1<html> 2<head> 3<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 4<title>Condition Variables</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="../synchronization.html" title="Synchronization"> 9<link rel="prev" href="mutex_types.html" title="Mutex Types"> 10<link rel="next" href="barriers.html" title="Barriers"> 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="mutex_types.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../synchronization.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="barriers.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a> 24</div> 25<div class="section"> 26<div class="titlepage"><div><div><h3 class="title"> 27<a name="fiber.synchronization.conditions"></a><a class="link" href="conditions.html" title="Condition Variables">Condition Variables</a> 28</h3></div></div></div> 29<h5> 30<a name="fiber.synchronization.conditions.h0"></a> 31 <span class="phrase"><a name="fiber.synchronization.conditions.synopsis"></a></span><a class="link" href="conditions.html#fiber.synchronization.conditions.synopsis">Synopsis</a> 32 </h5> 33<pre class="programlisting"><span class="keyword">enum</span> <span class="keyword">class</span> <span class="identifier">cv_status</span><span class="special">;</span> <span class="special">{</span> 34 <span class="identifier">no_timeout</span><span class="special">,</span> 35 <span class="identifier">timeout</span> 36<span class="special">};</span> 37 38<span class="keyword">class</span> <span class="identifier">condition_variable</span><span class="special">;</span> 39<span class="keyword">class</span> <span class="identifier">condition_variable_any</span><span class="special">;</span> 40</pre> 41<p> 42 The class <a class="link" href="conditions.html#class_condition_variable"><code class="computeroutput">condition_variable</code></a> provides a mechanism 43 for a fiber to wait for notification from another fiber. When the fiber awakens 44 from the wait, then it checks to see if the appropriate condition is now 45 true, and continues if so. If the condition is not true, then the fiber calls 46 <code class="computeroutput"><span class="identifier">wait</span></code> again to resume waiting. 47 In the simplest case, this condition is just a boolean variable: 48 </p> 49<pre class="programlisting"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">fibers</span><span class="special">::</span><span class="identifier">condition_variable</span> <span class="identifier">cond</span><span class="special">;</span> 50<span class="identifier">boost</span><span class="special">::</span><span class="identifier">fibers</span><span class="special">::</span><span class="identifier">mutex</span> <span class="identifier">mtx</span><span class="special">;</span> 51<span class="keyword">bool</span> <span class="identifier">data_ready</span> <span class="special">=</span> <span class="keyword">false</span><span class="special">;</span> 52 53<span class="keyword">void</span> <span class="identifier">process_data</span><span class="special">();</span> 54 55<span class="keyword">void</span> <span class="identifier">wait_for_data_to_process</span><span class="special">()</span> <span class="special">{</span> 56 <span class="special">{</span> 57 <span class="identifier">std</span><span class="special">::</span><span class="identifier">unique_lock</span><span class="special"><</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">fibers</span><span class="special">::</span><span class="identifier">mutex</span> <span class="special">></span> <span class="identifier">lk</span><span class="special">(</span> <span class="identifier">mtx</span><span class="special">);</span> 58 <span class="keyword">while</span> <span class="special">(</span> <span class="special">!</span> <span class="identifier">data_ready</span><span class="special">)</span> <span class="special">{</span> 59 <span class="identifier">cond</span><span class="special">.</span><span class="identifier">wait</span><span class="special">(</span> <span class="identifier">lk</span><span class="special">);</span> 60 <span class="special">}</span> 61 <span class="special">}</span> <span class="comment">// release lk</span> 62 <span class="identifier">process_data</span><span class="special">();</span> 63<span class="special">}</span> 64</pre> 65<p> 66 Notice that the <code class="computeroutput"><span class="identifier">lk</span></code> is passed 67 to <a class="link" href="conditions.html#condition_variable_wait"><code class="computeroutput">condition_variable::wait()</code></a>: <code class="computeroutput"><span class="identifier">wait</span><span class="special">()</span></code> will atomically add the fiber to the set 68 of fibers waiting on the condition variable, and unlock the <a class="link" href="mutex_types.html#class_mutex"><code class="computeroutput">mutex</code></a>. 69 When the fiber is awakened, the <code class="computeroutput"><span class="identifier">mutex</span></code> 70 will be locked again before the call to <code class="computeroutput"><span class="identifier">wait</span><span class="special">()</span></code> returns. This allows other fibers to acquire 71 the <code class="computeroutput"><span class="identifier">mutex</span></code> in order to update 72 the shared data, and ensures that the data associated with the condition 73 is correctly synchronized. 74 </p> 75<p> 76 <code class="computeroutput"><span class="identifier">wait_for_data_to_process</span><span class="special">()</span></code> could equivalently be written: 77 </p> 78<pre class="programlisting"><span class="keyword">void</span> <span class="identifier">wait_for_data_to_process</span><span class="special">()</span> <span class="special">{</span> 79 <span class="special">{</span> 80 <span class="identifier">std</span><span class="special">::</span><span class="identifier">unique_lock</span><span class="special"><</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">fibers</span><span class="special">::</span><span class="identifier">mutex</span> <span class="special">></span> <span class="identifier">lk</span><span class="special">(</span> <span class="identifier">mtx</span><span class="special">);</span> 81 <span class="comment">// make condition_variable::wait() perform the loop</span> 82 <span class="identifier">cond</span><span class="special">.</span><span class="identifier">wait</span><span class="special">(</span> <span class="identifier">lk</span><span class="special">,</span> <span class="special">[](){</span> <span class="keyword">return</span> <span class="identifier">data_ready</span><span class="special">;</span> <span class="special">});</span> 83 <span class="special">}</span> <span class="comment">// release lk</span> 84 <span class="identifier">process_data</span><span class="special">();</span> 85<span class="special">}</span> 86</pre> 87<p> 88 In the meantime, another fiber sets <code class="computeroutput"><span class="identifier">data_ready</span></code> 89 to <code class="computeroutput"><span class="keyword">true</span></code>, and then calls either 90 <a class="link" href="conditions.html#condition_variable_notify_one"><code class="computeroutput">condition_variable::notify_one()</code></a> or <a class="link" href="conditions.html#condition_variable_notify_all"><code class="computeroutput">condition_variable::notify_all()</code></a> on 91 the <a class="link" href="conditions.html#class_condition_variable"><code class="computeroutput">condition_variable</code></a> <code class="computeroutput"><span class="identifier">cond</span></code> 92 to wake one waiting fiber or all the waiting fibers respectively. 93 </p> 94<pre class="programlisting"><span class="keyword">void</span> <span class="identifier">retrieve_data</span><span class="special">();</span> 95<span class="keyword">void</span> <span class="identifier">prepare_data</span><span class="special">();</span> 96 97<span class="keyword">void</span> <span class="identifier">prepare_data_for_processing</span><span class="special">()</span> <span class="special">{</span> 98 <span class="identifier">retrieve_data</span><span class="special">();</span> 99 <span class="identifier">prepare_data</span><span class="special">();</span> 100 <span class="special">{</span> 101 <span class="identifier">std</span><span class="special">::</span><span class="identifier">unique_lock</span><span class="special"><</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">fibers</span><span class="special">::</span><span class="identifier">mutex</span> <span class="special">></span> <span class="identifier">lk</span><span class="special">(</span> <span class="identifier">mtx</span><span class="special">);</span> 102 <span class="identifier">data_ready</span> <span class="special">=</span> <span class="keyword">true</span><span class="special">;</span> 103 <span class="special">}</span> 104 <span class="identifier">cond</span><span class="special">.</span><span class="identifier">notify_one</span><span class="special">();</span> 105<span class="special">}</span> 106</pre> 107<p> 108 Note that the same <a class="link" href="mutex_types.html#class_mutex"><code class="computeroutput">mutex</code></a> is locked before the shared data is updated, 109 but that the <code class="computeroutput"><span class="identifier">mutex</span></code> does not 110 have to be locked across the call to <a class="link" href="conditions.html#condition_variable_notify_one"><code class="computeroutput">condition_variable::notify_one()</code></a>. 111 </p> 112<p> 113 Locking is important because the synchronization objects provided by <span class="bold"><strong>Boost.Fiber</strong></span> can be used to synchronize fibers running 114 on different threads. 115 </p> 116<p> 117 <span class="bold"><strong>Boost.Fiber</strong></span> provides both <a class="link" href="conditions.html#class_condition_variable"><code class="computeroutput">condition_variable</code></a> and 118 <a class="link" href="conditions.html#class_condition_variable_any"><code class="computeroutput">condition_variable_any</code></a>. <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">fibers</span><span class="special">::</span><span class="identifier">condition_variable</span></code> 119 can only wait on <a href="http://en.cppreference.com/w/cpp/thread/unique_lock" target="_top"><code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">unique_lock</span></code></a><code class="computeroutput"><span class="special"><</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">fibers</span><span class="special">::</span></code><a class="link" href="mutex_types.html#class_mutex"><code class="computeroutput">mutex</code></a><code class="computeroutput"> <span class="special">></span></code> 120 while <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">fibers</span><span class="special">::</span><span class="identifier">condition_variable_any</span></code> can wait on user-defined 121 lock types. 