>
 565       <span class="identifier">assert</span><span class="special">(</span><span class="identifier">owner2</span><span class="special">-&gt;</span><span class="identifier">shared_ptr_</span><span class="special">.</span><span class="identifier">use_count</span><span class="special">()</span> <span class="special">==</span> <span class="number">1</span><span class="special">);</span>
 566
 567       <span class="comment">//Create a weak pointer</span>
 568       <span class="identifier">weak_ptr_type</span> <span class="identifier">local_observer1</span><span class="special">(</span><span class="identifier">owner2</span><span class="special">-&gt;</span><span class="identifier">shared_ptr_</span><span class="special">);</span>
 569       <span class="identifier">assert</span><span class="special">(</span><span class="identifier">local_observer1</span><span class="special">.</span><span class="identifier">use_count</span><span class="special">()</span> <span class="special">==</span> <span class="identifier">owner2</span><span class="special">-&gt;</span><span class="identifier">shared_ptr_</span><span class="special">.</span><span class="identifier">use_count</span><span class="special">());</span>
 570
 571       <span class="special">{</span>  <span class="comment">//Create a local shared pointer from the weak pointer</span>
 572       <span class="identifier">shared_ptr_type</span> <span class="identifier">local_shared_ptr</span> <span class="special">=</span> <span class="identifier">local_observer1</span><span class="special">.</span><span class="identifier">lock</span><span class="special">();</span>
 573       <span class="identifier">assert</span><span class="special">(</span><span class="identifier">local_observer1</span><span class="special">.</span><span class="identifier">use_count</span><span class="special">()</span> <span class="special">==</span> <span class="identifier">owner2</span><span class="special">-&gt;</span><span class="identifier">shared_ptr_</span><span class="special">.</span><span class="identifier">use_count</span><span class="special">());</span>
 574       <span class="identifier">assert</span><span class="special">(</span><span class="identifier">local_observer1</span><span class="special">.</span><span class="identifier">use_count</span><span class="special">()</span> <span class="special">==</span> <span class="number">2</span><span class="special">);</span>
 575       <span class="special">}</span>
 576
 577       <span class="comment">//Now destroy the remaining owner. "object to share" will be destroyed</span>
 578       <span class="identifier">file</span><span class="special">.</span><span class="identifier">destroy_ptr</span><span class="special">(</span><span class="identifier">owner2</span><span class="special">);</span>
 579       <span class="identifier">assert</span><span class="special">(</span><span class="identifier">file</span><span class="special">.</span><span class="identifier">find</span><span class="special">&lt;</span><span class="identifier">type_to_share</span><span class="special">&gt;(</span><span class="string">"object to share"</span><span class="special">).</span><span class="identifier">first</span> <span class="special">==</span> <span class="number">0</span><span class="special">);</span>
 580
 581       <span class="comment">//Test observer</span>
 582       <span class="identifier">assert</span><span class="special">(</span><span class="identifier">local_observer1</span><span class="special">.</span><span class="identifier">expired</span><span class="special">());</span>
 583       <span class="identifier">assert</span><span class="special">(</span><span class="identifier">local_observer1</span><span class="special">.</span><span class="identifier">use_count</span><span class="special">()</span> <span class="special">==</span> <span class="number">0</span><span class="special">);</span>
 584
 585       <span class="comment">//The reference count will be deallocated when all weak pointers</span>
 586       <span class="comment">//disappear. After that, the file is unmapped.</span>
 587    <span class="special">}</span>
 588    <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span>
 589 <span class="special">}</span>
 590 </pre>
 591 <p>
 592       </p>
 593 <p>
 594         In general, using <span class="bold"><strong>Boost.Interprocess</strong></span>' <code class="computeroutput"><a class="link" href="../boost/interprocess/shared_ptr.html" title="Class template shared_ptr">shared_ptr</a></code> and <code class="computeroutput"><a class="link" href="../boost/interprocess/weak_ptr.html" title="Class template weak_ptr">weak_ptr</a></code> is very similar
 595         to their counterparts <a href="http://www.boost.org/libs/smart_ptr/shared_ptr.htm" target="_top">boost::shared_ptr</a>
 596         and <a href="http://www.boost.org/libs/smart_ptr/weak_ptr.htm" target="_top">boost::weak_ptr</a>,
 597         but they need more template parameters and more run-time parameters in their
 598         constructors.
