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  26 <div class="titlepage"><div><div><h2 class="title" style="clear: both">
  27 <a name="context.ecv2"></a><a name="ecv2"></a><a class="link" href="ecv2.html" title="Class execution_context (version 2)">Class execution_context
  28     (version 2)</a>
  29 </h2></div></div></div>
  30 <div class="note"><table border="0" summary="Note">
  31 <tr>
  32 <td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../../doc/src/images/note.png"></td>
  33 <th align="left">Note</th>
  34 </tr>
  35 <tr><td align="left" valign="top"><p>
  36         <span class="emphasis"><em>execution_context</em></span> (v2) is the reference implementation
  37         of C++ proposal <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2016/p0099r1.pdf" target="_top">P099R1:
  38         A low-level API for stackful context switching</a>.
  39       </p></td></tr>
  40 </table></div>
  41 <div class="note"><table border="0" summary="Note">
  42 <tr>
  43 <td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../../doc/src/images/note.png"></td>
  44 <th align="left">Note</th>
  45 </tr>
  46 <tr><td align="left" valign="top"><p>
  47         <span class="emphasis"><em>execution_context</em></span> (v2) resides in the inlined sub-namespace
  48         <code class="computeroutput"><span class="identifier">v2</span></code>.
  49       </p></td></tr>
  50 </table></div>
  51 <div class="note"><table border="0" summary="Note">
  52 <tr>
  53 <td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../../doc/src/images/note.png"></td>
  54 <th align="left">Note</th>
  55 </tr>
  56 <tr><td align="left" valign="top"><p>
  57         Segmented stacks (<span class="emphasis"><em>segmented-stacks=on</em></span>), e.g. on demand
  58         growing stacks, are not supported by <span class="emphasis"><em>execution_context</em></span>
  59         (v2).
  60       </p></td></tr>
  61 </table></div>
  62 <p>
  63       Class <span class="emphasis"><em>execution_context</em></span> encapsulates context switching
  64       and manages the associated context' stack (allocation/deallocation).
  65     </p>
  66 <p>
  67       <span class="emphasis"><em>execution_context</em></span> allocates the context stack (using its
  68       <a class="link" href="stack.html#stack"><span class="emphasis"><em>StackAllocator</em></span></a> argument)
  69       and creates a control structure on top of it. This structure is responsible
  70       for managing context' stack. The address of the control structure is stored
  71       in the first frame of context' stack (e.g. it can not directly accessed from
  72       within <span class="emphasis"><em>execution_context</em></span>). In contrast to <a class="link" href="ecv1.html#ecv1"><span class="emphasis"><em>execution_context</em></span>
  73       (v1)</a> the ownership of the control structure is not shared (no member
  74       variable to control structure in <span class="emphasis"><em>execution_context</em></span>).
  75       <span class="emphasis"><em>execution_context</em></span> keeps internally a state that is moved
  76       by a call of <span class="emphasis"><em>execution_context::operator()</em></span> (<code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> will be
  77       invalidated), e.g. after a calling <span class="emphasis"><em>execution_context::operator()</em></span>,
  78       <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>
  79       can not be used for an additional context switch.
  80     </p>
  81 <p>
  82       <span class="emphasis"><em>execution_context</em></span> is only move-constructible and move-assignable.
  83     </p>
  84 <p>
  85       The moved state is assigned to a new instance of <span class="emphasis"><em>execution_context</em></span>.
  86       This object becomes the first argument of the context-function, if the context
  87       was resumed the first time, or the first element in a tuple returned by <span class="emphasis"><em>execution_context::operator()</em></span>
  88       that has been called in the resumed context. In contrast to <a class="link" href="ecv1.html#ecv1"><span class="emphasis"><em>execution_context</em></span>
  89       (v1)</a>, the context switch is faster because no global pointer etc. is
  90       involved.
  91     </p>
  92 <div class="important"><table border="0" summary="Important">
  93 <tr>
  94 <td rowspan="2" align="center" valign="top" width="25"><img alt="[Important]" src="../../../../../doc/src/images/important.png"></td>
  95 <th align="left">Important</th>
  96 </tr>
  97 <tr><td align="left" valign="top"><p>
  98         Segmented stacks are not supported by <span class="emphasis"><em>execution_context</em></span>
  99         (v2).
 100       </p></td></tr>
 101 </table></div>
 102 <p>
 103       On return the context-function of the current context has to specify an <span class="emphasis"><em>execution_context</em></span>
 104       to which the execution control is transferred after termination of the current
 105       context.
 106     </p>
 107 <p>
 108       If an instance with valid state goes out of scope and the context-function
 109       has not yet returned, the stack is traversed in order to access the control
 110       structure (address stored at the first stack frame) and context' stack is deallocated
 111       via the <span class="emphasis"><em>StackAllocator</em></span>. The stack walking makes the destruction
 112       of <span class="emphasis"><em>execution_context</em></span> slow and should be prevented if possible.
 113     </p>
 114 <p>
 115       <span class="emphasis"><em>execution_context</em></span> expects a <span class="emphasis"><em>context-function</em></span>
 116       with signature <code class="computeroutput"><span class="identifier">execution_context</span><span class="special">(</span><span class="identifier">execution_context</span>
 117       <span class="identifier">ctx</span><span class="special">,</span> <span class="identifier">Args</span> <span class="special">...</span> <span class="identifier">args</span><span class="special">)</span></code>. The
 118       parameter <code class="computeroutput"><span class="identifier">ctx</span></code> represents the
 119       context from which this context was resumed (e.g. that has called <span class="emphasis"><em>execution_context::operator()</em></span>
 120       on <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>)
 121       and <code class="computeroutput"><span class="identifier">args</span></code> are the data passed
 122       to <span class="emphasis"><em>execution_context::operator()</em></span>. The return value represents
 123       the execution_context that has to be resumed, after termiantion of this context.
 124     </p>
 125 <p>
 126       Benefits of <a class="link" href="ecv2.html#ecv2"><span class="emphasis"><em>execution_context</em></span> (v2)</a>
 127       over <a class="link" href="ecv1.html#ecv1"><span class="emphasis"><em>execution_context</em></span> (v1)</a>
 128       are: faster context switch, type-safety of passed/returned arguments.