122 </p> 123<a name="condition_variable_spurious_wakeups"></a><h5> 124<a name="fiber.synchronization.conditions.h1"></a> 125 <span class="phrase"><a name="fiber.synchronization.conditions.no_spurious_wakeups"></a></span><a class="link" href="conditions.html#fiber.synchronization.conditions.no_spurious_wakeups">No Spurious 126 Wakeups</a> 127 </h5> 128<p> 129 Neither <a class="link" href="conditions.html#class_condition_variable"><code class="computeroutput">condition_variable</code></a> nor <a class="link" href="conditions.html#class_condition_variable_any"><code class="computeroutput">condition_variable_any</code></a> are 130 subject to spurious wakeup: <a class="link" href="conditions.html#condition_variable_wait"><code class="computeroutput">condition_variable::wait()</code></a> can 131 only wake up when <a class="link" href="conditions.html#condition_variable_notify_one"><code class="computeroutput">condition_variable::notify_one()</code></a> or 132 <a class="link" href="conditions.html#condition_variable_notify_all"><code class="computeroutput">condition_variable::notify_all()</code></a> is called. Even 133 so, it is prudent to use one of the <code class="computeroutput"><span class="identifier">wait</span><span class="special">(</span> <span class="identifier">lock</span><span class="special">,</span> <span class="identifier">predicate</span> <span class="special">)</span></code> overloads. 134 </p> 135<p> 136 Consider a set of consumer fibers processing items from a <a href="http://en.cppreference.com/w/cpp/container/queue" target="_top"><code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">queue</span></code></a>. 137 The queue is continually populated by a set of producer fibers. 138 </p> 139<p> 140 The consumer fibers might reasonably wait on a <code class="computeroutput"><span class="identifier">condition_variable</span></code> 141 as long as the queue remains <a href="http://en.cppreference.com/w/cpp/container/queue/empty" target="_top"><code class="computeroutput"><span class="identifier">empty</span><span class="special">()</span></code></a>. 142 </p> 143<p> 144 Because producer fibers might <a href="http://en.cppreference.com/w/cpp/container/queue/push" target="_top"><code class="computeroutput"><span class="identifier">push</span><span class="special">()</span></code></a> 145 items to the queue in bursts, they call <a class="link" href="conditions.html#condition_variable_notify_all"><code class="computeroutput">condition_variable::notify_all()</code></a> rather 146 than <a class="link" href="conditions.html#condition_variable_notify_one"><code class="computeroutput">condition_variable::notify_one()</code></a>. 147 </p> 148<p> 149 But a given consumer fiber might well wake up from <a class="link" href="conditions.html#condition_variable_wait"><code class="computeroutput">condition_variable::wait()</code></a> and 150 find the queue <code class="computeroutput"><span class="identifier">empty</span><span class="special">()</span></code>, 151 because other consumer fibers might already have processed all pending items. 152 </p> 153<p> 154 (See also <a class="link" href="../rationale.html#spurious_wakeup">spurious wakeup</a>.) 155 </p> 156<a name="class_cv_status"></a><h5> 157<a name="fiber.synchronization.conditions.h2"></a> 158 <span class="phrase"><a name="fiber.synchronization.conditions.enumeration__code__phrase_role__identifier__cv_status__phrase___code_"></a></span><a class="link" href="conditions.html#fiber.synchronization.conditions.enumeration__code__phrase_role__identifier__cv_status__phrase___code_">Enumeration 159 <code class="computeroutput"><span class="identifier">cv_status</span></code></a> 160 </h5> 161<p> 162 A timed wait operation might return because of timeout or not. 163 </p> 164<pre class="programlisting"><span class="keyword">enum</span> <span class="keyword">class</span> <span class="identifier">cv_status</span> <span class="special">{</span> 165 <span class="identifier">no_timeout</span><span class="special">,</span> 166 <span class="identifier">timeout</span> 167<span class="special">};</span> 168</pre> 169<h5> 170<a name="fiber.synchronization.conditions.h3"></a> 171 <span class="phrase"><a name="fiber.synchronization.conditions._code__phrase_role__identifier__no_timeout__phrase___code_"></a></span><a class="link" href="conditions.html#fiber.synchronization.conditions._code__phrase_role__identifier__no_timeout__phrase___code_"><code class="computeroutput"><span class="identifier">no_timeout</span></code></a> 172 </h5> 173<div class="variablelist"> 174<p class="title"><b></b></p> 175<dl class="variablelist"> 176<dt><span class="term">Effects:</span></dt> 177<dd><p> 178 The condition variable was awakened with <code class="computeroutput"><span class="identifier">notify_one</span></code> 179 or <code class="computeroutput"><span class="identifier">notify_all</span></code>. 180 </p></dd> 181</dl> 182</div> 183<h5> 184<a name="fiber.synchronization.conditions.h4"></a> 185 <span class="phrase"><a name="fiber.synchronization.conditions._code__phrase_role__identifier__timeout__phrase___code_"></a></span><a class="link" href="conditions.html#fiber.synchronization.conditions._code__phrase_role__identifier__timeout__phrase___code_"><code class="computeroutput"><span class="identifier">timeout</span></code></a> 186 </h5> 187<div class="variablelist"> 188<p class="title"><b></b></p> 189<dl class="variablelist"> 190<dt><span class="term">Effects:</span></dt> 191<dd><p> 192 The condition variable was awakened by timeout. 193 </p></dd> 194</dl> 195</div> 196<p> 197 </p> 198<h5> 199<a name="class_condition_variable_any_bridgehead"></a> 200 <span class="phrase"><a name="class_condition_variable_any"></a></span> 201 <a class="link" href="conditions.html#class_condition_variable_any">Class 202 <code class="computeroutput">condition_variable_any</code></a> 203</h5> 204<p> 205 </p> 206<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">condition_variable</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 207 208<span class="keyword">namespace</span> <span class="identifier">boost</span> <span class="special">{</span> 209<span class="keyword">namespace</span> <span class="identifier">fibers</span> <span class="special">{</span> 210 211<span class="keyword">class</span> condition_variable_any <span class="special">{</span> 212<span class="keyword">public</span><span class="special">:</span> 213 condition_variable_any<span class="special">();</span> 214 <span class="special">~</span>condition_variable_any<span class="special">();</span> 215 216 condition_variable_any<span class="special">(</span> condition_variable_any <span class="keyword">const</span><span class="special">&)</span> <span class="special">=</span> <span class="keyword">delete</span><span class="special">;</span> 217 condition_variable_any <span class="special">&</span> <span class="keyword">operator</span><span class="special">=(</span> condition_variable_any <span class="keyword">const</span><span class="special">&)</span> <span class="special">=</span> <span class="keyword">delete</span><span class="special">;</span> 218 219 <span class="keyword">void</span> <span class="identifier">notify_one</span><span class="special">()</span> <span class="keyword">noexcept</span><span class="special">;</span> 220 <span class="keyword">void</span> <span class="identifier">notify_all</span><span class="special">()</span> <span class="keyword">noexcept</span><span class="special">;</span> 221 222 template< typename LockType > 223 void <span class="identifier">wait</span><span class="special">(</span> LockType <span class="special">&);</span> 224 225 <span class="keyword">template</span><span class="special"><</span> typename LockType, typename <span class="identifier">Pred</span> <span class="special">></span> 226 <span class="keyword">void</span> <span class="identifier">wait</span><span class="special">(</span> LockType <span class="special">&,</span> <span class="identifier">Pred</span><span class="special">);</span> 227 228 <span class="keyword">template</span><span class="special"><</span> typename LockType, typename <span class="identifier">Clock</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">Duration</span> <span class="special">></span> 229 <span class="identifier">cv_status</span> <span class="identifier">wait_until</span><span class="special">(</span> LockType <span class="special">&,</span> 230 <span class="identifier">std</span><span class="special">::</span><span class="identifier">chrono</span><span class="special">::</span><span class="identifier">time_point</span><span class="special"><</span> <span class="identifier">Clock</span><span class="special">,</span> <span class="identifier">Duration</span> <span class="special">></span> <span class="keyword">const</span><span class="special">&);</span> 231 232 <span class="keyword">template</span><span class="special"><</span> typename LockType, typename <span class="identifier">Clock</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">Duration</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">Pred</span> <span class="special">></span> 233 <span class="keyword">bool</span> <span class="identifier">wait_until</span><span class="special">(</span> LockType <span class="special">&,</span> 234 <span class="identifier">std</span><span class="special">::</span><span class="identifier">chrono</span><span class="special">::</span><span class="identifier">time_point</span><span class="special"><</span> <span class="identifier">Clock</span><span class="special">,</span> <span class="identifier">Duration</span> <span class="special">></span> <span class="keyword">const</span><span class="special">&,</span> 235 <span class="identifier">Pred</span><span class="special">);</span> 236 237 <span class="keyword">template</span><span class="special"><</span> typename LockType, typename <span class="identifier">Rep</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">Period</span> <span class="special">></span> 238 <span class="identifier">cv_status</span> <span class="identifier">wait_for</span><span class="special">(</span> LockType <span class="special">&,</span> 239 <span class="identifier">std</span><span class="special">::</span><span