1<html> 2<head> 3<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 4<title>Template promise<></title> 5<link rel="stylesheet" href="../../../../../../../doc/src/boostbook.css" type="text/css"> 6<meta name="generator" content="DocBook XSL Stylesheets V1.79.1"> 7<link rel="home" href="../../../index.html" title="Chapter 1. Fiber"> 8<link rel="up" href="../futures.html" title="Futures"> 9<link rel="prev" href="future.html" title="Future"> 10<link rel="next" href="packaged_task.html" title="Template packaged_task<>"> 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="future.html"><img src="../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../futures.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="packaged_task.html"><img src="../../../../../../../doc/src/images/next.png" alt="Next"></a> 24</div> 25<div class="section"> 26<div class="titlepage"><div><div><h4 class="title"> 27<a name="fiber.synchronization.futures.promise"></a><a name="class_promise"></a><a class="link" href="promise.html" title="Template promise<>">Template 28 <code class="computeroutput"><span class="identifier">promise</span><span class="special"><></span></code></a> 29</h4></div></div></div> 30<p> 31 A <a class="link" href="promise.html#class_promise"><code class="computeroutput">promise<></code></a> provides a mechanism to store a value (or 32 exception) that can later be retrieved from the corresponding <a class="link" href="future.html#class_future"><code class="computeroutput">future<></code></a> object. 33 <code class="computeroutput"><span class="identifier">promise</span><span class="special"><></span></code> 34 and <code class="computeroutput"><span class="identifier">future</span><span class="special"><></span></code> 35 communicate via their underlying <a class="link" href="future.html#shared_state">shared state</a>. 36 </p> 37<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">fiber</span><span class="special">/</span><span class="identifier">future</span><span class="special">/</span><span class="identifier">promise</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 38 39<span class="keyword">namespace</span> <span class="identifier">boost</span> <span class="special">{</span> 40<span class="keyword">namespace</span> <span class="identifier">fibers</span> <span class="special">{</span> 41 42<span class="keyword">template</span><span class="special"><</span> <span class="keyword">typename</span> <span class="identifier">R</span> <span class="special">></span> 43<span class="keyword">class</span> <span class="identifier">promise</span> <span class="special">{</span> 44<span class="keyword">public</span><span class="special">:</span> 45 <span class="identifier">promise</span><span class="special">();</span> 46 47 <span class="keyword">template</span><span class="special"><</span> <span class="keyword">typename</span> <a href="http://en.cppreference.com/w/cpp/concept/Allocator" target="_top"><code class="computeroutput"><span class="identifier">Allocator</span></code></a> <span class="special">></span> 48 <span class="identifier">promise</span><span class="special">(</span> <a href="http://en.cppreference.com/w/cpp/memory/allocator_arg_t" target="_top"><code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">allocator_arg_t</span></code></a><span class="special">,</span> <span class="identifier">Allocator</span><span class="special">);</span> 49 50 <span class="identifier">promise</span><span class="special">(</span> <span class="identifier">promise</span> <span class="special">&&)</span> <span class="keyword">noexcept</span><span class="special">;</span> 51 52 <span class="identifier">promise</span> <span class="special">&</span> <span class="keyword">operator</span><span class="special">=(</span> <span class="identifier">promise</span> <span class="special">&&)</span> <span class="keyword">noexcept</span><span class="special">;</span> 53 54 <span class="identifier">promise</span><span class="special">(</span> <span class="identifier">promise</span> <span class="keyword">const</span><span class="special">&)</span> <span class="special">=</span> <span class="keyword">delete</span><span class="special">;</span> 55 56 <span class="identifier">promise</span> <span class="special">&</span> <span class="keyword">operator</span><span class="special">=(</span> <span