 129     </p>
 130 <h4>
 131 <a name="context.ecv2.h0"></a>
 132       <span><a name="context.ecv2.usage_of__emphasis_execution_context__emphasis_"></a></span><a class="link" href="ecv2.html#context.ecv2.usage_of__emphasis_execution_context__emphasis_">usage
 133       of <span class="emphasis"><em>execution_context</em></span></a>
 134     </h4>
 135 <pre class="programlisting"><span class="keyword">int</span> <span class="identifier">n</span><span class="special">=</span><span class="number">35</span><span class="special">;</span>
 136 <span class="identifier">ctx</span><span class="special">::</span><span class="identifier">execution_context</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">&gt;</span> <span class="identifier">source</span><span class="special">(</span>
 137     <span class="special">[</span><span class="identifier">n</span><span class="special">](</span><span class="identifier">ctx</span><span class="special">::</span><span class="identifier">execution_context</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">&gt;</span> <span class="special">&amp;&amp;</span> <span class="identifier">sink</span><span class="special">,</span><span class="keyword">int</span><span class="special">)</span> <span class="keyword">mutable</span> <span class="special">{</span>
 138         <span class="keyword">int</span> <span class="identifier">a</span><span class="special">=</span><span class="number">0</span><span class="special">;</span>
 139         <span class="keyword">int</span> <span class="identifier">b</span><span class="special">=</span><span class="number">1</span><span class="special">;</span>
 140         <span class="keyword">while</span><span class="special">(</span><span class="identifier">n</span><span class="special">--&gt;</span><span class="number">0</span><span class="special">){</span>
 141             <span class="keyword">auto</span> <span class="identifier">result</span><span class="special">=</span><span class="identifier">sink</span><span class="special">(</span><span class="identifier">a</span><span class="special">);</span>
 142             <span class="identifier">sink</span><span class="special">=</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">get</span><span class="special">&lt;</span><span class="number">0</span><span class="special">&gt;(</span><span class="identifier">result</span><span class="special">));</span>
 143             <span class="keyword">auto</span> <span class="identifier">next</span><span class="special">=</span><span class="identifier">a</span><span class="special">+</span><span class="identifier">b</span><span class="special">;</span>
 144             <span class="identifier">a</span><span class="special">=</span><span class="identifier">b</span><span class="special">;</span>
 145             <span class="identifier">b</span><span class="special">=</span><span class="identifier">next</span><span class="special">;</span>
 146         <span class="special">}</span>
 147         <span class="keyword">return</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">sink</span><span class="special">);</span>
 148     <span class="special">});</span>
 149 <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">10</span><span class="special">;++</span><span class="identifier">i</span><span class="special">){</span>
 150     <span class="keyword">auto</span> <span class="identifier">result</span><span class="special">=</span><span class="identifier">source</span><span class="special">(</span><span class="identifier">i</span><span class="special">);</span>
 151     <span class="identifier">source</span><span class="special">=</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">get</span><span class="special">&lt;</span><span class="number">0</span><span class="special">&gt;(</span><span class="identifier">result</span><span class="special">));</span>
 152     <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span><span class="special">&lt;&lt;</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">get</span><span class="special">&lt;</span><span class="number">1</span><span class="special">&gt;(</span><span class="identifier">result</span><span class="special">)&lt;&lt;</span><span class="string">" "</span><span class="special">;</span>
 153 <span class="special">}</span>
 154
 155 <span class="identifier">output</span><span class="special">:</span>
 156     <span class="number">0</span> <span class="number">1</span> <span class="number">1</span> <span class="number">2</span> <span class="number">3</span> <span class="number">5</span> <span class="number">8</span> <span class="number">13</span> <span class="number">21</span> <span class="number">34</span>
 157 </pre>
 158 <p>
 159       This simple example demonstrates the basic usage of <span class="emphasis"><em>execution_context</em></span>
 160       as a generator. The context <code class="computeroutput"><span class="identifier">sink</span></code>
 161       represents the <span class="emphasis"><em>main</em></span>-context (function <span class="emphasis"><em>main()</em></span>
 162       running). <code class="computeroutput"><span class="identifier">sink</span></code> is generated
 163       by the framework (first element of lambda's parameter list). Because the state
 164       is invalidated (== changed) by each call of <span class="emphasis"><em>execution_context::operator()</em></span>,
 165       the new state of the <span class="emphasis"><em>execution_context</em></span>, returned by <span class="emphasis"><em>execution_context::operator()</em></span>,
 166       needs to be assigned to <code class="computeroutput"><span class="identifier">sink</span></code>
 167       after each call.
 168     </p>
 169 <p>
 170       The lambda that calculates the Fibonacci numbers is executed inside the context
 171       represented by <code class="computeroutput"><span class="identifier">source</span></code>. Calculated
 172       Fibonacci numbers are transferred between the two context' via expression
 173       <span class="emphasis"><em>sink(a)</em></span> (and returned by <span class="emphasis"><em>source()</em></span>).
 174       Note that this example represents a <span class="emphasis"><em>generator</em></span> thus the
 175       value transferred into the lambda via <span class="emphasis"><em>source()</em></span> is not
 176       used. Using <span class="emphasis"><em>boost::optional&lt;&gt;</em></span> as transferred type,
 177       might also appropriate to express this fact.
 178     </p>
 179 <p>
 180       The locale variables <code class="computeroutput"><span class="identifier">a</span></code>, <code class="computeroutput"><span class="identifier">b</span></code> and <code class="computeroutput"> <span class="identifier">next</span></code>
 181       remain their values during each context switch (<span class="emphasis"><em>yield(a)</em></span>).
 182       This is possible due <code class="computeroutput"><span class="identifier">source</span></code>
 183       has its own stack and the stack is exchanged by each context switch.
 184     </p>
 185 <h4>
 186 <a name="context.ecv2.h1"></a>
 187       <span><a name="context.ecv2.parameter_passing"></a></span><a class="link" href="ecv2.html#context.ecv2.parameter_passing">parameter
 188       passing</a>
 189     </h4>
 190 <p>
 191       With <code class="computeroutput"><span class="identifier">execution_context</span><span class="special">&lt;</span><span class="keyword">void</span><span class="special">&gt;</span></code> no
 192       data will be transferred, only the context switch is executed.
 193     </p>
 194 <pre class="programlisting"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">context</span><span class="special">::</span><span class="identifier">execution_context</span><span class="special">&lt;</span><span class="keyword">void</span><span class="special">&gt;</span> <span class="identifier">ctx1</span><span class="special">([](</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">context</span><span class="special">::</span><span class="identifier">execution_context</span><span class="special">&lt;</span><span class="keyword">void</span><span class="special">&gt;</span> <span class="special">&amp;&amp;</span> <span class="identifier">ctx2</span><span class="special">){</span>
 195             <span class="identifier">std</span><span class="special">::</span><span class="identifier">printf</span><span class="special">(</span><span class="string">"inside ctx1\n"</span><span class="special">);</span>
 196             <span class="keyword">return</span> <span class="identifier">ctx2</span><span class="special">();</span>
 197         <span class="special">});</span>
 198 <span class="identifier">ctx1</span><span class="special">();</span>
 199
 200 <span class="identifier">output</span><span class="special">:</span>
 201     <span class="identifier">inside</span> <span class="identifier">ctx1</span>
 202 </pre>
 203 <p>
 204       <code class="computeroutput"><span class="identifier">ctx1</span><span class="special">()</span></code>
 205       resumes <code class="computeroutput"><span class="identifier">ctx1</span></code>, e.g. the lambda
 206       passed at the constructor of <code class="computeroutput"><span class="identifier">ctx1</span></code>
 207       is entered. Argument <code class="computeroutput"><span class="identifier">ctx2</span></code> represents
 208       the context that has been suspended with the invocation of <code class="computeroutput"><span class="identifier">ctx1</span><span class="special">()</span></code>. When the lambda returns <code class="computeroutput"><span class="identifier">ctx2</span></code>,
 209       context <code class="computeroutput"><span class="identifier">ctx1</span></code> will be terminated
 210       while the context represented by <code class="computeroutput"><span class="identifier">ctx2</span></code>
 211       is resumed, hence the control of execution returns from <code class="computeroutput"><span class="identifier">ctx1</span><span class="special">()</span></code>.