class="identifier">chrono</span><span class="special">::</span><span class="identifier">duration</span><span class="special"><</span> <span class="identifier">Rep</span><span class="special">,</span> <span class="identifier">Period</span> <span class="special">></span> <span class="keyword">const</span><span class="special">&);</span> 240 241 <span class="keyword">template</span><span class="special"><</span> typename LockType, typename <span class="identifier">Rep</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">Period</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">Pred</span> <span class="special">></span> 242 <span class="keyword">bool</span> <span class="identifier">wait_for</span><span class="special">(</span> LockType <span class="special">&,</span> 243 <span class="identifier">std</span><span class="special">::</span><span class="identifier">chrono</span><span class="special">::</span><span class="identifier">duration</span><span class="special"><</span> <span class="identifier">Rep</span><span class="special">,</span> <span class="identifier">Period</span> <span class="special">></span> <span class="keyword">const</span><span class="special">&,</span> 244 <span class="identifier">Pred</span><span class="special">);</span> 245<span class="special">};</span> 246 247<span class="special">}}</span> 248</pre> 249<h5> 250<a name="fiber.synchronization.conditions.h5"></a> 251 <span class="phrase"><a name="fiber.synchronization.conditions.constructor"></a></span><a class="link" href="conditions.html#fiber.synchronization.conditions.constructor">Constructor</a> 252 </h5> 253<pre class="programlisting">condition_variable_any<span class="special">()</span> 254</pre> 255<div class="variablelist"> 256<p class="title"><b></b></p> 257<dl class="variablelist"> 258<dt><span class="term">Effects:</span></dt> 259<dd><p> 260 Creates the object. 261 </p></dd> 262<dt><span class="term">Throws:</span></dt> 263<dd><p> 264 Nothing. 265 </p></dd> 266</dl> 267</div> 268<h5> 269<a name="fiber.synchronization.conditions.h6"></a> 270 <span class="phrase"><a name="fiber.synchronization.conditions.destructor"></a></span><a class="link" href="conditions.html#fiber.synchronization.conditions.destructor">Destructor</a> 271 </h5> 272<pre class="programlisting"><span class="special">~</span>condition_variable_any<span class="special">()</span> 273</pre> 274<div class="variablelist"> 275<p class="title"><b></b></p> 276<dl class="variablelist"> 277<dt><span class="term">Precondition:</span></dt> 278<dd><p> 279 All fibers waiting on <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> have been notified by a call to 280 <code class="computeroutput"><span class="identifier">notify_one</span></code> or <code class="computeroutput"><span class="identifier">notify_all</span></code> (though the respective 281 calls to <code class="computeroutput"><span class="identifier">wait</span></code>, <code class="computeroutput"><span class="identifier">wait_for</span></code> or <code class="computeroutput"><span class="identifier">wait_until</span></code> 282 need not have returned). 283 </p></dd> 284<dt><span class="term">Effects:</span></dt> 285<dd><p> 286 Destroys the object. 287 </p></dd> 288</dl> 289</div> 290<p> 291 </p> 292<h5> 293<a name="condition_variable_any_notify_one_bridgehead"></a> 294 <span class="phrase"><a name="condition_variable_any_notify_one"></a></span> 295 <a class="link" href="conditions.html#condition_variable_any_notify_one">Member 296 function <code class="computeroutput">notify_one</code>()</a> 297</h5> 298<p> 299 </p> 300<pre class="programlisting"><span class="keyword">void</span> <span class="identifier">notify_one</span><span class="special">()</span> <span class="keyword">noexcept</span><span class="special">;</span> 301</pre> 302<div class="variablelist"> 303<p class="title"><b></b></p> 304<dl class="variablelist"> 305<dt><span class="term">Effects:</span></dt> 306<dd><p> 307 If any fibers are currently <a class="link" href="../overview.html#blocking"><span class="emphasis"><em>blocked</em></span></a> 308 waiting on <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> 309 in a call to <code class="computeroutput"><span class="identifier">wait</span></code>, 310 <code class="computeroutput"><span class="identifier">wait_for</span></code> or <code class="computeroutput"><span class="identifier">wait_until</span></code>, unblocks one of those 311 fibers. 312 </p></dd> 313<dt><span class="term">Throws:</span></dt> 314<dd><p> 315 Nothing. 316 </p></dd> 317<dt><span class="term">Note:</span></dt> 318<dd><p> 319 It is arbitrary which waiting fiber is resumed. 320 </p></dd> 321</dl> 322</div> 323<p> 324 </p> 325<h5> 326<a name="condition_variable_any_notify_all_bridgehead"></a> 327 <span class="phrase"><a name="condition_variable_any_notify_all"></a></span> 328 <a class="link" href="conditions.html#condition_variable_any_notify_all">Member 329 function <code class="computeroutput">notify_all</code>()</a> 330</h5> 331<p> 332 </p> 333<pre class="programlisting"><span class="keyword">void</span> <span class="identifier">notify_all</span><span class="special">()</span> <span class="keyword">noexcept</span><span class="special">;</span> 334</pre> 335<div class="variablelist"> 336<p class="title"><b></b></p> 337<dl class="variablelist"> 338<dt><span class="term">Effects:</span></dt> 339<dd><p> 340 If any fibers are currently <a class="link" href="../overview.html#blocking"><span class="emphasis"><em>blocked</em></span></a> 341 waiting on <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> 342 in a call to <code class="computeroutput"><span class="identifier">wait</span></code>, 343 <code class="computeroutput"><span class="identifier">wait_for</span></code> or <code class="computeroutput"><span class="identifier">wait_until</span></code>, unblocks all of those 344 fibers. 345 </p></dd> 346<dt><span class="term">Throws:</span></dt> 347<dd><p> 348 Nothing. 349 </p></dd> 350<dt><span class="term">Note:</span></dt> 351<dd><p> 352 This is why a waiting fiber must <span class="emphasis"><em>also</em></span> check for 353 the desired program state using a mechanism external to the <code class="computeroutput">condition_variable_any</code>, 354 and retry the wait until that state is reached. A fiber waiting on 355 a <code class="computeroutput">condition_variable_any</code> might well wake up a number of times before 356 the desired state is reached. 357 </p></dd> 358</dl> 359</div> 360<p> 361 </p> 362<h5> 363<a name="condition_variable_any_wait_bridgehead"></a> 364 <span class="phrase"><a name="condition_variable_any_wait"></a></span> 365 <a class="link" href="conditions.html#condition_variable_any_wait">Templated 366 member function <code class="computeroutput">wait</code>()</a> 367</h5> 368<p> 369 </p> 370<pre class="programlisting">template< typename LockType > 371 void <span class="identifier">wait</span><span class="special">(</span> LockType <span class="special">&</span> <span class="identifier">lk</span><span class="special">);</span> 372 373<span class="keyword">template</span><span class="special"><</span> typename LockType, typename <span class="identifier">Pred</span> <span class="special">></span> 374<span class="keyword">void</span> <span class="identifier">wait</span><span class="special">(</span> LockType <span class="special">&</span> <span class="identifier">lk</span><span class="special">,</span> <span class="identifier">Pred</span> <span class="identifier">pred</span><span class="special">);</span> 375</pre> 376<div class="variablelist"> 377<p class="title"><b></b></p> 378<dl class="variablelist"> 379<dt><span class="term">Precondition:</span></dt> 380<dd><p> 381 <code class="computeroutput"><span class="identifier">lk</span></code> is locked by the 382 current fiber, and either no other fiber is currently waiting on <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>, 383 or the execution of the <a href="http://en.cppreference.com/w/cpp/thread/unique_lock/mutex" target="_top"><code class="computeroutput"><span class="identifier">mutex</span><span class="special">()</span></code></a> 384 member function on the <code class="computeroutput"><span class="identifier">lk</span></code> 385 objects supplied in the calls to <code class="computeroutput"><span class="identifier">wait</span></code> 386 in all the fibers currently waiting on <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> would return the same value as 387 <code class="computeroutput"><span class="identifier">lk</span><span class="special">-></span><span class="identifier">mutex</span><span class="special">()</span></code> 388 for this call to <code class="computeroutput"><span class="identifier">wait</span></code>. 389 </p></dd> 390<dt><span class="term">Effects:</span></dt> 391<dd> 392<p> 393 Atomically call <code class="computeroutput"><span class="identifier">lk</span><span class="special">.</span><span class="identifier">unlock</span><span class="special">()</span></code> and blocks the current fiber. The 394 fiber will unblock when notified by a call to <code class="computeroutput"><span class="keyword">this</span><span class="special">-></span><span class="identifier">notify_one</span><span class="special">()</span></code> or <code class="computeroutput"><span class="keyword">this</span><span class="special">-></span><span class="identifier">notify_all</span><span class="special">()</span></code>. When the fiber is unblocked (for 395 whatever reason), the lock is reacquired by invoking <code class="computeroutput"><span class="identifier">lk</span><span class="special">.</span><span class="identifier">lock</span><span class="special">()</span></code> 396 before the call to <code class="computeroutput"><span class="identifier">wait</span></code> 397 returns. The lock is also reacquired by invoking <code class="computeroutput"><span class="identifier">lk</span><span class="special">.</span><span class="identifier">lock</span><span class="special">()</span></code> if the function exits with an exception. 398 The member function accepting <code class="computeroutput"><span class="identifier">pred</span></code> 399 is shorthand for: 400</p> 401<pre class="programlisting"><span class="keyword">while</span> <span class="special">(</span> <span class="special">!</span> <span class="identifier">pred</span><span class="special">()</span> <span class="special">)</span> <span class="special">{</span> 402 <span class="identifier">wait</span><span class="special">(</span> <span class="identifier">lk</span><span class="special">);</span> 403<span class="special">}</span> 404</pre> 405<p> 406 </p> 407</dd> 408<dt><span class="term">Postcondition:</span></dt> 409<dd><p> 410 <code class="computeroutput"><span class="identifier">lk</span></code> is locked by the 411 current fiber. 