class="identifier">promise</span> <span class="keyword">const</span><span class="special">&)</span> <span class="special">=</span> <span class="keyword">delete</span><span class="special">;</span> 57 58 <span class="special">~</span><span class="identifier">promise</span><span class="special">();</span> 59 60 <span class="keyword">void</span> <span class="identifier">swap</span><span class="special">(</span> <span class="identifier">promise</span> <span class="special">&)</span> <span class="keyword">noexcept</span><span class="special">;</span> 61 62 <span class="identifier">future</span><span class="special"><</span> <span class="identifier">R</span> <span class="special">></span> <span class="identifier">get_future</span><span class="special">();</span> 63 64 <span class="keyword">void</span> <span class="identifier">set_value</span><span class="special">(</span> <span class="identifier">R</span> <span class="keyword">const</span><span class="special">&);</span> <span class="comment">// member only of generic promise template</span> 65 <span class="keyword">void</span> <span class="identifier">set_value</span><span class="special">(</span> <span class="identifier">R</span> <span class="special">&&);</span> <span class="comment">// member only of generic promise template</span> 66 <span class="keyword">void</span> <span class="identifier">set_value</span><span class="special">(</span> <span class="identifier">R</span> <span class="special">&);</span> <span class="comment">// member only of promise< R & > template</span> 67 <span class="keyword">void</span> <span class="identifier">set_value</span><span class="special">();</span> <span class="comment">// member only of promise< void > template</span> 68 69 <span class="keyword">void</span> <span class="identifier">set_exception</span><span class="special">(</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">exception_ptr</span> <span class="identifier">p</span><span class="special">);</span> 70<span class="special">};</span> 71 72<span class="keyword">template</span><span class="special"><</span> <span class="keyword">typename</span> <span class="identifier">R</span> <span class="special">></span> 73<span class="keyword">void</span> <span class="identifier">swap</span><span class="special">(</span> <span class="identifier">promise</span><span class="special"><</span> <span class="identifier">R</span> <span class="special">></span> <span class="special">&,</span> <span class="identifier">promise</span><span class="special"><</span> <span class="identifier">R</span> <span class="special">></span> <span class="special">&)</span> <span class="keyword">noexcept</span><span class="special">;</span> 74 75<span class="special">}</span> 76</pre> 77<h6> 78<a name="fiber.synchronization.futures.promise.h0"></a> 79 <span class="phrase"><a name="fiber.synchronization.futures.promise.default_constructor"></a></span><a class="link" href="promise.html#fiber.synchronization.futures.promise.default_constructor">Default 80 constructor</a> 81 </h6> 82<pre class="programlisting"><span class="identifier">promise</span><span class="special">();</span> 83</pre> 84<div class="variablelist"> 85<p class="title"><b></b></p> 86<dl class="variablelist"> 87<dt><span class="term">Effects:</span></dt> 88<dd><p> 89 Creates a promise with an empty <a class="link" href="future.html#shared_state">shared 90 state</a>. 91 </p></dd> 92<dt><span class="term">Throws:</span></dt> 93<dd><p> 94 Exceptions caused by memory allocation. 95 </p></dd> 96</dl> 97</div> 98<h6> 99<a name="fiber.synchronization.futures.promise.h1"></a> 100 <span class="phrase"><a name="fiber.synchronization.futures.promise.constructor"></a></span><a class="link" href="promise.html#fiber.synchronization.futures.promise.constructor">Constructor</a> 101 </h6> 102<pre class="programlisting"><span class="keyword">template</span><span class="special"><</span> <span class="keyword">typename</span> <a href="http://en.cppreference.com/w/cpp/concept/Allocator" target="_top"><code class="computeroutput"><span class="identifier">Allocator</span></code></a> <span class="special">></span> 103<span class="identifier">promise</span><span class="special">(</span> <a href="http://en.cppreference.com/w/cpp/memory/allocator_arg_t" target="_top"><code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">allocator_arg_t</span></code></a><span class="special">,</span> <span class="identifier">Allocator</span> <span class="identifier">alloc</span><span class="special">);</span> 104</pre> 105<div class="variablelist"> 106<p class="title"><b></b></p> 107<dl class="variablelist"> 108<dt><span class="term">Effects:</span></dt> 109<dd><p> 110 Creates a promise with an empty <a class="link" href="future.html#shared_state">shared 111 state</a> by using <code class="computeroutput"><span class="identifier">alloc</span></code>. 