 212     </p>
 213 <p>
 214       The arguments passed to <span class="emphasis"><em>execution_context::operator()</em></span>,
 215       in one context, is passed as the last arguments of the <span class="emphasis"><em>context-function</em></span>
 216       if the context is started for the first time. In all following invocations
 217       of <span class="emphasis"><em>execution_context::operator()</em></span> the arguments passed
 218       to <span class="emphasis"><em>execution_context::operator()</em></span>, in one context, is returned
 219       by <span class="emphasis"><em>execution_context::operator()</em></span> in the other context.
 220     </p>
 221 <pre class="programlisting"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">context</span><span class="special">::</span><span class="identifier">execution_context</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">&gt;</span> <span class="identifier">ctx1</span><span class="special">([](</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">context</span><span class="special">::</span><span class="identifier">execution_context</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">&gt;</span> <span class="special">&amp;&amp;</span> <span class="identifier">ctx2</span><span class="special">,</span><span class="keyword">int</span> <span class="identifier">j</span><span class="special">){</span>
 222             <span class="identifier">std</span><span class="special">::</span><span class="identifier">printf</span><span class="special">(</span><span class="string">"inside ctx1,j==%d\n"</span><span class="special">,</span><span class="identifier">j</span><span class="special">);</span>
 223             <span class="identifier">std</span><span class="special">::</span><span class="identifier">tie</span><span class="special">(</span><span class="identifier">ctx2</span><span class="special">,</span><span class="identifier">j</span><span class="special">)=</span><span class="identifier">ctx2</span><span class="special">(</span><span class="identifier">j</span><span class="special">+</span><span class="number">1</span><span class="special">);</span>
 224             <span class="keyword">return</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">ctx2</span><span class="special">);</span>
 225         <span class="special">});</span>
 226 <span class="keyword">int</span> <span class="identifier">i</span><span class="special">=</span><span class="number">1</span><span class="special">;</span>
 227 <span class="identifier">std</span><span class="special">::</span><span class="identifier">tie</span><span class="special">(</span><span class="identifier">ctx1</span><span class="special">,</span><span class="identifier">i</span><span class="special">)=</span><span class="identifier">ctx1</span><span class="special">(</span><span class="identifier">i</span><span class="special">);</span>
 228 <span class="identifier">std</span><span class="special">::</span><span class="identifier">printf</span><span class="special">(</span><span class="string">"i==%d\n"</span><span class="special">,</span><span class="identifier">i</span><span class="special">);</span>
 229
 230 <span class="identifier">output</span><span class="special">:</span>
 231     <span class="identifier">inside</span> <span class="identifier">ctx1</span><span class="special">,</span><span class="identifier">j</span><span class="special">==</span><span class="number">1</span>
 232     <span class="identifier">i</span><span class="special">==</span><span class="number">2</span>
 233 </pre>
 234 <p>
 235       <code class="computeroutput"><span class="identifier">ctx1</span><span class="special">(</span><span class="identifier">i</span><span class="special">)</span></code> enters
 236       the lambda in context <code class="computeroutput"><span class="identifier">ctx1</span></code>
 237       with argument <code class="computeroutput"><span class="identifier">j</span><span class="special">=</span><span class="number">1</span></code>. The expression <code class="computeroutput"><span class="identifier">ctx2</span><span class="special">(</span><span class="identifier">j</span><span class="special">+</span><span class="number">1</span><span class="special">)</span></code> resumes the
 238       context represented by <code class="computeroutput"><span class="identifier">ctx2</span></code>
 239       and transfers back an integer of <code class="computeroutput"><span class="identifier">j</span><span class="special">+</span><span class="number">1</span></code>. On return
 240       of <code class="computeroutput"><span class="identifier">ctx1</span><span class="special">(</span><span class="identifier">i</span><span class="special">)</span></code>, the variable
 241       <code class="computeroutput"><span class="identifier">i</span></code> contains the value of <code class="computeroutput"><span class="identifier">j</span><span class="special">+</span><span class="number">1</span></code>.
 242     </p>
 243 <p>
 244       If more than one argument has to be transferred, the signature of the context-function
 245       is simply extended.
 246     </p>
 247 <pre class="programlisting"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">context</span><span class="special">::</span><span class="identifier">execution_context</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">,</span><span class="keyword">int</span><span class="special">&gt;</span> <span class="identifier">ctx1</span><span class="special">([](</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">context</span><span class="special">::</span><span class="identifier">execution_context</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">,</span><span class="keyword">int</span><span class="special">&gt;</span> <span class="special">&amp;&amp;</span> <span class="identifier">ctx2</span><span class="special">,</span><span class="keyword">int</span> <span class="identifier">i</span><span class="special">,</span><span class="keyword">int</span> <span class="identifier">j</span><span class="special">){</span>
 248             <span class="identifier">std</span><span class="special">::</span><span class="identifier">printf</span><span class="special">(</span><span class="string">"inside ctx1,i==%d,j==%d\n"</span><span class="special">,</span><span class="identifier">i</span><span class="special">,</span><span class="identifier">j</span><span class="special">);</span>
 249             <span class="identifier">std</span><span class="special">::</span><span class="identifier">tie</span><span class="special">(</span><span class="identifier">ctx2</span><span class="special">,</span><span class="identifier">i</span><span class="special">,</span><span class="identifier">j</span><span class="special">)=</span><span class="identifier">ctx2</span><span class="special">(</span><span class="identifier">i</span><span class="special">+</span><span class="identifier">j</span><span class="special">,</span><span class="identifier">i</span><span class="special">-</span><span class="identifier">j</span><span class="special">);</span>
 250             <span class="keyword">return</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">ctx2</span><span class="special">);</span>
 251         <span class="special">});</span>
 252 <span class="keyword">int</span> <span class="identifier">i</span><span class="special">=</span><span class="number">2</span><span class="special">,</span><span class="identifier">j</span><span class="special">=</span><span class="number">1</span><span class="special">;</span>
 253 <span class="identifier">std</span><span class="special">::</span><span class="identifier">tie</span><span class="special">(</span><span class="identifier">ctx1</span><span class="special">,</span><span class="identifier">i</span><span class="special">,</span><span class="identifier">j</span><span class="special">)=</span><span class="identifier">ctx1</span><span class="special">(</span><span class="identifier">i</span><span class="special">,</span><span class="identifier">j</span><span class="special">);</span>
 254 <span class="identifier">std</span><span class="special">::</span><span class="identifier">printf</span><span class="special">(</span><span class="string">"i==%d,j==%d\n"</span><span class="special">,</span><span class="identifier">i</span><span class="special">,</span><span class="identifier">j</span><span class="special">);</span>
 255
 256 <span class="identifier">output</span><span class="special">:</span>
 257     <span class="identifier">inside</span> <span class="identifier">ctx1</span><span class="special">,</span><span class="identifier">i</span><span class="special">==</span><span class="number">2</span><span class="special">,</span><span class="identifier">j</span><span class="special">==</span><span class="number">1</span>
 258     <span class="identifier">i</span><span class="special">==</span><span class="number">3</span><span class="special">,</span><span class="identifier">j</span><span class="special">==</span><span class="number">1</span>
 259 </pre>
 260 <p>
 261       For use-cases, that require to transfer data of different type in each direction,
 262       <span class="emphasis"><em>boost::variant&lt;&gt;</em></span> could be used.
