1<html> 2<head> 3<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII"> 4<title>Class execution_context (version 2)</title> 5<link rel="stylesheet" href="../../../../../doc/src/boostbook.css" type="text/css"> 6<meta name="generator" content="DocBook XSL Stylesheets V1.75.2"> 7<link rel="home" href="../index.html" title="Chapter 1. Context"> 8<link rel="up" href="../index.html" title="Chapter 1. Context"> 9<link rel="prev" href="cc/class__continuation_.html" title="Class continuation"> 10<link rel="next" href="ecv1.html" title="Class execution_context (version 1)"> 11</head> 12<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> 13<table cellpadding="2" width="100%"><tr> 14<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../boost.png"></td> 15<td align="center"><a href="../../../../../index.html">Home</a></td> 16<td align="center"><a href="../../../../../libs/libraries.htm">Libraries</a></td> 17<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td> 18<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td> 19<td align="center"><a href="../../../../../more/index.htm">More</a></td> 20</tr></table> 21<hr> 22<div class="spirit-nav"> 23<a accesskey="p" href="cc/class__continuation_.html"><img src="../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../index.html"><img src="../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../index.html"><img src="../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="ecv1.html"><img src="../../../../../doc/src/images/next.png" alt="Next"></a> 24</div> 25<div class="section"> 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"><</span><span class="keyword">int</span><span class="special">></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"><</span><span class="keyword">int</span><span class="special">></span> <span class="special">&&</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">--></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"><</span><span class="number">0</span><span class="special">>(</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"><</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"><</span><span class="number">0</span><span class="special">>(</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"><<</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">get</span><span class="special"><</span><span class="number">1</span><span class="special">>(</span><span class="identifier">result</span><span class="special">)<<</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<></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"><</span><span class="keyword">void</span><span class="special">></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"><</span><span class="keyword">void</span><span class="special">></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"><</span><span class="keyword">void</span><span class="special">></span> <span class="special">&&</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"><</span><span class="keyword">int</span><span class="special">></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"><</span><span class="keyword">int</span><span class="special">></span> <span class="special">&&</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"><</span><span class="keyword">int</span><span class="special">,</span><span class="keyword">int</span><span class="special">></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"><</span><span class="keyword">int</span><span class="special">,</span><span class="keyword">int</span><span class="special">></span> <span class="special">&&</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<></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"><</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">variant</span><span class="special"><</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">>></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"><</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">variant</span><span class="special"><</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">>></span> <span class="special">&&</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"><</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">></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"><</span><span class="keyword">int</span><span class="special">>(</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"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">>(</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"><</span><span class="number">0</span><span class="special">>(</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"><</span><span class="number">1</span><span class="special">>(</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">&)</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"><</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">></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"><</span><span class="number">0</span><span class="special">>(</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"><</span><span class="number">1</span><span class="special">>(</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"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">>(</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"><<</span> <span class="identifier">x</span><span class="special">(</span><span class="number">7</span><span class="special">)</span> <span class="special"><<</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<></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"><</span><span class="keyword">int</span><span class="special">></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"><</span><span class="keyword">int</span><span class="special">></span> <span class="special">&&</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"><<</span> <span class="string">"f1: entered first time: "</span> <span class="special"><<</span> <span class="identifier">data</span> <span class="special"><<</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"><<</span> <span class="string">"f1: entered second time: "</span> <span class="special"><<</span> <span class="identifier">data</span> <span class="special"><<</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"><<</span> <span class="string">"f1: entered third time: "</span> <span class="special"><<</span> <span class="identifier">data</span> <span class="special"><<</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"><<</span> <span class="string">"f2: entered: "</span> <span class="special"><<</span> <span class="identifier">data</span> <span class="special"><<</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"><</span> <span class="keyword">int</span> <span class="special">></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"><<</span> <span class="string">"f1: returned first time: "</span> <span class="special"><<</span> <span class="identifier">data</span> <span class="special"><<</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"><<</span> <span class="string">"f1: returned second time: "</span> <span class="special"><<</span> <span class="identifier">data</span> <span class="special"><<</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">&&</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">&</span> <span class="keyword">operator</span><span class="special">=(</span> <span class="identifier">execution_context</span> <span class="special">&&</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"><</span> <span class="identifier">execution_context</span><span class="special"><</span> <span class="identifier">Args</span> <span class="special">...</span> <span class="special">>,</span> <span class="identifier">Args</span> <span class="special">...</span> <span class="special">></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"><</span> <span class="keyword">void</span> <span class="special">></span> <span class="keyword">operator</span><span class="special">()();</span> <span class="comment">// member of execution_context< void ></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"><</span> <span class="keyword">typename</span> <span class="identifier">Fn</span> <span class="special">></span> 559<span class="identifier">std</span><span class="special">::</span><span class="identifier">tuple</span><span class="special"><</span> <span class="identifier">execution_context</span><span class="special"><</span> <span class="identifier">Args</span> <span class="special">...</span> <span class="special">>,</span> <span class="identifier">Args</span> <span class="special">...</span> <span class="special">></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">&&</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"><</span> <span class="keyword">typename</span> <span class="identifier">Fn</span> <span class="special">></span> 562<span class="identifier">execution_context</span><span class="special"><</span> <span class="keyword">void</span> <span class="special">></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">&&</span> <span class="identifier">fn</span><span class="special">);</span> <span class="comment">// member of execution_context< void ></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">&</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">&</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<</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"><(</span> <span class="identifier">execution_context</span> <span class="keyword">const</span><span class="special">&</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></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">>(</span> <span class="identifier">execution_context</span> <span class="keyword">const</span><span class="special">&</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"><</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<=</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"><=(</span> <span class="identifier">execution_context</span> <span class="keyword">const</span><span class="special">&</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"><</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>=</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">>=(</span> <span class="identifier">execution_context</span> <span class="keyword">const</span><span class="special">&</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"><</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<<()</code></a> 773</h5> 774<p> 775 </p> 776<pre class="programlisting"><span class="keyword">template</span><span class="special"><</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">></span> 777<span class="identifier">std</span><span class="special">::</span><span class="identifier">basic_ostream</span><span class="special"><</span> <span class="identifier">charT</span><span class="special">,</span> <span class="identifier">traitsT</span> <span class="special">></span> <span class="special">&</span> 778<span class="keyword">operator</span><span class="special"><<(</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">basic_ostream</span><span class="special"><</span> <span class="identifier">charT</span><span class="special">,</span> <span class="identifier">traitsT</span> <span class="special">></span> <span class="special">&</span> <span class="identifier">os</span><span class="special">,</span> <span class="identifier">execution_context</span> <span class="keyword">const</span><span class="special">&</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 © 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"> 805<a accesskey="p" href="cc/class__continuation_.html"><img src="../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../index.html"><img src="../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../index.html"><img src="../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="ecv1.html"><img src="../../../../../doc/src/images/next.png" alt="Next"></a> 806</div> 807</body> 808</html> 809