112 </p></dd> 113<dt><span class="term">Throws:</span></dt> 114<dd><p> 115 Exceptions caused by memory allocation. 116 </p></dd> 117<dt><span class="term">See also:</span></dt> 118<dd><p> 119 <a href="http://en.cppreference.com/w/cpp/memory/allocator_arg_t" target="_top"><code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">allocator_arg_t</span></code></a> 120 </p></dd> 121</dl> 122</div> 123<h6> 124<a name="fiber.synchronization.futures.promise.h2"></a> 125 <span class="phrase"><a name="fiber.synchronization.futures.promise.move_constructor"></a></span><a class="link" href="promise.html#fiber.synchronization.futures.promise.move_constructor">Move constructor</a> 126 </h6> 127<pre class="programlisting"><span class="identifier">promise</span><span class="special">(</span> <span class="identifier">promise</span> <span class="special">&&</span> <span class="identifier">other</span><span class="special">)</span> <span class="keyword">noexcept</span><span class="special">;</span> 128</pre> 129<div class="variablelist"> 130<p class="title"><b></b></p> 131<dl class="variablelist"> 132<dt><span class="term">Effects:</span></dt> 133<dd><p> 134 Creates a promise by moving the <a class="link" href="future.html#shared_state">shared 135 state</a> from <code class="computeroutput"><span class="identifier">other</span></code>. 136 </p></dd> 137<dt><span class="term">Postcondition:</span></dt> 138<dd><p> 139 <code class="computeroutput"><span class="identifier">other</span></code> contains no 140 valid shared state. 141 </p></dd> 142<dt><span class="term">Throws:</span></dt> 143<dd><p> 144 Nothing. 145 </p></dd> 146</dl> 147</div> 148<h6> 149<a name="fiber.synchronization.futures.promise.h3"></a> 150 <span class="phrase"><a name="fiber.synchronization.futures.promise.destructor"></a></span><a class="link" href="promise.html#fiber.synchronization.futures.promise.destructor">Destructor</a> 151 </h6> 152<pre class="programlisting"><span class="special">~</span><span class="identifier">promise</span><span class="special">();</span> 153</pre> 154<div class="variablelist"> 155<p class="title"><b></b></p> 156<dl class="variablelist"> 157<dt><span class="term">Effects:</span></dt> 158<dd><p> 159 Destroys <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> 160 and abandons the <a class="link" href="future.html#shared_state">shared state</a> 161 if shared state is ready; otherwise stores <code class="computeroutput"><span class="identifier">future_error</span></code> 162 with error condition <code class="computeroutput"><span class="identifier">future_errc</span><span class="special">::</span><span class="identifier">broken_promise</span></code> 163 as if by <a class="link" href="promise.html#promise_set_exception"><code class="computeroutput">promise::set_exception()</code></a>: the shared 164 state is set ready. 165 </p></dd> 166</dl> 167</div> 168<p> 169 </p> 170<h5> 171<a name="promise_operator_assign_bridgehead"></a> 172 <span class="phrase"><a name="promise_operator_assign"></a></span> 173 <a class="link" href="promise.html#promise_operator_assign">Member 174 function <code class="computeroutput">operator=</code>()</a> 175</h5> 176<p> 177 </p> 178<pre class="programlisting"><span class="identifier">promise</span> <span class="special">&</span> <span class="keyword">operator</span><span class="special">=(</span> <span class="identifier">promise</span> <span class="special">&&</span> <span class="identifier">other</span><span class="special">)</span> <span class="keyword">noexcept</span><span class="special">;</span> 179</pre> 180<div class="variablelist"> 181<p class="title"><b></b></p> 182<dl class="variablelist"> 183<dt><span class="term">Effects:</span></dt> 184<dd><p> 185 Transfers the ownership of <a class="link" href="future.html#shared_state">shared state</a> 186 to <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>. 