 263     </p>
 264 <pre class="programlisting"><span class="keyword">class</span> <span class="identifier">X</span><span class="special">{</span>
 265 <span class="keyword">private</span><span class="special">:</span>
 266     <span class="identifier">std</span><span class="special">::</span><span class="identifier">exception_ptr</span> <span class="identifier">excptr_</span><span class="special">;</span>
 267     <span class="identifier">boost</span><span class="special">::</span><span class="identifier">context</span><span class="special">::</span><span class="identifier">execution_context</span><span class="special">&lt;</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">variant</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">,</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">&gt;&gt;</span> <span class="identifier">ctx_</span><span class="special">;</span>
 268
 269 <span class="keyword">public</span><span class="special">:</span>
 270     <span class="identifier">X</span><span class="special">():</span>
 271         <span class="identifier">excptr_</span><span class="special">(),</span>
 272         <span class="identifier">ctx_</span><span class="special">([=](</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">context</span><span class="special">::</span><span class="identifier">execution_context</span><span class="special">&lt;</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">variant</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">,</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">&gt;&gt;</span> <span class="special">&amp;&amp;</span> <span class="identifier">ctx</span><span class="special">,</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">variant</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">,</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">&gt;</span> <span class="identifier">data</span><span class="special">){</span>
 273                 <span class="keyword">try</span> <span class="special">{</span>
 274                     <span class="keyword">for</span> <span class="special">(;;)</span> <span class="special">{</span>
 275                         <span class="keyword">int</span> <span class="identifier">i</span><span class="special">=</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">get</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">&gt;(</span><span class="identifier">data</span><span class="special">);</span>
 276                         <span class="identifier">data</span><span class="special">=</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">lexical_cast</span><span class="special">&lt;</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">&gt;(</span><span class="identifier">i</span><span class="special">);</span>
 277                         <span class="keyword">auto</span> <span class="identifier">result</span><span class="special">=</span><span class="identifier">ctx</span><span class="special">(</span><span class="identifier">data</span><span class="special">);</span>
 278                         <span class="identifier">ctx</span><span class="special">=</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">get</span><span class="special">&lt;</span><span class="number">0</span><span class="special">&gt;(</span><span class="identifier">result</span><span class="special">));</span>
 279                         <span class="identifier">data</span><span class="special">=</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">get</span><span class="special">&lt;</span><span class="number">1</span><span class="special">&gt;(</span><span class="identifier">result</span><span class="special">);</span>
 280                 <span class="special">}</span> <span class="keyword">catch</span> <span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">bad_cast</span> <span class="keyword">const</span><span class="special">&amp;)</span> <span class="special">{</span>
 281                     <span class="identifier">excptr_</span><span class="special">=</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">current_exception</span><span class="special">();</span>
 282                 <span class="special">}</span>
 283                 <span class="keyword">return</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">ctx</span><span class="special">);</span>
 284              <span class="special">})</span>
 285     <span class="special">{}</span>
 286
 287     <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span> <span class="keyword">operator</span><span class="special">()(</span><span class="keyword">int</span> <span class="identifier">i</span><span class="special">){</span>
 288         <span class="identifier">boost</span><span class="special">::</span><span class="identifier">variant</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">,</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">&gt;</span> <span class="identifier">data</span><span class="special">=</span><span class="identifier">i</span><span class="special">;</span>
 289         <span class="keyword">auto</span> <span class="identifier">result</span><span class="special">=</span><span class="identifier">ctx_</span><span class="special">(</span><span class="identifier">data</span><span class="special">);</span>
 290         <span class="identifier">ctx_</span><span class="special">=</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">get</span><span class="special">&lt;</span><span class="number">0</span><span class="special">&gt;(</span><span class="identifier">result</span><span class="special">));</span>
 291         <span class="identifier">data</span><span class="special">=</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">get</span><span class="special">&lt;</span><span class="number">1</span><span class="special">&gt;(</span><span class="identifier">result</span><span class="special">);</span>
 292         <span class="keyword">if</span><span class="special">(</span><span class="identifier">excptr_</span><span class="special">){</span>
 293             <span class="identifier">std</span><span class="special">::</span><span class="identifier">rethrow_exception</span><span class="special">(</span><span class="identifier">excptr_</span><span class="special">);</span>
 294         <span class="special">}</span>
 295         <span class="keyword">return</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">get</span><span class="special">&lt;</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">&gt;(</span><span class="identifier">data</span><span class="special">);</span>
 296     <span class="special">}</span>
 297 <span class="special">};</span>
 298
 299 <span class="identifier">X</span> <span class="identifier">x</span><span class="special">;</span>
 300 <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special">&lt;&lt;</span> <span class="identifier">x</span><span class="special">(</span><span class="number">7</span><span class="special">)</span> <span class="special">&lt;&lt;</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span>
 301
 302 <span class="identifier">output</span><span class="special">:</span>
 303 <span class="number">7</span>
 304 </pre>
 305 <p>
 306       In the case of unidirectional transfer of data, <span class="emphasis"><em>boost::optional&lt;&gt;</em></span>
 307       or a pointer are appropriate.
 308     </p>
 309 <h4>
 310 <a name="context.ecv2.h2"></a>
 311       <span><a name="context.ecv2.exception_handling"></a></span><a class="link" href="ecv2.html#context.ecv2.exception_handling">exception
 312       handling</a>
 313     </h4>
 314 <p>
 315       If the function executed inside a <span class="emphasis"><em>execution_context</em></span> emits
 316       ans exception, the application is terminated by calling <span class="emphasis"><em>std::terminate()</em></span>.
 317       <span class="emphasis"><em>std::exception_ptr</em></span> can be used to transfer exceptions
 318       between different execution contexts.
 319     </p>
 320 <div class="important"><table border="0" summary="Important">
 321 <tr>
 322 <td rowspan="2" align="center" valign="top" width="25"><img alt="[Important]" src="../../../../../doc/src/images/important.png"></td>
 323 <th align="left">Important</th>
 324 </tr>
 325 <tr><td align="left" valign="top"><p>
 326         Do not jump from inside a catch block and then re-throw the exception in
 327         another execution context.
 328       </p></td></tr>
 329 </table></div>
 330 <a name="ecv2_ontop"></a><h4>
 331 <a name="context.ecv2.h3"></a>
 332       <span><a name="context.ecv2.executing_function_on_top_of_a_context"></a></span><a class="link" href="ecv2.html#context.ecv2.executing_function_on_top_of_a_context">Executing
 333       function on top of a context</a>
 334     </h4>
 335 <p>
 336       Sometimes it is useful to execute a new function on top of a resumed context.
 337       For this purpose <span class="emphasis"><em>execution_context::operator()</em></span> with first
 338       argument <code class="computeroutput"><span class="identifier">exec_ontop_arg</span></code> has
 339       to be used. The function passed as argument must return a tuple of execution_context
 340       and arguments.