 599       </p>
 600 <p>
 601         Just like <a href="http://www.boost.org/libs/smart_ptr/shared_ptr.htm" target="_top">boost::shared_ptr</a>
 602         can be stored in a STL container, <code class="computeroutput"><a class="link" href="../boost/interprocess/shared_ptr.html" title="Class template shared_ptr">shared_ptr</a></code>
 603         can also be stored in <span class="bold"><strong>Boost.Interprocess</strong></span>
 604         containers.
 605       </p>
 606 <p>
 607         If a programmer just uses <code class="computeroutput"><a class="link" href="../boost/interprocess/shared_ptr.html" title="Class template shared_ptr">shared_ptr</a></code>
 608         to be able to insert dynamically constructed objects into a container constructed
 609         in the managed segment, but he does not need to share the ownership of that
 610         object with other objects <code class="computeroutput"><a class="link" href="../boost/interprocess/managed_unique_ptr.html" title="Struct template managed_unique_ptr">managed_unique_ptr</a></code>
 611         is a much faster and easier to use alternative.
 612       </p>
 613 </div>
 614 <div class="section">
 615 <div class="titlepage"><div><div><h3 class="title">
 616 <a name="interprocess.interprocess_smart_ptr.unique_ptr"></a><a class="link" href="interprocess_smart_ptr.html#interprocess.interprocess_smart_ptr.unique_ptr" title="Unique pointer">Unique
 617       pointer</a>
 618 </h3></div></div></div>
 619 <p>
 620         Unique ownership smart pointers are really useful to free programmers from
 621         manual resource liberation of non-shared objects. <span class="bold"><strong>Boost.Interprocess</strong></span>'
 622         <code class="computeroutput"><span class="identifier">unique_ptr</span></code> is much like
 623         <code class="computeroutput"><a class="link" href="../boost/interprocess/scoped_ptr.html" title="Class template scoped_ptr">scoped_ptr</a></code> but
 624         it's <span class="bold"><strong>moveable</strong></span> and can be easily inserted
 625         in <span class="bold"><strong>Boost.Interprocess</strong></span> containers. Interprocess
 626         had its own <code class="computeroutput"><span class="identifier">unique_ptr</span></code> implementation
 627         but from Boost 1.57, <span class="bold"><strong>Boost.Interprocess</strong></span>
 628         uses the improved and generic <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">unique_ptr</span></code>
 629         implementation. Here is the declaration of the unique pointer class:
 630       </p>
 631 <pre class="programlisting"><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">D</span><span class="special">&gt;</span>
 632 <span class="keyword">class</span> <span class="identifier">unique_ptr</span><span class="special">;</span>
 633 </pre>
 634 <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
 635 <li class="listitem">
 636             T is the type of the object pointed by <code class="computeroutput"><span class="identifier">unique_ptr</span></code>.
 637           </li>
 638 <li class="listitem">
 639             D is the deleter that will erase the object type of the object pointed
 640             by the unique_ptr when the unique pointer is destroyed (and if still
 641             has the ownership of the object). If the deleter defines an internal
 642             <code class="computeroutput"><span class="identifier">pointer</span></code> typedef, <code class="computeroutput"><span class="identifier">unique_ptr</span></code>] will use an internal pointer
 643             of the same type. So if <code class="computeroutput"><span class="identifier">D</span><span class="special">::</span><span class="identifier">pointer</span></code>
 644             is <code class="computeroutput"><span class="identifier">offset_ptr</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span></code>
 645             the unique pointer will store a relative pointer instead of a raw one.