187 </p></dd> 188<dt><span class="term">Postcondition:</span></dt> 189<dd><p> 190 <code class="computeroutput"><span class="identifier">other</span></code> contains no 191 valid shared state. 192 </p></dd> 193<dt><span class="term">Throws:</span></dt> 194<dd><p> 195 Nothing. 196 </p></dd> 197</dl> 198</div> 199<p> 200 </p> 201<h5> 202<a name="promise_swap_bridgehead"></a> 203 <span class="phrase"><a name="promise_swap"></a></span> 204 <a class="link" href="promise.html#promise_swap">Member function <code class="computeroutput">swap</code>()</a> 205</h5> 206<p> 207 </p> 208<pre class="programlisting"><span class="keyword">void</span> <span class="identifier">swap</span><span class="special">(</span> <span class="identifier">promise</span> <span class="special">&</span> <span class="identifier">other</span><span class="special">)</span> <span class="keyword">noexcept</span><span class="special">;</span> 209</pre> 210<div class="variablelist"> 211<p class="title"><b></b></p> 212<dl class="variablelist"> 213<dt><span class="term">Effects:</span></dt> 214<dd><p> 215 Swaps the <a class="link" href="future.html#shared_state">shared state</a> between 216 other and <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>. 217 </p></dd> 218<dt><span class="term">Throws:</span></dt> 219<dd><p> 220 Nothing. 221 </p></dd> 222</dl> 223</div> 224<p> 225 </p> 226<h5> 227<a name="promise_get_future_bridgehead"></a> 228 <span class="phrase"><a name="promise_get_future"></a></span> 229 <a class="link" href="promise.html#promise_get_future">Member 230 function <code class="computeroutput">get_future</code>()</a> 231</h5> 232<p> 233 </p> 234<pre class="programlisting"><span class="identifier">future</span><span class="special"><</span> <span class="identifier">R</span> <span class="special">></span> <span class="identifier">get_future</span><span class="special">();</span> 235</pre> 236<div class="variablelist"> 237<p class="title"><b></b></p> 238<dl class="variablelist"> 239<dt><span class="term">Returns:</span></dt> 240<dd><p> 241 A <a class="link" href="future.html#class_future"><code class="computeroutput">future<></code></a> with the same <a class="link" href="future.html#shared_state">shared 242 state</a>. 243 </p></dd> 244<dt><span class="term">Throws:</span></dt> 245<dd><p> 246 <code class="computeroutput"><span class="identifier">future_error</span></code> with 247 <code class="computeroutput"><span class="identifier">future_errc</span><span class="special">::</span><span class="identifier">future_already_retrieved</span></code> or <code class="computeroutput"><span class="identifier">future_errc</span><span class="special">::</span><span class="identifier">no_state</span></code>. 248 </p></dd> 249</dl> 250</div> 251<p> 252 </p> 253<h5> 254<a name="promise_set_value_bridgehead"></a> 255 <span class="phrase"><a name="promise_set_value"></a></span> 256 <a class="link" href="promise.html#promise_set_value">Member function 257 <code class="computeroutput">set_value</code>()</a> 258</h5> 259<p> 260 </p> 261<pre class="programlisting"><span class="keyword">void</span> <span class="identifier">set_value</span><span class="special">(</span> <span class="identifier">R</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">value</span><span class="special">);</span> <span class="comment">// member only of generic promise template</span> 262<span class="keyword">void</span> <span class="identifier">set_value</span><span class="special">(</span> <span class="identifier">R</span> <span class="special">&&</span> <span class="identifier">value</span><span class="special">);</span> <span class="comment">// member only of generic promise template</span> 263<span class="keyword">void</span> <span class="identifier">set_value</span><span class="special">(</span> <span class="identifier">R</span> <span class="special">&</span> <span class="identifier">value</span><span class="special">);</span> <span class="comment">// member only of promise< R & > template</span> 264<span class="keyword">void</span> <span class="identifier">set_value</span><span class="special">();</span> <span class="comment">// member only of promise< void > template</span> 265</pre> 266<div class="variablelist"> 267<p class="title"><b></b></p> 268<dl class="variablelist"> 269<dt><span class="term">Effects:</span></dt> 270<dd><p> 271 Store the result in the <a class="link" href="future.html#shared_state">shared state</a> 272 and marks the state as ready. 