 341     </p>
 342 <pre class="programlisting"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">context</span><span class="special">::</span><span class="identifier">execution_context</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">&gt;</span> <span class="identifier">f1</span><span class="special">(</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">context</span><span class="special">::</span><span class="identifier">execution_context</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">&gt;</span> <span class="special">&amp;&amp;</span> <span class="identifier">ctx</span><span class="special">,</span><span class="keyword">int</span> <span class="identifier">data</span><span class="special">)</span> <span class="special">{</span>
 343     <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special">&lt;&lt;</span> <span class="string">"f1: entered first time: "</span> <span class="special">&lt;&lt;</span> <span class="identifier">data</span> <span class="special">&lt;&lt;</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span>
 344     <span class="identifier">std</span><span class="special">::</span><span class="identifier">tie</span><span class="special">(</span><span class="identifier">ctx</span><span class="special">,</span><span class="identifier">data</span><span class="special">)=</span><span class="identifier">ctx</span><span class="special">(</span><span class="identifier">data</span><span class="special">+</span><span class="number">1</span><span class="special">);</span>
 345     <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special">&lt;&lt;</span> <span class="string">"f1: entered second time: "</span> <span class="special">&lt;&lt;</span> <span class="identifier">data</span> <span class="special">&lt;&lt;</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span>
 346     <span class="identifier">std</span><span class="special">::</span><span class="identifier">tie</span><span class="special">(</span><span class="identifier">ctx</span><span class="special">,</span><span class="identifier">data</span><span class="special">)=</span><span class="identifier">ctx</span><span class="special">(</span><span class="identifier">data</span><span class="special">+</span><span class="number">1</span><span class="special">);</span>
 347     <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special">&lt;&lt;</span> <span class="string">"f1: entered third time: "</span> <span class="special">&lt;&lt;</span> <span class="identifier">data</span> <span class="special">&lt;&lt;</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span>
 348     <span class="keyword">return</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">ctx</span><span class="special">);</span>
 349 <span class="special">}</span>
 350
 351 <span class="keyword">int</span> <span class="identifier">f2</span><span class="special">(</span><span class="keyword">int</span> <span class="identifier">data</span><span class="special">)</span> <span class="special">{</span>
 352     <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special">&lt;&lt;</span> <span class="string">"f2: entered: "</span> <span class="special">&lt;&lt;</span> <span class="identifier">data</span> <span class="special">&lt;&lt;</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span>
 353     <span class="keyword">return</span> <span class="special">-</span><span class="number">1</span><span class="special">;</span>
 354 <span class="special">}</span>
 355
 356 <span class="keyword">int</span> <span class="identifier">data</span><span class="special">=</span><span class="number">0</span><span class="special">;</span>
 357 <span class="identifier">boost</span><span class="special">::</span><span class="identifier">context</span><span class="special">::</span><span class="identifier">execution_context</span><span class="special">&lt;</span> <span class="keyword">int</span> <span class="special">&gt;</span> <span class="identifier">ctx</span><span class="special">(</span><span class="identifier">f1</span><span class="special">);</span>
 358 <span class="identifier">std</span><span class="special">::</span><span class="identifier">tie</span><span class="special">(</span><span class="identifier">ctx</span><span class="special">,</span><span class="identifier">data</span><span class="special">)=</span><span class="identifier">ctx</span><span class="special">(</span><span class="identifier">data</span><span class="special">+</span><span class="number">1</span><span class="special">);</span>
 359 <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special">&lt;&lt;</span> <span class="string">"f1: returned first time: "</span> <span class="special">&lt;&lt;</span> <span class="identifier">data</span> <span class="special">&lt;&lt;</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span>
 360 <span class="identifier">std</span><span class="special">::</span><span class="identifier">tie</span><span class="special">(</span><span class="identifier">ctx</span><span class="special">,</span><span class="identifier">data</span><span class="special">)=</span><span class="identifier">ctx</span><span class="special">(</span><span class="identifier">data</span><span class="special">+</span><span class="number">1</span><span class="special">);</span>
 361 <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special">&lt;&lt;</span> <span class="string">"f1: returned second time: "</span> <span class="special">&lt;&lt;</span> <span class="identifier">data</span> <span class="special">&lt;&lt;</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span>
 362 <span class="identifier">std</span><span class="special">::</span><span class="identifier">tie</span><span class="special">(</span><span class="identifier">ctx</span><span class="special">,</span><span class="identifier">data</span><span class="special">)=</span><span class="identifier">ctx</span><span class="special">(</span><span class="identifier">ctx</span><span class="special">::</span><span class="identifier">exec_ontop_arg</span><span class="special">,</span><span class="identifier">f2</span><span class="special">,</span><span class="identifier">data</span><span class="special">+</span><span class="number">1</span><span class="special">);</span>
 363
 364 <span class="identifier">output</span><span class="special">:</span>
 365     <span class="identifier">f1</span><span class="special">:</span> <span class="identifier">entered</span> <span class="identifier">first</span> <span class="identifier">time</span><span class="special">:</span> <span class="number">1</span>
 366     <span class="identifier">f1</span><span class="special">:</span> <span class="identifier">returned</span> <span class="identifier">first</span> <span class="identifier">time</span><span class="special">:</span> <span class="number">2</span>
 367     <span class="identifier">f1</span><span class="special">:</span> <span class="identifier">entered</span> <span class="identifier">second</span> <span class="identifier">time</span><span class="special">:</span> <span class="number">3</span>
 368     <span class="identifier">f1</span><span class="special">:</span> <span class="identifier">returned</span> <span class="identifier">second</span> <span class="identifier">time</span><span class="special">:</span> <span class="number">4</span>
 369     <span class="identifier">f2</span><span class="special">:</span> <span class="identifier">entered</span><span class="special">:</span> <span class="number">5</span>
 370     <span class="identifier">f1</span><span class="special">:</span> <span class="identifier">entered</span> <span class="identifier">third</span> <span class="identifier">time</span><span class="special">:</span> <span class="special">-</span><span class="number">1</span>
 371 </pre>
 372 <p>
 373       The expression <code class="computeroutput"><span class="identifier">ctx</span><span class="special">(</span><span class="identifier">ctx</span><span class="special">::</span><span class="identifier">exec_ontop_arg</span><span class="special">,</span><span class="identifier">f2</span><span class="special">,</span><span class="identifier">data</span><span class="special">+</span><span class="number">1</span><span class="special">)</span></code> executes <code class="computeroutput"><span class="identifier">f2</span><span class="special">()</span></code> on top of context <code class="computeroutput"><span class="identifier">ctx</span></code>,
 374       e.g. an additional stack frame is allocated on top of the context stack (in
 375       front of <code class="computeroutput"><span class="identifier">f1</span><span class="special">()</span></code>).
 376       <code class="computeroutput"><span class="identifier">f2</span><span class="special">()</span></code>
 377       returns argument <code class="computeroutput"><span class="special">-</span><span class="number">1</span></code>
 378       that will returned by the second invocation of <code class="computeroutput"><span class="identifier">ctx</span><span class="special">(</span><span class="identifier">data</span><span class="special">+</span><span class="number">1</span><span class="special">)</span></code> in <code class="computeroutput"><span class="identifier">f1</span><span class="special">()</span></code>.
 379     </p>
 380 <p>
 381       </p>
 382 <h5>
 383 <a name="ecv2_destructor%20destructor_bridgehead"></a>
 384   <span><a name="ecv2_destructor%20destructor"></a></span>
 385   <a class="link" href="ecv2.html#ecv2_destructor%20destructor">Destructor</a>
 386 </h5>
 387 <p>
 388     </p>
 389 <pre class="programlisting"><span class="special">~</span><span class="identifier">execution_context</span><span class="special">();</span>
 390 </pre>
 391 <div class="variablelist">
 392 <p class="title"><b></b></p>
 393 <dl>
 394 <dt><span class="term">Effects:</span></dt>
 395 <dd><p>
 396             Destructs the associated stack if <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is a valid context, e.g. <span class="emphasis"><em>execution_context::operator
 397             bool()</em></span> returns <code class="computeroutput"><span class="keyword">true</span></code>.