 646             This allows placing <code class="computeroutput"><span class="identifier">unique_ptr</span></code>
 647             in shared memory and memory-mapped files.
 648           </li>
 649 </ul></div>
 650 <p>
 651         <code class="computeroutput"><span class="identifier">unique_ptr</span></code> can release the
 652         ownership of the stored pointer so it's useful also to be used as a rollback
 653         function. One of the main properties of the class is that <span class="bold"><strong>is
 654         not copyable, but only moveable</strong></span>. When a unique pointer is moved
 655         to another one, the ownership of the pointer is transferred from the source
 656         unique pointer to the target unique pointer. If the target unique pointer
 657         owned an object, that object is first deleted before taking ownership of
 658         the new object.
 659       </p>
 660 <p>
 661         <span class="bold"><strong>Boost.Interprocess</strong></span> also offers auxiliary
 662         types to easily define and construct unique pointers that can be placed in
 663         managed segments and will correctly delete owned object from the segment:
 664         <code class="computeroutput"><a class="link" href="../boost/interprocess/managed_unique_ptr.html" title="Struct template managed_unique_ptr">managed_unique_ptr</a></code>
 665         and <code class="computeroutput"><a class="link" href="../boost/interprocess/make_managed_unique_ptr.html" title="Function template make_managed_unique_ptr">make_managed_unique_ptr</a></code>
 666         utilities.
 667       </p>
 668 <p>
 669         Here we see an example of the use <code class="computeroutput"><span class="identifier">unique_ptr</span></code>
 670         including creating containers of such objects:
 671       </p>
 672 <p>
 673 </p>
 674 <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_mapped_file</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
 675 <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">smart_ptr</span><span class="special">/</span><span class="identifier">unique_ptr</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
 676 <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>
 677 <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>
 678 <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>
 679 <span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">cassert</span><span class="special">&gt;</span>
 680
 681 <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>
 682
 683 <span class="comment">//This is type of the object we'll allocate dynamically</span>
 684 <span class="keyword">struct</span> <span class="identifier">MyType</span>
 685 <span class="special">{</span>
 686    <span class="identifier">MyType</span><span class="special">(</span><span class="keyword">int</span> <span class="identifier">number</span> <span class="special">=</span> <span class="number">0</span><span class="special">)</span>
 687       <span class="special">:</span>  <span class="identifier">number_</span><span class="special">(</span><span class="identifier">number</span><span class="special">)</span>
 688    <span class="special">{}</span>
 689    <span class="keyword">int</span> <span class="identifier">number_</span><span class="special">;</span>
 690 <span class="special">};</span>
 691
 692 <span class="comment">//This is the type of a unique pointer to the previous type</span>
 693 <span class="comment">//that will be built in the mapped file</span>
 694 <span class="keyword">typedef</span> <span class="identifier">managed_unique_ptr</span><span class="special">&lt;</span><span class="identifier">MyType</span><span class="special">,</span> <span class="identifier">managed_mapped_file</span><span class="special">&gt;::</span><span class="identifier">type</span> <span class="identifier">unique_ptr_type</span><span class="special">;</span>
 695
 696 <span class="comment">//Define containers of unique pointer. Unique pointer simplifies object management</span>
 697 <span class="keyword">typedef</span> <span class="identifier">vector</span>
 698    <span class="special">&lt;</span> <span class="identifier">unique_ptr_type</span>
 699    <span class="special">,</span> <span class="identifier">allocator</span><span class="special">&lt;</span><span class="identifier">unique_ptr_type</span><span class="special">,</span> <span class="identifier">managed_mapped_file</span><span class="special">::</span><span class="identifier">segment_manager</span><span class="special">&gt;</span>
 700    <span class="special">&gt;</span> <span class="identifier">unique_ptr_vector_t</span><span class="special">;</span>
 701
 702 <span class="keyword">typedef</span> <span class="identifier">list</span>