412 </p></dd> 413<dt><span class="term">Throws:</span></dt> 414<dd><p> 415 <code class="computeroutput"><span class="identifier">fiber_error</span></code> if an error 416 occurs. 417 </p></dd> 418<dt><span class="term">Note:</span></dt> 419<dd><p> 420 The Precondition is a bit dense. It merely states that all the fibers 421 concurrently calling <code class="computeroutput"><span class="identifier">wait</span></code> 422 on <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> 423 must wait on <code class="computeroutput"><span class="identifier">lk</span></code> objects 424 governing the <span class="emphasis"><em>same</em></span> <a class="link" href="mutex_types.html#class_mutex"><code class="computeroutput">mutex</code></a>. Three distinct 425 objects are involved in any <code class="computeroutput">condition_variable_any::wait()</code> call: the 426 <code class="computeroutput">condition_variable_any</code> itself, the <code class="computeroutput"><span class="identifier">mutex</span></code> 427 coordinating access between fibers and a local lock object (e.g. <a href="http://en.cppreference.com/w/cpp/thread/unique_lock" target="_top"><code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">unique_lock</span></code></a>). In general, 428 you can partition the lifespan of a given <code class="computeroutput">condition_variable_any</code> instance 429 into periods with one or more fibers waiting on it, separated by periods 430 when no fibers are waiting on it. When more than one fiber is waiting 431 on that <code class="computeroutput">condition_variable_any</code>, all must pass lock objects referencing 432 the <span class="emphasis"><em>same</em></span> <code class="computeroutput"><span class="identifier">mutex</span></code> 433 instance. 434 </p></dd> 435</dl> 436</div> 437<p> 438 </p> 439<h5> 440<a name="condition_variable_any_wait_until_bridgehead"></a> 441 <span class="phrase"><a name="condition_variable_any_wait_until"></a></span> 442 <a class="link" href="conditions.html#condition_variable_any_wait_until">Templated 443 member function <code class="computeroutput">wait_until</code>()</a> 444</h5> 445<p> 446 </p> 447<pre class="programlisting"><span class="keyword">template</span><span class="special"><</span> typename LockType, typename <span class="identifier">Clock</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">Duration</span> <span class="special">></span> 448<span class="identifier">cv_status</span> <span class="identifier">wait_until</span><span class="special">(</span> LockType <span class="special">&</span> <span class="identifier">lk</span><span class="special">,</span> 449 <span class="identifier">std</span><span class="special">::</span><span class="identifier">chrono</span><span class="special">::</span><span class="identifier">time_point</span><span class="special"><</span> <span class="identifier">Clock</span><span class="special">,</span> <span class="identifier">Duration</span> <span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">abs_time</span><span class="special">);</span> 450 451<span class="keyword">template</span><span class="special"><</span> typename LockType, typename <span class="identifier">Clock</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">Duration</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">Pred</span> <span class="special">></span> 452<span class="keyword">bool</span> <span class="identifier">wait_until</span><span class="special">(</span> LockType <span class="special">&</span> <span class="identifier">lk</span><span class="special">,</span> 453 <span class="identifier">std</span><span class="special">::</span><span class="identifier">chrono</span><span class="special">::</span><span class="identifier">time_point</span><span class="special"><</span> <span class="identifier">Clock</span><span class="special">,</span> <span class="identifier">Duration</span> <span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">abs_time</span><span class="special">,</span> 454 <span class="identifier">Pred</span> <span class="identifier">pred</span><span class="special">);</span> 455</pre> 456<div class="variablelist"> 457<p class="title"><b></b></p> 458<dl class="variablelist"> 459<dt><span class="term">Precondition:</span></dt> 460<dd><p> 461 <code class="computeroutput"><span class="identifier">lk</span></code> is locked by the 462 current fiber, and either no other fiber is currently waiting on <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>, 463 or the execution of the <code class="computeroutput"><span class="identifier">mutex</span><span class="special">()</span></code> member function on the <code class="computeroutput"><span class="identifier">lk</span></code> objects supplied in the calls 464 to <code class="computeroutput"><span class="identifier">wait</span></code>, <code class="computeroutput"><span class="identifier">wait_for</span></code> or <code class="computeroutput"><span class="identifier">wait_until</span></code> 465 in all the fibers currently waiting on <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> would return the same value as 466 <code class="computeroutput"><span class="identifier">lk</span><span class="special">.</span><span class="identifier">mutex</span><span class="special">()</span></code> 467 for this call to <code class="computeroutput"><span class="identifier">wait_until</span></code>. 468 </p></dd> 469<dt><span class="term">Effects:</span></dt> 470<dd> 471<p> 472 Atomically call <code class="computeroutput"><span class="identifier">lk</span><span class="special">.</span><span class="identifier">unlock</span><span class="special">()</span></code> and blocks the current fiber. The 473 fiber will unblock when notified by a call to <code class="computeroutput"><span class="keyword">this</span><span class="special">-></span><span class="identifier">notify_one</span><span class="special">()</span></code> or <code class="computeroutput"><span class="keyword">this</span><span class="special">-></span><span class="identifier">notify_all</span><span class="special">()</span></code>, when the system time would be equal 474 to or later than the specified <code class="computeroutput"><span class="identifier">abs_time</span></code>. 475 When the fiber is unblocked (for whatever reason), the lock is reacquired 476 by invoking <code class="computeroutput"><span class="identifier">lk</span><span class="special">.</span><span class="identifier">lock</span><span class="special">()</span></code> 477 before the call to <code class="computeroutput"><span class="identifier">wait_until</span></code> 478 returns. The lock is also reacquired by invoking <code class="computeroutput"><span class="identifier">lk</span><span class="special">.</span><span class="identifier">lock</span><span class="special">()</span></code> if the function exits with an exception. 479 The member function accepting <code class="computeroutput"><span class="identifier">pred</span></code> 480 is shorthand for: 481</p> 482<pre class="programlisting"><span class="keyword">while</span> <span class="special">(</span> <span class="special">!</span> <span class="identifier">pred</span><span class="special">()</span> <span class="special">)</span> <span class="special">{</span> 483 <span class="keyword">if</span> <span class="special">(</span> <span class="identifier">cv_status</span><span class="special">::</span><span class="identifier">timeout</span> <span class="special">==</span> <span class="identifier">wait_until</span><span class="special">(</span> <span class="identifier">lk</span><span class="special">,</span> <span class="identifier">abs_time</span><span class="special">)</span> <span class="special">)</span> 484 <span class="keyword">return</span> <span class="identifier">pred</span><span class="special">();</span> 485<span class="special">}</span> 486<span class="keyword">return</span> <span class="keyword">true</span><span class="special">;</span> 487</pre> 488<p> 489 That is, even if <code class="computeroutput"><span class="identifier">wait_until</span><span class="special">()</span></code> times out, it can still return <code class="computeroutput"><span class="keyword">true</span></code> if <code class="computeroutput"><span class="identifier">pred</span><span class="special">()</span></code> returns <code class="computeroutput"><span class="keyword">true</span></code> 490 at that time. 491 </p> 492</dd> 493<dt><span class="term">Postcondition:</span></dt> 494<dd><p> 495 <code class="computeroutput"><span class="identifier">lk</span></code> is locked by the 496 current fiber. 497 </p></dd> 498<dt><span class="term">Throws:</span></dt> 499<dd><p> 500 <code class="computeroutput"><span class="identifier">fiber_error</span></code> if an error 501 occurs or timeout-related exceptions. 502 </p></dd> 503<dt><span class="term">Returns:</span></dt> 504<dd><p> 505 The overload without <code class="computeroutput"><span class="identifier">pred</span></code> 506 returns <code class="computeroutput"><span class="identifier">cv_status</span><span class="special">::</span><span class="identifier">no_timeout</span></code> if awakened by <code class="computeroutput"><span class="identifier">notify_one</span><span class="special">()</span></code> 507 or <code class="computeroutput"><span class="identifier">notify_all</span><span class="special">()</span></code>, 508 or <code class="computeroutput"><span class="identifier">cv_status</span><span class="special">::</span><span class="identifier">timeout</span></code> if awakened because the system 509 time is past <code class="computeroutput"><span class="identifier">abs_time</span></code>. 510 </p></dd> 511<dt><span class="term">Returns:</span></dt> 512<dd><p> 513 The overload accepting <code class="computeroutput"><span class="identifier">pred</span></code> 514 returns <code class="computeroutput"><span class="keyword">false</span></code> if the call 515 is returning because the time specified by <code class="computeroutput"><span class="identifier">abs_time</span></code> 516 was reached and the predicate returns <code class="computeroutput"><span class="keyword">false</span></code>, 517 <code class="computeroutput"><span class="keyword">true</span></code> otherwise. 518 </p></dd> 519<dt><span class="term">Note:</span></dt> 520<dd><p> 521 See <span class="bold"><strong>Note</strong></span> for <a class="link" href="conditions.html#condition_variable_any_wait"><code class="computeroutput">condition_variable_any::wait()</code></a>. 