 398           </p></dd>
 399 <dt><span class="term">Throws:</span></dt>
 400 <dd><p>
 401             Nothing.
 402           </p></dd>
 403 </dl>
 404 </div>
 405 <p>
 406       </p>
 407 <h5>
 408 <a name="ecv2_move%20constructor_bridgehead"></a>
 409   <span><a name="ecv2_move%20constructor"></a></span>
 410   <a class="link" href="ecv2.html#ecv2_move%20constructor">Move
 411       constructor</a>
 412 </h5>
 413 <p>
 414     </p>
 415 <pre class="programlisting"><span class="identifier">execution_context</span><span class="special">(</span> <span class="identifier">execution_context</span> <span class="special">&amp;&amp;</span> <span class="identifier">other</span><span class="special">)</span> <span class="keyword">noexcept</span><span class="special">;</span>
 416 </pre>
 417 <div class="variablelist">
 418 <p class="title"><b></b></p>
 419 <dl>
 420 <dt><span class="term">Effects:</span></dt>
 421 <dd><p>
 422             Moves underlying capture record to <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>.
 423           </p></dd>
 424 <dt><span class="term">Throws:</span></dt>
 425 <dd><p>
 426             Nothing.
 427           </p></dd>
 428 </dl>
 429 </div>
 430 <p>
 431       </p>
 432 <h5>
 433 <a name="ecv2_move%20assignment_bridgehead"></a>
 434   <span><a name="ecv2_move%20assignment"></a></span>
 435   <a class="link" href="ecv2.html#ecv2_move%20assignment">Move
 436       assignment operator</a>
 437 </h5>
 438 <p>
 439     </p>
 440 <pre class="programlisting"><span class="identifier">execution_context</span> <span class="special">&amp;</span> <span class="keyword">operator</span><span class="special">=(</span> <span class="identifier">execution_context</span> <span class="special">&amp;&amp;</span> <span class="identifier">other</span><span class="special">)</span> <span class="keyword">noexcept</span><span class="special">;</span>
 441 </pre>
 442 <div class="variablelist">
 443 <p class="title"><b></b></p>
 444 <dl>
 445 <dt><span class="term">Effects:</span></dt>
 446 <dd><p>
 447             Moves the state of <code class="computeroutput"><span class="identifier">other</span></code>
 448             to <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>
 449             using move semantics.
 450           </p></dd>
 451 <dt><span class="term">Throws:</span></dt>
 452 <dd><p>
 453             Nothing.
 454           </p></dd>
 455 </dl>
 456 </div>
 457 <p>
 458       </p>
 459 <h5>
 460 <a name="ecv2_operator_bool_bridgehead"></a>
 461   <span><a name="ecv2_operator_bool"></a></span>
 462   <a class="link" href="ecv2.html#ecv2_operator_bool">Member function
 463       <code class="computeroutput">operator bool</code>()</a>
 464 </h5>
 465 <p>
 466     </p>
 467 <pre class="programlisting"><span class="keyword">explicit</span> <span class="keyword">operator</span> <span class="keyword">bool</span><span class="special">()</span> <span class="keyword">const</span> <span class="keyword">noexcept</span><span class="special">;</span>
 468 </pre>
 469 <div class="variablelist">
 470 <p class="title"><b></b></p>
 471 <dl>
 472 <dt><span class="term">Returns:</span></dt>
 473 <dd><p>
 474             <code class="computeroutput"><span class="keyword">true</span></code> if <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> points to a capture record.
 475           </p></dd>
 476 <dt><span class="term">Throws:</span></dt>
 477 <dd><p>
 478             Nothing.
 479           </p></dd>
 480 </dl>
 481 </div>
 482 <p>
 483       </p>
 484 <h5>
 485 <a name="ecv2_operator_not_bridgehead"></a>
 486   <span><a name="ecv2_operator_not"></a></span>
 487   <a class="link" href="ecv2.html#ecv2_operator_not">Member function
 488       <code class="computeroutput">operator!</code>()</a>
 489 </h5>
 490 <p>
 491     </p>
 492 <pre class="programlisting"><span class="keyword">bool</span> <span class="keyword">operator</span><span class="special">!()</span> <span class="keyword">const</span> <span class="keyword">noexcept</span><span class="special">;</span>
 493 </pre>
 494 <div class="variablelist">
 495 <p class="title"><b></b></p>
 496 <dl>
 497 <dt><span class="term">Returns:</span></dt>
 498 <dd><p>
 499             <code class="computeroutput"><span class="keyword">true</span></code> if <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> does not point to a capture record.
 500           </p></dd>
 501 <dt><span class="term">Throws:</span></dt>
 502 <dd><p>
 503             Nothing.
 504           </p></dd>
 505 </dl>
 506 </div>
 507 <p>
 508       </p>
 509 <h5>
 510 <a name="ecv2_operator_call_bridgehead"></a>
 511   <span><a name="ecv2_operator_call"></a></span>
 512   <a class="link" href="ecv2.html#ecv2_operator_call">Member function
 513       <code class="computeroutput">operator()</code>()</a>
 514 </h5>
 515 <p>
 516     </p>
 517 <pre class="programlisting"><span class="identifier">std</span><span class="special">::</span><span class="identifier">tuple</span><span class="special">&lt;</span> <span class="identifier">execution_context</span><span class="special">&lt;</span> <span class="identifier">Args</span> <span class="special">...</span> <span class="special">&gt;,</span> <span class="identifier">Args</span> <span class="special">...</span> <span class="special">&gt;</span> <span class="keyword">operator</span><span class="special">()(</span> <span class="identifier">Args</span> <span class="special">...</span> <span class="identifier">args</span><span class="special">);</span> <span class="comment">// member of generic execution_context template</span>
 518
 519 <span class="identifier">execution_context</span><span class="special">&lt;</span> <span class="keyword">void</span> <span class="special">&gt;</span> <span class="keyword">operator</span><span class="special">()();</span> <span class="comment">// member of execution_context&lt; void &gt;</span>
 520 </pre>
 521 <div class="variablelist">
 522 <p class="title"><b></b></p>
 523 <dl>
 524 <dt><span class="term">Effects:</span></dt>
 525 <dd><p>
 526             Stores internally the current context data (stack pointer, instruction
 527             pointer, and CPU registers) of the current active context and restores
 528             the context data from <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>, which implies jumping to <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>'s
 529             context. The arguments, <code class="computeroutput"><span class="special">...</span> <span class="identifier">args</span></code>, are passed to the current context
 530             to be returned by the most recent call to <code class="computeroutput"><span class="identifier">execution_context</span><span class="special">::</span><span class="keyword">operator</span><span class="special">()</span></code> in the same thread.
 531           </p></dd>
 532 <dt><span class="term">Returns:</span></dt>
 533 <dd><p>
 534             The tuple of execution_context and returned arguments passed to the most
 535             recent call to <code class="computeroutput"><span class="identifier">execution_context</span><span class="special">::</span><span class="keyword">operator</span><span class="special">()</span></code>, if any and a execution_context representing
 536             the context that has been suspended.
 537           </p></dd>
 538 <dt><span class="term">Note:</span></dt>
 539 <dd><p>
 540             The returned execution_context indicates if the suspended context has
 541             terminated (return from context-function) via <code class="computeroutput"><span class="keyword">bool</span>
 542             <span class="keyword">operator</span><span class="special">()</span></code>.