 703    <span class="special">&lt;</span> <span class="identifier">unique_ptr_type</span>
 704    <span class="special">,</span> <span class="identifier">allocator</span><span class="special">&lt;</span><span class="identifier">unique_ptr_type</span><span class="special">,</span> <span class="identifier">managed_mapped_file</span><span class="special">::</span><span class="identifier">segment_manager</span><span class="special">&gt;</span>
 705    <span class="special">&gt;</span> <span class="identifier">unique_ptr_list_t</span><span class="special">;</span>
 706
 707 <span class="keyword">int</span> <span class="identifier">main</span> <span class="special">()</span>
 708 <span class="special">{</span>
 709    <span class="comment">//Define file names</span>
 710    <span class="keyword">const</span> <span class="keyword">char</span> <span class="special">*</span><span class="identifier">MappedFile</span>  <span class="special">=</span> <span class="string">"MyMappedFile"</span><span class="special">;</span>
 711
 712    <span class="comment">//Destroy any previous file with the name to be used.</span>
 713    <span class="keyword">struct</span> <span class="identifier">file_remove</span>
 714    <span class="special">{</span>
 715       <span class="identifier">file_remove</span><span class="special">(</span><span class="keyword">const</span> <span class="keyword">char</span> <span class="special">*</span><span class="identifier">MappedFile</span><span class="special">)</span>
 716          <span class="special">:</span> <span class="identifier">MappedFile_</span><span class="special">(</span><span class="identifier">MappedFile</span><span class="special">)</span> <span class="special">{</span> <span class="identifier">file_mapping</span><span class="special">::</span><span class="identifier">remove</span><span class="special">(</span><span class="identifier">MappedFile_</span><span class="special">);</span> <span class="special">}</span>
 717       <span class="special">~</span><span class="identifier">file_remove</span><span class="special">(){</span> <span class="identifier">file_mapping</span><span class="special">::</span><span class="identifier">remove</span><span class="special">(</span><span class="identifier">MappedFile_</span><span class="special">);</span> <span class="special">}</span>
 718       <span class="keyword">const</span> <span class="keyword">char</span> <span class="special">*</span><span class="identifier">MappedFile_</span><span class="special">;</span>
 719    <span class="special">}</span> <span class="identifier">remover</span><span class="special">(</span><span class="identifier">MappedFile</span><span class="special">);</span>
 720    <span class="special">{</span>
 721       <span class="identifier">managed_mapped_file</span> <span class="identifier">file</span><span class="special">(</span><span class="identifier">create_only</span><span class="special">,</span> <span class="identifier">MappedFile</span><span class="special">,</span> <span class="number">65536</span><span class="special">);</span>
 722
 723       <span class="comment">//Construct an object in the file and</span>
 724       <span class="comment">//pass ownership to this local unique pointer</span>
 725       <span class="identifier">unique_ptr_type</span> <span class="identifier">local_unique_ptr</span> <span class="special">(</span><span class="identifier">make_managed_unique_ptr</span>
 726          <span class="special">(</span><span class="identifier">file</span><span class="special">.</span><span class="identifier">construct</span><span class="special">&lt;</span><span class="identifier">MyType</span><span class="special">&gt;(</span><span class="string">"unique object"</span><span class="special">)(),</span> <span class="identifier">file</span><span class="special">));</span>
 727       <span class="identifier">assert</span><span class="special">(</span><span class="identifier">local_unique_ptr</span><span class="special">.</span><span class="identifier">get</span><span class="special">()</span> <span class="special">!=</span> <span class="number">0</span><span class="special">);</span>
 728
 729       <span class="comment">//Reset the unique pointer. The object is automatically destroyed</span>
 730       <span class="identifier">local_unique_ptr</span><span class="special">.</span><span class="identifier">reset</span><span class="special">();</span>
 731       <span class="identifier">assert</span><span class="special">(</span><span class="identifier">file</span><span class="special">.</span><span class="identifier">find</span><span class="special">&lt;</span><span class="identifier">MyType</span><span class="special">&gt;(</span><span class="string">"unique object"</span><span class="special">).</span><span class="identifier">first</span> <span class="special">==</span> <span class="number">0</span><span class="special">);</span>