522 </p></dd> 523</dl> 524</div> 525<p> 526 </p> 527<h5> 528<a name="condition_variable_any_wait_for_bridgehead"></a> 529 <span class="phrase"><a name="condition_variable_any_wait_for"></a></span> 530 <a class="link" href="conditions.html#condition_variable_any_wait_for">Templated 531 member function <code class="computeroutput">wait_for</code>()</a> 532</h5> 533<p> 534 </p> 535<pre class="programlisting"><span class="keyword">template</span><span class="special"><</span> typename LockType, typename <span class="identifier">Rep</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">Period</span> <span class="special">></span> 536<span class="identifier">cv_status</span> <span class="identifier">wait_for</span><span class="special">(</span> LockType <span class="special">&</span> <span class="identifier">lk</span><span class="special">,</span> 537 <span class="identifier">std</span><span class="special">::</span><span class="identifier">chrono</span><span class="special">::</span><span class="identifier">duration</span><span class="special"><</span> <span class="identifier">Rep</span><span class="special">,</span> <span class="identifier">Period</span> <span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">rel_time</span><span class="special">);</span> 538 539<span class="keyword">template</span><span class="special"><</span> typename LockType, typename <span class="identifier">Rep</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">Period</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">Pred</span> <span class="special">></span> 540<span class="keyword">bool</span> <span class="identifier">wait_for</span><span class="special">(</span> LockType <span class="special">&</span> <span class="identifier">lk</span><span class="special">,</span> 541 <span class="identifier">std</span><span class="special">::</span><span class="identifier">chrono</span><span class="special">::</span><span class="identifier">duration</span><span class="special"><</span> <span class="identifier">Rep</span><span class="special">,</span> <span class="identifier">Period</span> <span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">rel_time</span><span class="special">,</span> 542 <span class="identifier">Pred</span> <span class="identifier">pred</span><span class="special">);</span> 543</pre> 544<div class="variablelist"> 545<p class="title"><b></b></p> 546<dl class="variablelist"> 547<dt><span class="term">Precondition:</span></dt> 548<dd><p> 549 <code class="computeroutput"><span class="identifier">lk</span></code> is locked by the 550 current fiber, and either no other fiber is currently waiting on <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>, 551 or the execution of the <code class="computeroutput"><span class="identifier">mutex</span><span class="special">()</span></code> member function on the <code class="computeroutput"><span class="identifier">lk</span></code> objects supplied in the calls 552 to <code class="computeroutput"><span class="identifier">wait</span></code>, <code class="computeroutput"><span class="identifier">wait_for</span></code> or <code class="computeroutput"><span class="identifier">wait_until</span></code> 553 in all the fibers currently waiting on <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> would return the same value as 554 <code class="computeroutput"><span class="identifier">lk</span><span class="special">.</span><span class="identifier">mutex</span><span class="special">()</span></code> 555 for this call to <code class="computeroutput"><span class="identifier">wait_for</span></code>. 556 </p></dd> 557<dt><span class="term">Effects:</span></dt> 558<dd> 559<p> 560 Atomically call <code class="computeroutput"><span class="identifier">lk</span><span class="special">.</span><span class="identifier">unlock</span><span class="special">()</span></code> and blocks the current fiber. The 561 fiber will unblock when notified by a call to <code class="computeroutput"><span class="keyword">this</span><span class="special">-></span><span class="identifier">notify_one</span><span class="special">()</span></code> or <code class="computeroutput"><span class="keyword">this</span><span class="special">-></span><span class="identifier">notify_all</span><span class="special">()</span></code>, when a time interval equal to or 562 greater than the specified <code class="computeroutput"><span class="identifier">rel_time</span></code> 563 has elapsed. When the fiber is unblocked (for whatever reason), the 564 lock is reacquired by invoking <code class="computeroutput"><span class="identifier">lk</span><span class="special">.</span><span class="identifier">lock</span><span class="special">()</span></code> before the call to <code class="computeroutput"><span class="identifier">wait</span></code> returns. The lock is also reacquired 565 by invoking <code class="computeroutput"><span class="identifier">lk</span><span class="special">.</span><span class="identifier">lock</span><span class="special">()</span></code> 566 if the function exits with an exception. The <code class="computeroutput"><span class="identifier">wait_for</span><span class="special">()</span></code> member function accepting <code class="computeroutput"><span class="identifier">pred</span></code> is shorthand for: 567</p> 568<pre class="programlisting"><span class="keyword">while</span> <span class="special">(</span> <span class="special">!</span> <span class="identifier">pred</span><span class="special">()</span> <span class="special">)</span> <span class="special">{</span> 569 <span class="keyword">if</span> <span class="special">(</span> <span class="identifier">cv_status</span><span class="special">::</span><span class="identifier">timeout</span> <span class="special">==</span> <span class="identifier">wait_for</span><span class="special">(</span> <span class="identifier">lk</span><span class="special">,</span> <span class="identifier">rel_time</span><span class="special">)</span> <span class="special">)</span> <span class="special">{</span> 570 <span class="keyword">return</span> <span class="identifier">pred</span><span class="special">();</span> 571 <span class="special">}</span> 572<span class="special">}</span> 573<span class="keyword">return</span> <span class="keyword">true</span><span class="special">;</span> 574</pre> 575<p> 576 (except of course that <code class="computeroutput"><span class="identifier">rel_time</span></code> 577 is adjusted for each iteration). The point is that, even if <code class="computeroutput"><span class="identifier">wait_for</span><span class="special">()</span></code> 578 times out, it can still return <code class="computeroutput"><span class="keyword">true</span></code> 579 if <code class="computeroutput"><span class="identifier">pred</span><span class="special">()</span></code> 580 returns <code class="computeroutput"><span class="keyword">true</span></code> at that time. 581 </p> 582</dd> 583<dt><span class="term">Postcondition:</span></dt> 584<dd><p> 585 <code class="computeroutput"><span class="identifier">lk</span></code> is locked by the 586 current fiber. 587 </p></dd> 588<dt><span class="term">Throws:</span></dt> 589<dd><p> 590 <code class="computeroutput"><span class="identifier">fiber_error</span></code> if an error 591 occurs or timeout-related exceptions. 592 </p></dd> 593<dt><span class="term">Returns:</span></dt> 594<dd><p> 595 The overload without <code class="computeroutput"><span class="identifier">pred</span></code> 596 returns <code class="computeroutput"><span class="identifier">cv_status</span><span class="special">::</span><span class="identifier">no_timeout</span></code> if awakened by <code class="computeroutput"><span class="identifier">notify_one</span><span class="special">()</span></code> 597 or <code class="computeroutput"><span class="identifier">notify_all</span><span class="special">()</span></code>, 598 or <code class="computeroutput"><span class="identifier">cv_status</span><span class="special">::</span><span class="identifier">timeout</span></code> if awakened because at least 599 <code class="computeroutput"><span class="identifier">rel_time</span></code> has elapsed. 600 </p></dd> 601<dt><span class="term">Returns:</span></dt> 602<dd><p> 603 The overload accepting <code class="computeroutput"><span class="identifier">pred</span></code> 604 returns <code class="computeroutput"><span class="keyword">false</span></code> if the call 605 is returning because at least <code class="computeroutput"><span class="identifier">rel_time</span></code> 606 has elapsed and the predicate returns <code class="computeroutput"><span class="keyword">false</span></code>, 607 <code class="computeroutput"><span class="keyword">true</span></code> otherwise. 608 </p></dd> 609<dt><span class="term">Note:</span></dt> 610<dd><p> 611 See <span class="bold"><strong>Note</strong></span> for <a class="link" href="conditions.html#condition_variable_any_wait"><code class="computeroutput">condition_variable_any::wait()</code></a>. 