 543             If the returned execution_context has terminated no data are transferred
 544             in the returned tuple.
 545           </p></dd>
 546 </dl>
 547 </div>
 548 <p>
 549       </p>
 550 <h5>
 551 <a name="ecv2_operator_call_ontop_bridgehead"></a>
 552   <span><a name="ecv2_operator_call_ontop"></a></span>
 553   <a class="link" href="ecv2.html#ecv2_operator_call_ontop">Member
 554       function <code class="computeroutput">operator()</code>()</a>
 555 </h5>
 556 <p>
 557     </p>
 558 <pre class="programlisting"><span class="keyword">template</span><span class="special">&lt;</span> <span class="keyword">typename</span> <span class="identifier">Fn</span> <span class="special">&gt;</span>
 559 <span class="identifier">std</span><span class="special">::</span><span class="identifier">tuple</span><span class="special">&lt;</span> <span class="identifier">execution_context</span><span class="special">&lt;</span> <span class="identifier">Args</span> <span class="special">...</span> <span class="special">&gt;,</span> <span class="identifier">Args</span> <span class="special">...</span> <span class="special">&gt;</span> <span class="keyword">operator</span><span class="special">()(</span> <span class="identifier">exec_ontop_arg_t</span><span class="special">,</span> <span class="identifier">Fn</span> <span class="special">&amp;&amp;</span> <span class="identifier">fn</span><span class="special">,</span> <span class="identifier">Args</span> <span class="special">...</span> <span class="identifier">args</span><span class="special">);</span> <span class="comment">// member of generic execution_context</span>
 560
 561 <span class="keyword">template</span><span class="special">&lt;</span> <span class="keyword">typename</span> <span class="identifier">Fn</span> <span class="special">&gt;</span>
 562 <span class="identifier">execution_context</span><span class="special">&lt;</span> <span class="keyword">void</span> <span class="special">&gt;</span> <span class="keyword">operator</span><span class="special">()(</span> <span class="identifier">exec_ontop_arg_t</span><span class="special">,</span> <span class="identifier">Fn</span> <span class="special">&amp;&amp;</span> <span class="identifier">fn</span><span class="special">);</span> <span class="comment">// member of execution_context&lt; void &gt;</span>
 563 </pre>
 564 <div class="variablelist">
 565 <p class="title"><b></b></p>
 566 <dl>
 567 <dt><span class="term">Effects:</span></dt>
 568 <dd><p>
 569             Same as <span class="emphasis"><em>execution_context::operator()</em></span>. Additionally,
 570             function <code class="computeroutput"><span class="identifier">fn</span></code> is executed
 571             in the context of <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>
 572             (e.g. the stack frame of <code class="computeroutput"><span class="identifier">fn</span></code>
 573             is allocated on stack of <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>).
 574           </p></dd>
 575 <dt><span class="term">Returns:</span></dt>
 576 <dd><p>
 577             The tuple of execution_context and returned arguments passed to the most
 578             recent call to <code class="computeroutput"><span class="identifier">execution_context</span><span class="special">::</span><span class="keyword">operator</span><span class="special">()</span></code>, if any and a execution_context representing
 579             the context that has been suspended .
 580           </p></dd>
 581 <dt><span class="term">Note:</span></dt>
 582 <dd><p>
 583             The tuple of execution_context and returned arguments from <code class="computeroutput"><span class="identifier">fn</span></code> are passed as arguments to the context-function
 584             of resumed context (if the context is entered the first time) or those
 585             arguments are returned from <code class="computeroutput"><span class="identifier">execution_context</span><span class="special">::</span><span class="keyword">operator</span><span class="special">()</span></code> within the resumed context.
 586           </p></dd>
 587 <dt><span class="term">Note:</span></dt>
 588 <dd><p>
 589             Function <code class="computeroutput"><span class="identifier">fn</span></code> needs to
 590             return a tuple of arguments (<a class="link" href="ecv2.html#ecv2_ontop">see description</a>).
 591           </p></dd>
 592 <dt><span class="term">Note:</span></dt>
 593 <dd><p>
 594             The context calling this function must not be destroyed before the arguments,
 595             that will be returned from <code class="computeroutput"><span class="identifier">fn</span></code>,
 596             are preserved at least in the stack frame of the resumed context.
 597           </p></dd>
 598 <dt><span class="term">Note:</span></dt>
 599 <dd><p>
 600             The returned execution_context indicates if the suspended context has
 601             terminated (return from context-function) via <code class="computeroutput"><span class="keyword">bool</span>
 602             <span class="keyword">operator</span><span class="special">()</span></code>.
 603             If the returned execution_context has terminated no data are transferred
 604             in the returned tuple.
 605           </p></dd>
 606 </dl>
 607 </div>
 608 <p>
 609       </p>
 610 <h5>
 611 <a name="ecv2_operator_equal_bridgehead"></a>
 612   <span><a name="ecv2_operator_equal"></a></span>
 613   <a class="link" href="ecv2.html#ecv2_operator_equal">Member
 614       function <code class="computeroutput">operator==</code>()</a>
 615 </h5>
 616 <p>
 617     </p>
 618 <pre class="programlisting"><span class="keyword">bool</span> <span class="keyword">operator</span><span class="special">==(</span> <span class="identifier">execution_context</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">other</span><span class="special">)</span> <span class="keyword">const</span> <span class="keyword">noexcept</span><span class="special">;</span>
 619 </pre>
 620 <div class="variablelist">
 621 <p class="title"><b></b></p>
 622 <dl>
 623 <dt><span class="term">Returns:</span></dt>
 624 <dd><p>
 625             <code class="computeroutput"><span class="keyword">true</span></code> if <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> and <code class="computeroutput"><span class="identifier">other</span></code>
 626             represent the same execution context, <code class="computeroutput"><span class="keyword">false</span></code>
 627             otherwise.
 628           </p></dd>
 629 <dt><span class="term">Throws:</span></dt>
 630 <dd><p>
 631             Nothing.
 632           </p></dd>
 633 </dl>
 634 </div>
 635 <p>
 636       </p>
 637 <h5>
 638 <a name="ecv2_operator_notequal_bridgehead"></a>
 639   <span><a name="ecv2_operator_notequal"></a></span>
 640   <a class="link" href="ecv2.html#ecv2_operator_notequal">Member
 641       function <code class="computeroutput">operator!=</code>()</a>
 642 </h5>
 643 <p>
 644     </p>
 645 <pre class="programlisting"><span class="keyword">bool</span> <span class="keyword">operator</span><span class="special">!=(</span> <span class="identifier">execution_context</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">other</span><span class="special">)</span> <span class="keyword">const</span> <span class="keyword">noexcept</span><span class="special">;</span>
 646 </pre>
 647 <div class="variablelist">
 648 <p class="title"><b></b></p>
 649 <dl>
 650 <dt><span class="term">Returns:</span></dt>
 651 <dd><p>
 652             <code class="computeroutput">! (other == * this)</code>
 653           </p></dd>
 654 <dt><span class="term">Throws:</span></dt>
 655 <dd><p>
 656             Nothing.
 657           </p></dd>
 658 </dl>
 659 </div>
 660 <p>
 661       </p>
 662 <h5>
 663 <a name="ecv2_operator_less_bridgehead"></a>
 664   <span><a name="ecv2_operator_less"></a></span>
 665   <a class="link" href="ecv2.html#ecv2_operator_less">Member function
 666       <code class="computeroutput">operator&lt;</code>()</a>
 667 </h5>
 668 <p>
 669     </p>
 670 <pre class="programlisting"><span class="keyword">bool</span> <span class="keyword">operator</span><span class="special">&lt;(</span> <span class="identifier">execution_context</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">other</span><span class="special">)</span> <span class="keyword">const</span> <span class="keyword">noexcept</span><span class="special">;</span>
 671 </pre>
 672 <div class="variablelist">
 673 <p class="title"><b></b></p>
 674 <dl>
 675 <dt><span class="term">Returns:</span></dt>
 676 <dd><p>
 677             <code class="computeroutput"><span class="keyword">true</span></code> if <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span> <span class="special">!=</span> <span class="identifier">other</span></code> is true and the implementation-defined
 678             total order of <code class="computeroutput"><span class="identifier">execution_context</span></code>
 679             values places <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>
 680             before <code class="computeroutput"><span class="identifier">other</span></code>, false otherwise.