 732
 733       <span class="comment">//Now create a vector of unique pointers</span>
 734       <span class="identifier">unique_ptr_vector_t</span> <span class="special">*</span><span class="identifier">unique_vector</span> <span class="special">=</span>
 735          <span class="identifier">file</span><span class="special">.</span><span class="identifier">construct</span><span class="special">&lt;</span><span class="identifier">unique_ptr_vector_t</span><span class="special">&gt;(</span><span class="string">"unique vector"</span><span class="special">)(</span><span class="identifier">file</span><span class="special">.</span><span class="identifier">get_segment_manager</span><span class="special">());</span>
 736
 737       <span class="comment">//Speed optimization</span>
 738       <span class="identifier">unique_vector</span><span class="special">-&gt;</span><span class="identifier">reserve</span><span class="special">(</span><span class="number">100</span><span class="special">);</span>
 739
 740       <span class="comment">//Now insert all values</span>
 741       <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>
 742          <span class="identifier">unique_ptr_type</span> <span class="identifier">p</span><span class="special">(</span><span class="identifier">make_managed_unique_ptr</span><span class="special">(</span><span class="identifier">file</span><span class="special">.</span><span class="identifier">construct</span><span class="special">&lt;</span><span class="identifier">MyType</span><span class="special">&gt;(</span><span class="identifier">anonymous_instance</span><span class="special">)(</span><span class="identifier">i</span><span class="special">),</span> <span class="identifier">file</span><span class="special">));</span>
 743          <span class="identifier">unique_vector</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">p</span><span class="special">));</span>
 744          <span class="identifier">assert</span><span class="special">(</span><span class="identifier">unique_vector</span><span class="special">-&gt;</span><span class="identifier">back</span><span class="special">()-&gt;</span><span class="identifier">number_</span> <span class="special">==</span> <span class="identifier">i</span><span class="special">);</span>
 745       <span class="special">}</span>
 746
 747       <span class="comment">//Now create a list of unique pointers</span>
 748       <span class="identifier">unique_ptr_list_t</span> <span class="special">*</span><span class="identifier">unique_list</span> <span class="special">=</span>
 749          <span class="identifier">file</span><span class="special">.</span><span class="identifier">construct</span><span class="special">&lt;</span><span class="identifier">unique_ptr_list_t</span><span class="special">&gt;(</span><span class="string">"unique list"</span><span class="special">)(</span><span class="identifier">file</span><span class="special">.</span><span class="identifier">get_segment_manager</span><span class="special">());</span>
 750
 751       <span class="comment">//Pass ownership of all values to the list</span>
 752       <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">99</span><span class="special">;</span> <span class="special">!</span><span class="identifier">unique_vector</span><span class="special">-&gt;</span><span class="identifier">empty</span><span class="special">();</span> <span class="special">--</span><span class="identifier">i</span><span class="special">){</span>
 753          <span class="identifier">unique_list</span><span class="special">-&gt;</span><span class="identifier">push_front</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">unique_vector</span><span class="special">-&gt;</span><span class="identifier">back</span><span class="special">()));</span>
 754          <span class="comment">//The unique ptr of the vector is now empty...</span>
 755          <span class="identifier">assert</span><span class="special">(</span><span class="identifier">unique_vector</span><span class="special">-&gt;</span><span class="identifier">back</span><span class="special">()</span> <span class="special">==</span> <span class="number">0</span><span class="special">);</span>
 756          <span class="identifier">unique_vector</span><span class="special">-&gt;</span><span class="identifier">pop_back</span><span class="special">();</span>
 757          <span class="comment">//...and the list has taken ownership of the value</span>