612 </p></dd> 613</dl> 614</div> 615<p> 616 </p> 617<h5> 618<a name="class_condition_variable_bridgehead"></a> 619 <span class="phrase"><a name="class_condition_variable"></a></span> 620 <a class="link" href="conditions.html#class_condition_variable">Class 621 <code class="computeroutput">condition_variable</code></a> 622</h5> 623<p> 624 </p> 625<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">condition_variable</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 626 627<span class="keyword">namespace</span> <span class="identifier">boost</span> <span class="special">{</span> 628<span class="keyword">namespace</span> <span class="identifier">fibers</span> <span class="special">{</span> 629 630<span class="keyword">class</span> condition_variable <span class="special">{</span> 631<span class="keyword">public</span><span class="special">:</span> 632 condition_variable<span class="special">();</span> 633 <span class="special">~</span>condition_variable<span class="special">();</span> 634 635 condition_variable<span class="special">(</span> condition_variable <span class="keyword">const</span><span class="special">&)</span> <span class="special">=</span> <span class="keyword">delete</span><span class="special">;</span> 636 condition_variable <span class="special">&</span> <span class="keyword">operator</span><span class="special">=(</span> condition_variable <span class="keyword">const</span><span class="special">&)</span> <span class="special">=</span> <span class="keyword">delete</span><span class="special">;</span> 637 638 <span class="keyword">void</span> <span class="identifier">notify_one</span><span class="special">()</span> <span class="keyword">noexcept</span><span class="special">;</span> 639 <span class="keyword">void</span> <span class="identifier">notify_all</span><span class="special">()</span> <span class="keyword">noexcept</span><span class="special">;</span> 640 641 void <span class="identifier">wait</span><span class="special">(</span> std::unique_lock< mutex > <span class="special">&);</span> 642 643 <span class="keyword">template</span><span class="special"><</span> typename <span class="identifier">Pred</span> <span class="special">></span> 644 <span class="keyword">void</span> <span class="identifier">wait</span><span class="special">(</span> std::unique_lock< mutex > <span class="special">&,</span> <span class="identifier">Pred</span><span class="special">);</span> 645 646 <span class="keyword">template</span><span class="special"><</span> typename <span class="identifier">Clock</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">Duration</span> <span class="special">></span> 647 <span class="identifier">cv_status</span> <span class="identifier">wait_until</span><span class="special">(</span> std::unique_lock< mutex > <span class="special">&,</span> 648 <span class="identifier">std</span><span class="special">::</span><span class="identifier">chrono</span><span class="special">::</span><span class="identifier">time_point</span><span class="special"><</span> <span class="identifier">Clock</span><span class="special">,</span> <span class="identifier">Duration</span> <span class="special">></span> <span class="keyword">const</span><span class="special">&);</span> 649 650 <span class="keyword">template</span><span class="special"><</span> typename <span class="identifier">Clock</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">Duration</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">Pred</span> <span class="special">></span> 651 <span class="keyword">bool</span> <span class="identifier">wait_until</span><span class="special">(</span> std::unique_lock< mutex > <span class="special">&,</span> 652 <span class="identifier">std</span><span class="special">::</span><span class="identifier">chrono</span><span class="special">::</span><span class="identifier">time_point</span><span class="special"><</span> <span class="identifier">Clock</span><span class="special">,</span> <span class="identifier">Duration</span> <span class="special">></span> <span class="keyword">const</span><span class="special">&,</span> 653 <span class="identifier">Pred</span><span class="special">);</span> 654 655 <span class="keyword">template</span><span class="special"><</span> typename <span class="identifier">Rep</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">Period</span> <span class="special">></span> 656 <span class="identifier">cv_status</span> <span class="identifier">wait_for</span><span class="special">(</span> std::unique_lock< mutex > <span class="special">&,</span> 657 <span class="identifier">std</span><span class="special">::</span><span class="identifier">chrono</span><span class="special">::</span><span class="identifier">duration</span><span class="special"><</span> <span class="identifier">Rep</span><span class="special">,</span> <span class="identifier">Period</span> <span class="special">></span> <span class="keyword">const</span><span class="special">&);</span> 658 659 <span class="keyword">template</span><span class="special"><</span> typename <span class="identifier">Rep</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">Period</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">Pred</span> <span class="special">></span> 660 <span class="keyword">bool</span> <span class="identifier">wait_for</span><span class="special">(</span> std::unique_lock< mutex > <span class="special">&,</span> 661 <span class="identifier">std</span><span class="special">::</span><span class="identifier">chrono</span><span class="special">::</span><span class="identifier">duration</span><span class="special"><</span> <span class="identifier">Rep</span><span class="special">,</span> <span class="identifier">Period</span> <span class="special">></span> <span class="keyword">const</span><span class="special">&,</span> 662 <span class="identifier">Pred</span><span class="special">);</span> 663<span class="special">};</span> 664 665<span class="special">}}</span> 666</pre> 667<h5> 668<a name="fiber.synchronization.conditions.h7"></a> 669 <span class="phrase"><a name="fiber.synchronization.conditions.constructor0"></a></span><a class="link" href="conditions.html#fiber.synchronization.conditions.constructor0">Constructor</a> 670 </h5> 671<pre class="programlisting">condition_variable<span class="special">()</span> 672</pre> 673<div class="variablelist"> 674<p class="title"><b></b></p> 675<dl class="variablelist"> 676<dt><span class="term">Effects:</span></dt> 677<dd><p> 678 Creates the object. 679 </p></dd> 680<dt><span class="term">Throws:</span></dt> 681<dd><p> 682 Nothing. 683 </p></dd> 684</dl> 685</div> 686<h5> 687<a name="fiber.synchronization.conditions.h8"></a> 688 <span class="phrase"><a name="fiber.synchronization.conditions.destructor0"></a></span><a class="link" href="conditions.html#fiber.synchronization.conditions.destructor0">Destructor</a> 689 </h5> 690<pre class="programlisting"><span class="special">~</span>condition_variable<span class="special">()</span> 691</pre> 692<div class="variablelist"> 693<p class="title"><b></b></p> 694<dl class="variablelist"> 695<dt><span class="term">Precondition:</span></dt> 696<dd><p> 697 All fibers waiting on <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> have been notified by a call to 698 <code class="computeroutput"><span class="identifier">notify_one</span></code> or <code class="computeroutput"><span class="identifier">notify_all</span></code> (though the respective 699 calls to <code class="computeroutput"><span class="identifier">wait</span></code>, <code class="computeroutput"><span class="identifier">wait_for</span></code> or <code class="computeroutput"><span class="identifier">wait_until</span></code> 700 need not have returned). 701 </p></dd> 702<dt><span class="term">Effects:</span></dt> 703<dd><p> 704 Destroys the object. 705 </p></dd> 706</dl> 707</div> 708<p> 709 </p> 710<h5> 711<a name="condition_variable_notify_one_bridgehead"></a> 712 <span class="phrase"><a name="condition_variable_notify_one"></a></span> 713 <a class="link" href="conditions.html#condition_variable_notify_one">Member 714 function <code class="computeroutput">notify_one</code>()</a> 715</h5> 716<p> 717 </p> 718<pre class="programlisting"><span class="keyword">void</span> <span class="identifier">notify_one</span><span class="special">()</span> <span class="keyword">noexcept</span><span class="special">;</span> 719</pre> 720<div class="variablelist"> 721<p class="title"><b></b></p> 722<dl class="variablelist"> 723<dt><span class="term">Effects:</span></dt> 724<dd><p> 725 If any fibers are currently <a class="link" href="../overview.html#blocking"><span class="emphasis"><em>blocked</em></span></a> 726 waiting on <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> 727 in a call to <code class="computeroutput"><span class="identifier">wait</span></code>, 728 <code class="computeroutput"><span class="identifier">wait_for</span></code> or <code class="computeroutput"><span class="identifier">wait_until</span></code>, unblocks one of those 729 fibers. 730 </p></dd> 731<dt><span class="term">Throws:</span></dt> 732<dd><p> 733 Nothing. 734 </p></dd> 735<dt><span class="term">Note:</span></dt> 736<dd><p> 737 It is arbitrary which waiting fiber is resumed. 738 </p></dd> 739</dl> 740</div> 741<p> 742 </p> 743<h5> 744<a name="condition_variable_notify_all_bridgehead"></a> 745 <span class="phrase"><a name="condition_variable_notify_all"></a></span> 746 <a class="link" href="conditions.html#condition_variable_notify_all">Member 747 function <code class="computeroutput">notify_all</code>()</a> 748</h5> 749<p> 750 </p> 751<pre class="programlisting"><span class="keyword">void</span> <span class="identifier">notify_all</span><span class="special">()</span> <span class="keyword">noexcept</span><span class="special">;</span> 752</pre> 753<div class="variablelist"> 754<p class="title"><b></b></p> 755<dl class="variablelist"> 756<dt><span class="term">Effects:</span></dt> 757<dd><p> 758 If any fibers are currently <a class="link" href="../overview.html#blocking"><span class="emphasis"><em>blocked</em></span></a> 759 waiting on <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> 760 in a call to <code class="computeroutput"><span class="identifier">wait</span></code>, 761 <code class="computeroutput"><span class="identifier">wait_for</span></code> or <code class="computeroutput"><span class="identifier">wait_until</span></code>, unblocks all of those 762 fibers. 763 </p></dd> 764<dt><span class="term">Throws:</span></dt> 765<dd><p> 766 Nothing. 767 </p></dd> 768<dt><span class="term">Note:</span></dt> 769<dd><p> 770 This is why a waiting fiber must <span class="emphasis"><em>also</em></span> check for 771 the desired program state using a mechanism external to the <code class="computeroutput">condition_variable</code>, 772 and retry the wait until that state is reached. A fiber waiting on 773 a <code class="computeroutput">condition_variable</code> might well wake up a number of times before the 774 desired state is reached. 