273 </p></dd> 274<dt><span class="term">Throws:</span></dt> 275<dd><p> 276 <code class="computeroutput"><span class="identifier">future_error</span></code> with 277 <code class="computeroutput"><span class="identifier">future_errc</span><span class="special">::</span><span class="identifier">future_already_satisfied</span></code> or <code class="computeroutput"><span class="identifier">future_errc</span><span class="special">::</span><span class="identifier">no_state</span></code>. 278 </p></dd> 279</dl> 280</div> 281<p> 282 </p> 283<h5> 284<a name="promise_set_exception_bridgehead"></a> 285 <span class="phrase"><a name="promise_set_exception"></a></span> 286 <a class="link" href="promise.html#promise_set_exception">Member 287 function <code class="computeroutput">set_exception</code>()</a> 288</h5> 289<p> 290 </p> 291<pre class="programlisting"><span class="keyword">void</span> <span class="identifier">set_exception</span><span class="special">(</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">exception_ptr</span><span class="special">);</span> 292</pre> 293<div class="variablelist"> 294<p class="title"><b></b></p> 295<dl class="variablelist"> 296<dt><span class="term">Effects:</span></dt> 297<dd><p> 298 Store an exception pointer in the <a class="link" href="future.html#shared_state">shared 299 state</a> and marks the state as ready. 300 </p></dd> 301<dt><span class="term">Throws:</span></dt> 302<dd><p> 303 <code class="computeroutput"><span class="identifier">future_error</span></code> with 304 <code class="computeroutput"><span class="identifier">future_errc</span><span class="special">::</span><span class="identifier">future_already_satisfied</span></code> or <code class="computeroutput"><span class="identifier">future_errc</span><span class="special">::</span><span class="identifier">no_state</span></code>. 305 </p></dd> 306</dl> 307</div> 308<p> 309 </p> 310<h5> 311<a name="swap_for_promise_bridgehead"></a> 312 <span class="phrase"><a name="swap_for_promise"></a></span> 313 <a class="link" href="promise.html#swap_for_promise">Non-member function 314 <code class="computeroutput">swap()</code></a> 315</h5> 316<p> 317 </p> 318<pre class="programlisting"><span class="keyword">template</span><span class="special"><</span> <span class="keyword">typename</span> <span class="identifier">R</span> <span class="special">></span> 319<span class="keyword">void</span> <span class="identifier">swap</span><span class="special">(</span> <span class="identifier">promise</span><span class="special"><</span> <span class="identifier">R</span> <span class="special">></span> <span class="special">&</span> <span class="identifier">l</span><span class="special">,</span> <span class="identifier">promise</span><span class="special"><</span> <span class="identifier">R</span> <span class="special">></span> <span class="special">&</span> <span class="identifier">r</span><span class="special">)</span> <span class="keyword">noexcept</span><span class="special">;</span> 320</pre> 321<div class="variablelist"> 322<p class="title"><b></b></p> 323<dl class="variablelist"> 324<dt><span class="term">Effects:</span></dt> 325<dd><p> 326 Same as <code class="computeroutput"><span class="identifier">l</span><span class="special">.</span><span class="identifier">swap</span><span class="special">(</span> 327 <span class="identifier">r</span><span class="special">)</span></code>. 328 </p></dd> 329</dl> 330</div> 331</div> 332<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 333<td align="left"></td> 334<td align="right"><div class="copyright-footer">Copyright © 2013 Oliver Kowalke<p> 335 Distributed under the Boost Software License, Version 1.0. (See accompanying 336 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>) 337 </p> 338</div></td> 339</tr></table> 340<hr> 341<div class="spirit-nav"> 342<a accesskey="p" href="future.html"><img src="../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../futures.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="packaged_task.html"><img src="../../../../../../../doc/src/images/next.png" alt="Next"></a> 343</div> 344</body> 345</html> 346