 758          <span class="identifier">assert</span><span class="special">(</span><span class="identifier">unique_list</span><span class="special">-&gt;</span><span class="identifier">front</span><span class="special">()</span> <span class="special">!=</span> <span class="number">0</span><span class="special">);</span>
 759          <span class="identifier">assert</span><span class="special">(</span><span class="identifier">unique_list</span><span class="special">-&gt;</span><span class="identifier">front</span><span class="special">()-&gt;</span><span class="identifier">number_</span> <span class="special">==</span> <span class="identifier">i</span><span class="special">);</span>
 760       <span class="special">}</span>
 761       <span class="identifier">assert</span><span class="special">(</span><span class="identifier">unique_list</span><span class="special">-&gt;</span><span class="identifier">size</span><span class="special">()</span> <span class="special">==</span> <span class="number">100</span><span class="special">);</span>
 762
 763       <span class="comment">//Now destroy the empty vector.</span>
 764       <span class="identifier">file</span><span class="special">.</span><span class="identifier">destroy_ptr</span><span class="special">(</span><span class="identifier">unique_vector</span><span class="special">);</span>
 765       <span class="comment">//The mapped file is unmapped here. Objects have been flushed to disk</span>
 766    <span class="special">}</span>
 767    <span class="special">{</span>
 768       <span class="comment">//Reopen the mapped file and find again the list</span>
 769       <span class="identifier">managed_mapped_file</span> <span class="identifier">file</span><span class="special">(</span><span class="identifier">open_only</span><span class="special">,</span> <span class="identifier">MappedFile</span><span class="special">);</span>
 770
 771       <span class="identifier">unique_ptr_list_t</span>   <span class="special">*</span><span class="identifier">unique_list</span> <span class="special">=</span>
 772          <span class="identifier">file</span><span class="special">.</span><span class="identifier">find</span><span class="special">&lt;</span><span class="identifier">unique_ptr_list_t</span><span class="special">&gt;(</span><span class="string">"unique list"</span><span class="special">).</span><span class="identifier">first</span><span class="special">;</span>
 773       <span class="identifier">assert</span><span class="special">(</span><span class="identifier">unique_list</span><span class="special">);</span>
 774       <span class="identifier">assert</span><span class="special">(</span><span class="identifier">unique_list</span><span class="special">-&gt;</span><span class="identifier">size</span><span class="special">()</span> <span class="special">==</span> <span class="number">100</span><span class="special">);</span>
 775
 776       <span class="identifier">unique_ptr_list_t</span><span class="special">::</span><span class="identifier">const_iterator</span> <span class="identifier">list_it</span> <span class="special">=</span> <span class="identifier">unique_list</span><span class="special">-&gt;</span><span class="identifier">begin</span><span class="special">();</span>
 777       <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> <span class="special">++</span><span class="identifier">list_it</span><span class="special">){</span>
 778          <span class="identifier">assert</span><span class="special">((*</span><span class="identifier">list_it</span><span class="special">)-&gt;</span><span class="identifier">number_</span> <span class="special">==</span> <span class="identifier">i</span><span class="special">);</span>
 779       <span class="special">}</span>
 780
 781       <span class="comment">//Now destroy the list. All elements will be automatically deallocated.</span>
 782       <span class="identifier">file</span><span class="special">.</span><span class="identifier">destroy_ptr</span><span class="special">(</span><span class="identifier">unique_list</span><span class="special">);</span>
 783    <span class="special">}</span>
 784    <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span>
 785 <span class="special">}</span>
 786 </pre>
 787 <p>
 788       </p>
 789 </div>
 790 </div>
 791 <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
 792 <td align="left"></td>
 793 <td align="right"><div class="copyright-footer">Copyright &#169; 2005-2015 Ion Gaztanaga<p>
 794         Distributed under the Boost Software License, Version 1.0. (See accompanying
 795         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>)
 796       </p>
 797 </div></td>
 798 </tr></table>
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