775 </p></dd> 776</dl> 777</div> 778<p> 779 </p> 780<h5> 781<a name="condition_variable_wait_bridgehead"></a> 782 <span class="phrase"><a name="condition_variable_wait"></a></span> 783 <a class="link" href="conditions.html#condition_variable_wait">Templated 784 member function <code class="computeroutput">wait</code>()</a> 785</h5> 786<p> 787 </p> 788<pre class="programlisting">void <span class="identifier">wait</span><span class="special">(</span> std::unique_lock< mutex > <span class="special">&</span> <span class="identifier">lk</span><span class="special">);</span> 789 790<span class="keyword">template</span><span class="special"><</span> typename <span class="identifier">Pred</span> <span class="special">></span> 791<span class="keyword">void</span> <span class="identifier">wait</span><span class="special">(</span> std::unique_lock< mutex > <span class="special">&</span> <span class="identifier">lk</span><span class="special">,</span> <span class="identifier">Pred</span> <span class="identifier">pred</span><span class="special">);</span> 792</pre> 793<div class="variablelist"> 794<p class="title"><b></b></p> 795<dl class="variablelist"> 796<dt><span class="term">Precondition:</span></dt> 797<dd><p> 798 <code class="computeroutput"><span class="identifier">lk</span></code> is locked by the 799 current fiber, and either no other fiber is currently waiting on <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>, 800 or the execution of the <a href="http://en.cppreference.com/w/cpp/thread/unique_lock/mutex" target="_top"><code class="computeroutput"><span class="identifier">mutex</span><span class="special">()</span></code></a> 801 member function on the <code class="computeroutput"><span class="identifier">lk</span></code> 802 objects supplied in the calls to <code class="computeroutput"><span class="identifier">wait</span></code> 803 in all the fibers currently waiting on <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> would return the same value as 804 <code class="computeroutput"><span class="identifier">lk</span><span class="special">-></span><span class="identifier">mutex</span><span class="special">()</span></code> 805 for this call to <code class="computeroutput"><span class="identifier">wait</span></code>. 806 </p></dd> 807<dt><span class="term">Effects:</span></dt> 808<dd> 809<p> 810 Atomically call <code class="computeroutput"><span class="identifier">lk</span><span class="special">.</span><span class="identifier">unlock</span><span class="special">()</span></code> and blocks the current fiber. The 811 fiber will unblock when notified by a call to <code class="computeroutput"><span class="keyword">this</span><span class="special">-></span><span class="identifier">notify_one</span><span class="special">()</span></code> or <code class="computeroutput"><span class="keyword">this</span><span class="special">-></span><span class="identifier">notify_all</span><span class="special">()</span></code>. When the fiber is unblocked (for 812 whatever reason), the lock is reacquired by invoking <code class="computeroutput"><span class="identifier">lk</span><span class="special">.</span><span class="identifier">lock</span><span class="special">()</span></code> 813 before the call to <code class="computeroutput"><span class="identifier">wait</span></code> 814 returns. The lock is also reacquired by invoking <code class="computeroutput"><span class="identifier">lk</span><span class="special">.</span><span class="identifier">lock</span><span class="special">()</span></code> if the function exits with an exception. 815 The member function accepting <code class="computeroutput"><span class="identifier">pred</span></code> 816 is shorthand for: 817</p> 818<pre class="programlisting"><span class="keyword">while</span> <span class="special">(</span> <span class="special">!</span> <span class="identifier">pred</span><span class="special">()</span> <span class="special">)</span> <span class="special">{</span> 819 <span class="identifier">wait</span><span class="special">(</span> <span class="identifier">lk</span><span class="special">);</span> 820<span class="special">}</span> 821</pre> 822<p> 823 </p> 824</dd> 825<dt><span class="term">Postcondition:</span></dt> 826<dd><p> 827 <code class="computeroutput"><span class="identifier">lk</span></code> is locked by the 828 current fiber. 829 </p></dd> 830<dt><span class="term">Throws:</span></dt> 831<dd><p> 832 <code class="computeroutput"><span class="identifier">fiber_error</span></code> if an error 833 occurs. 834 </p></dd> 835<dt><span class="term">Note:</span></dt> 836<dd><p> 837 The Precondition is a bit dense. It merely states that all the fibers 838 concurrently calling <code class="computeroutput"><span class="identifier">wait</span></code> 839 on <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> 840 must wait on <code class="computeroutput"><span class="identifier">lk</span></code> objects 841 governing the <span class="emphasis"><em>same</em></span> <a class="link" href="mutex_types.html#class_mutex"><code class="computeroutput">mutex</code></a>. Three distinct 842 objects are involved in any <code class="computeroutput">condition_variable::wait()</code> call: the <code class="computeroutput">condition_variable</code> itself, 843 the <code class="computeroutput"><span class="identifier">mutex</span></code> coordinating 844 access between fibers and a local lock object (e.g. <a href="http://en.cppreference.com/w/cpp/thread/unique_lock" target="_top"><code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">unique_lock</span></code></a>). In general, 845 you can partition the lifespan of a given <code class="computeroutput">condition_variable</code> instance 846 into periods with one or more fibers waiting on it, separated by periods 847 when no fibers are waiting on it. When more than one fiber is waiting 848 on that <code class="computeroutput">condition_variable</code>, all must pass lock objects referencing 849 the <span class="emphasis"><em>same</em></span> <code class="computeroutput"><span class="identifier">mutex</span></code> 850 instance. 851 </p></dd> 852</dl> 853</div> 854<p> 855 </p> 856<h5> 857<a name="condition_variable_wait_until_bridgehead"></a> 858 <span class="phrase"><a name="condition_variable_wait_until"></a></span> 859 <a class="link" href="conditions.html#condition_variable_wait_until">Templated 860 member function <code class="computeroutput">wait_until</code>()</a> 861</h5> 862<p> 863 </p> 864<pre class="programlisting"><span class="keyword">template</span><span class="special"><</span> typename <span class="identifier">Clock</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">Duration</span> <span class="special">></span> 865<span class="identifier">cv_status</span> <span class="identifier">wait_until</span><span class="special">(</span> std::unique_lock< mutex > <span class="special">&</span> <span class="identifier">lk</span><span class="special">,</span> 866 <span class="identifier">std</span><span class="special">::</span><span class="identifier">chrono</span><span class="special">::</span><span class="identifier">time_point</span><span class="special"><</span> <span class="identifier">Clock</span><span class="special">,</span> <span class="identifier">Duration</span> <span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">abs_time</span><span class="special">);</span> 867 868<span class="keyword">template</span><span class="special"><</span> typename <span class="identifier">Clock</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">Duration</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">Pred</span> <span class="special">></span> 869<span class="keyword">bool</span> <span class="identifier">wait_until</span><span class="special">(</span> std::unique_lock< mutex > <span class="special">&</span> <span class="identifier">lk</span><span class="special">,</span> 870 <span class="identifier">std</span><span class="special">::</span><span class="identifier">chrono</span><span class="special">::</span><span class="identifier">time_point</span><span class="special"><</span> <span class="identifier">Clock</span><span class="special">,</span> <span class="identifier">Duration</span> <span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">abs_time</span><span class="special">,</span> 871 <span class="identifier">Pred</span> <span class="identifier">pred</span><span class="special">);</span> 872</pre> 873<div class="variablelist"> 874<p class="title"><b></b></p> 875<dl class="variablelist"> 876<dt><span class="term">Precondition:</span></dt> 877<dd><p> 878 <code class="computeroutput"><span class="identifier">lk</span></code> is locked by the 879 current fiber, and either no other fiber is currently waiting on <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>, 880 or the execution of the <code class="computeroutput"><span class="identifier">mutex</span><span class="special">()</span></code> member function on the <code class="computeroutput"><span class="identifier">lk</span></code> objects supplied in the calls 881 to <code class="computeroutput"><span class="identifier">wait</span></code>, <code class="computeroutput"><span class="identifier">wait_for</span></code> or <code class="computeroutput"><span class="identifier">wait_until</span></code> 882 in all the fibers currently waiting on <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> would return the same value as 883 <code class="computeroutput"><span class="identifier">lk</span><span class="special">.</span><span class="identifier">mutex</span><span class="special">()</span></code> 884 for this call to <code class="computeroutput"><span class="identifier">wait_until</span></code>. 885 </p></dd> 886<dt><span class="term">Effects:</span></dt> 887<dd> 888<p> 889 Atomically call <code class="computeroutput"><span class="identifier">lk</span><span class="special">.</span><span class="identifier">unlock</span><span class="special">()</span></code> and blocks the current fiber. The 890 fiber will unblock when notified by a call to <code class="computeroutput"><span class="keyword">this</span><span class="special">-></span><span class="identifier">notify_one</span><span class="special">()</span></code> or <code class="computeroutput"><span class="keyword">this</span><span class="special">-></span><span class="identifier">notify_all</span><span class="special">()</span></code>, when the system time would be equal 891 to or later than the specified <code class="computeroutput"><span class="identifier">abs_time</span></code>. 892 When the fiber is unblocked (for whatever reason), the lock is reacquired 893 by invoking <code class="computeroutput"><span class="identifier">lk</span><span class="special">.</span><span class="identifier">lock</span><span class="special">()</span></code> 894 before the call to <code class="computeroutput"><span class="identifier">wait_until</span></code> 895 returns. The lock is also reacquired by invoking <code class="computeroutput"><span class="identifier">lk</span><span class="special">.</span><span class="identifier">lock</span><span class="special">()</span></code> if the function exits with an exception. 896 The member function accepting <code class="computeroutput"><span class="identifier">pred</span></code> 897 is shorthand for: 898</p> 899<pre class="programlisting"><span class="keyword">while</span> <span class="special">(</span> <span class="special">!