 681           </p></dd>
 682 <dt><span class="term">Throws:</span></dt>
 683 <dd><p>
 684             Nothing.
 685           </p></dd>
 686 </dl>
 687 </div>
 688 <p>
 689       </p>
 690 <h5>
 691 <a name="ecv2_operator_greater_bridgehead"></a>
 692   <span><a name="ecv2_operator_greater"></a></span>
 693   <a class="link" href="ecv2.html#ecv2_operator_greater">Member
 694       function <code class="computeroutput">operator&gt;</code>()</a>
 695 </h5>
 696 <p>
 697     </p>
 698 <pre class="programlisting"><span class="keyword">bool</span> <span class="keyword">operator</span><span class="special">&gt;(</span> <span class="identifier">execution_context</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">other</span><span class="special">)</span> <span class="keyword">const</span> <span class="keyword">noexcept</span><span class="special">;</span>
 699 </pre>
 700 <div class="variablelist">
 701 <p class="title"><b></b></p>
 702 <dl>
 703 <dt><span class="term">Returns:</span></dt>
 704 <dd><p>
 705             <code class="computeroutput"><span class="identifier">other</span> <span class="special">&lt;</span>
 706             <span class="special">*</span> <span class="keyword">this</span></code>
 707           </p></dd>
 708 <dt><span class="term">Throws:</span></dt>
 709 <dd><p>
 710             Nothing.
 711           </p></dd>
 712 </dl>
 713 </div>
 714 <p>
 715       </p>
 716 <h5>
 717 <a name="ecv2_operator_lesseq_bridgehead"></a>
 718   <span><a name="ecv2_operator_lesseq"></a></span>
 719   <a class="link" href="ecv2.html#ecv2_operator_lesseq">Member
 720       function <code class="computeroutput">operator&lt;=</code>()</a>
 721 </h5>
 722 <p>
 723     </p>
 724 <pre class="programlisting"><span class="keyword">bool</span> <span class="keyword">operator</span><span class="special">&lt;=(</span> <span class="identifier">execution_context</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">other</span><span class="special">)</span> <span class="keyword">const</span> <span class="keyword">noexcept</span><span class="special">;</span>
 725 </pre>
 726 <div class="variablelist">
 727 <p class="title"><b></b></p>
 728 <dl>
 729 <dt><span class="term">Returns:</span></dt>
 730 <dd><p>
 731             <code class="computeroutput"><span class="special">!</span> <span class="special">(</span><span class="identifier">other</span> <span class="special">&lt;</span>
 732             <span class="special">*</span> <span class="keyword">this</span><span class="special">)</span></code>
 733           </p></dd>
 734 <dt><span class="term">Throws:</span></dt>
 735 <dd><p>
 736             Nothing.
 737           </p></dd>
 738 </dl>
 739 </div>
 740 <p>
 741       </p>
 742 <h5>
 743 <a name="ecv2_operator_greatereq_bridgehead"></a>
 744   <span><a name="ecv2_operator_greatereq"></a></span>
 745   <a class="link" href="ecv2.html#ecv2_operator_greatereq">Member
 746       function <code class="computeroutput">operator&gt;=</code>()</a>
 747 </h5>
 748 <p>
 749     </p>
 750 <pre class="programlisting"><span class="keyword">bool</span> <span class="keyword">operator</span><span class="special">&gt;=(</span> <span class="identifier">execution_context</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">other</span><span class="special">)</span> <span class="keyword">const</span> <span class="keyword">noexcept</span><span class="special">;</span>
 751 </pre>
 752 <div class="variablelist">
 753 <p class="title"><b></b></p>
 754 <dl>
 755 <dt><span class="term">Returns:</span></dt>
 756 <dd><p>
 757             <code class="computeroutput"><span class="special">!</span> <span class="special">(*</span>
 758             <span class="keyword">this</span> <span class="special">&lt;</span>
 759             <span class="identifier">other</span><span class="special">)</span></code>
 760           </p></dd>
 761 <dt><span class="term">Throws:</span></dt>
 762 <dd><p>
 763             Nothing.
 764           </p></dd>
 765 </dl>
 766 </div>
 767 <p>
 768       </p>
 769 <h5>
 770 <a name="ecv2__bridgehead"></a>
 771   <span><a name="ecv2_"></a></span>
 772   <a class="link" href="ecv2.html#ecv2_">Non-member function <code class="computeroutput">operator&lt;&lt;()</code></a>
 773 </h5>
 774 <p>
 775     </p>
 776 <pre class="programlisting"><span class="keyword">template</span><span class="special">&lt;</span> <span class="keyword">typename</span> <span class="identifier">charT</span><span class="special">,</span> <span class="keyword">class</span> <span class="identifier">traitsT</span> <span class="special">&gt;</span>
 777 <span class="identifier">std</span><span class="special">::</span><span class="identifier">basic_ostream</span><span class="special">&lt;</span> <span class="identifier">charT</span><span class="special">,</span> <span class="identifier">traitsT</span> <span class="special">&gt;</span> <span class="special">&amp;</span>
 778 <span class="keyword">operator</span><span class="special">&lt;&lt;(</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">basic_ostream</span><span class="special">&lt;</span> <span class="identifier">charT</span><span class="special">,</span> <span class="identifier">traitsT</span> <span class="special">&gt;</span> <span class="special">&amp;</span> <span class="identifier">os</span><span class="special">,</span> <span class="identifier">execution_context</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">other</span><span class="special">);</span>
 779 </pre>
 780 <div class="variablelist">
 781 <p class="title"><b></b></p>
 782 <dl>
 783 <dt><span class="term">Efects:</span></dt>
 784 <dd><p>
 785             Writes the representation of <code class="computeroutput"><span class="identifier">other</span></code>
 786             to stream <code class="computeroutput"><span class="identifier">os</span></code>.
 787           </p></dd>
 788 <dt><span class="term">Returns:</span></dt>
 789 <dd><p>
 790             <code class="computeroutput"><span class="identifier">os</span></code>
 791           </p></dd>
 792 </dl>
 793 </div>
 794 </div>
 795 <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
 796 <td align="left"></td>
 797 <td align="right"><div class="copyright-footer">Copyright &#169; 2014 Oliver Kowalke<p>
 798         Distributed under the Boost Software License, Version 1.0. (See accompanying
 799         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>)
 800       </p>
 801 </div></td>
 802 </tr></table>
 803 <hr>
 804 <div class="spirit-nav">
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