</span> <span class="identifier">pred</span><span class="special">()</span> <span class="special">)</span> <span class="special">{</span> 900 <span class="keyword">if</span> <span class="special">(</span> <span class="identifier">cv_status</span><span class="special">::</span><span class="identifier">timeout</span> <span class="special">==</span> <span class="identifier">wait_until</span><span class="special">(</span> <span class="identifier">lk</span><span class="special">,</span> <span class="identifier">abs_time</span><span class="special">)</span> <span class="special">)</span> 901 <span class="keyword">return</span> <span class="identifier">pred</span><span class="special">();</span> 902<span class="special">}</span> 903<span class="keyword">return</span> <span class="keyword">true</span><span class="special">;</span> 904</pre> 905<p> 906 That is, even if <code class="computeroutput"><span class="identifier">wait_until</span><span class="special">()</span></code> times out, it can still return <code class="computeroutput"><span class="keyword">true</span></code> if <code class="computeroutput"><span class="identifier">pred</span><span class="special">()</span></code> returns <code class="computeroutput"><span class="keyword">true</span></code> 907 at that time. 908 </p> 909</dd> 910<dt><span class="term">Postcondition:</span></dt> 911<dd><p> 912 <code class="computeroutput"><span class="identifier">lk</span></code> is locked by the 913 current fiber. 914 </p></dd> 915<dt><span class="term">Throws:</span></dt> 916<dd><p> 917 <code class="computeroutput"><span class="identifier">fiber_error</span></code> if an error 918 occurs or timeout-related exceptions. 919 </p></dd> 920<dt><span class="term">Returns:</span></dt> 921<dd><p> 922 The overload without <code class="computeroutput"><span class="identifier">pred</span></code> 923 returns <code class="computeroutput"><span class="identifier">cv_status</span><span class="special">::</span><span class="identifier">no_timeout</span></code> if awakened by <code class="computeroutput"><span class="identifier">notify_one</span><span class="special">()</span></code> 924 or <code class="computeroutput"><span class="identifier">notify_all</span><span class="special">()</span></code>, 925 or <code class="computeroutput"><span class="identifier">cv_status</span><span class="special">::</span><span class="identifier">timeout</span></code> if awakened because the system 926 time is past <code class="computeroutput"><span class="identifier">abs_time</span></code>. 927 </p></dd> 928<dt><span class="term">Returns:</span></dt> 929<dd><p> 930 The overload accepting <code class="computeroutput"><span class="identifier">pred</span></code> 931 returns <code class="computeroutput"><span class="keyword">false</span></code> if the call 932 is returning because the time specified by <code class="computeroutput"><span class="identifier">abs_time</span></code> 933 was reached and the predicate returns <code class="computeroutput"><span class="keyword">false</span></code>, 934 <code class="computeroutput"><span class="keyword">true</span></code> otherwise. 935 </p></dd> 936<dt><span class="term">Note:</span></dt> 937<dd><p> 938 See <span class="bold"><strong>Note</strong></span> for <a class="link" href="conditions.html#condition_variable_wait"><code class="computeroutput">condition_variable::wait()</code></a>. 939 </p></dd> 940</dl> 941</div> 942<p> 943 </p> 944<h5> 945<a name="condition_variable_wait_for_bridgehead"></a> 946 <span class="phrase"><a name="condition_variable_wait_for"></a></span> 947 <a class="link" href="conditions.html#condition_variable_wait_for">Templated 948 member function <code class="computeroutput">wait_for</code>()</a> 949</h5> 950<p> 951 </p> 952<pre class="programlisting"><span class="keyword">template</span><span class="special"><</span> typename <span class="identifier">Rep</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">Period</span> <span class="special">></span> 953<span class="identifier">cv_status</span> <span class="identifier">wait_for</span><span class="special">(</span> std::unique_lock< mutex > <span class="special">&</span> <span class="identifier">lk</span><span class="special">,</span> 954 <span class="identifier">std</span><span class="special">::</span><span class="identifier">chrono</span><span class="special">::</span><span class="identifier">duration</span><span class="special"><</span> <span class="identifier">Rep</span><span class="special">,</span> <span class="identifier">Period</span> <span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">rel_time</span><span class="special">);</span> 955 956<span class="keyword">template</span><span class="special"><</span> typename <span class="identifier">Rep</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">Period</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">Pred</span> <span class="special">></span> 957<span class="keyword">bool</span> <span class="identifier">wait_for</span><span class="special">(</span> std::unique_lock< mutex > <span class="special">&</span> <span class="identifier">lk</span><span class="special">,</span> 958 <span class="identifier">std</span><span class="special">::</span><span class="identifier">chrono</span><span class="special">::</span><span class="identifier">duration</span><span class="special"><</span> <span class="identifier">Rep</span><span class="special">,</span> <span class="identifier">Period</span> <span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">rel_time</span><span class="special">,</span> 959 <span class="identifier">Pred</span> <span class="identifier">pred</span><span class="special">);</span> 960</pre> 961<div class="variablelist"> 962<p class="title"><b></b></p> 963<dl class="variablelist"> 964<dt><span class="term">Precondition:</span></dt> 965<dd><p> 966 <code class="computeroutput"><span class="identifier">lk</span></code> is locked by the 967 current fiber, and either no other fiber is currently waiting on <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>, 968 or the execution of the <code class="computeroutput"><span class="identifier">mutex</span><span class="special">()</span></code> member function on the <code class="computeroutput"><span class="identifier">lk</span></code> objects supplied in the calls 969 to <code class="computeroutput"><span class="identifier">wait</span></code>, <code class="computeroutput"><span class="identifier">wait_for</span></code> or <code class="computeroutput"><span class="identifier">wait_until</span></code> 970 in all the fibers currently waiting on <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> would return the same value as 971 <code class="computeroutput"><span class="identifier">lk</span><span class="special">.</span><span class="identifier">mutex</span><span class="special">()</span></code> 972 for this call to <code class="computeroutput"><span class="identifier">wait_for</span></code>. 973 </p></dd> 974<dt><span class="term">Effects:</span></dt> 975<dd> 976<p> 977 Atomically call <code class="computeroutput"><span class="identifier">lk</span><span class="special">.</span><span class="identifier">unlock</span><span class="special">()</span></code> and blocks the current fiber. The 978 fiber will unblock when notified by a call to <code class="computeroutput"><span class="keyword">this</span><span class="special">-></span><span class="identifier">notify_one</span><span class="special">()</span></code> or <code class="computeroutput"><span class="keyword">this</span><span class="special">-></span><span class="identifier">notify_all</span><span class="special">()</span></code>, when a time interval equal to or 979 greater than the specified <code class="computeroutput"><span class="identifier">rel_time</span></code> 980 has elapsed. When the fiber is unblocked (for whatever reason), the 981 lock is reacquired by invoking <code class="computeroutput"><span class="identifier">lk</span><span class="special">.</span><span class="identifier">lock</span><span class="special">()</span></code> before the call to <code class="computeroutput"><span class="identifier">wait</span></code> returns. The lock is also reacquired 982 by invoking <code class="computeroutput"><span class="identifier">lk</span><span class="special">.</span><span class="identifier">lock</span><span class="special">()</span></code> 983 if the function exits with an exception. The <code class="computeroutput"><span class="identifier">wait_for</span><span class="special">()</span></code> member function accepting <code class="computeroutput"><span class="identifier">pred</span></code> is shorthand for: 984</p> 985<pre class="programlisting"><span class="keyword">while</span> <span class="special">(</span> <span class="special">!</span> <span class="identifier">pred</span><span class="special">()</span> <span class="special">)</span> <span class="special">{</span> 986 <span class="keyword">if</span> <span class="special">(</span> <span class="identifier">cv_status</span><span class="special">::</span><span class="identifier">timeout</span> <span class="special">==</span> <span class="identifier">wait_for</span><span class="special">(</span> <span class="identifier">lk</span><span class="special">,</span> <span class="identifier">rel_time</span><span class="special">)</span> <span class="special">)</span> <span class="special">{</span> 987 <span class="keyword">return</span> <span class="identifier">pred</span><span class="special">();</span> 988 <span class="special">}</span> 989<span class="special">}</span> 990<span class="keyword">return</span> <span class="keyword">true</span><span class="special">;</span> 991</pre> 992<p> 993 (except of course that <code class="computeroutput"><span class="identifier">rel_time</span></code> 994 is adjusted for each iteration). The point is that, even if <code class="computeroutput"><span class="identifier">wait_for</span><span class="special">()</span></code> 995 times out, it can still return <code class="computeroutput"><span class="keyword">true</span></code> 996 if <code class="computeroutput"><span class="identifier">pred</span><span class="special">()</span></code> 997 returns <code class="computeroutput"><span class="keyword">true</span></code> at that time. 998 </p> 999</dd> 1000<dt><span class="term">Postcondition:</span></dt> 1001<dd><p> 1002 <code class="computeroutput"><span class="identifier">lk</span></code> is locked by the 1003 current fiber. 1004 </p></dd> 1005<dt><span class="term">Throws:</span></dt> 1006<dd><p> 1007 <code class="computeroutput"><span class="identifier">fiber_error</span></code> if an error 1008 occurs or timeout-related exceptions. 1009 </p></dd> 1010<dt><span class="term">Returns:</span></dt> 1011<dd><p> 1012 The overload without <code class="computeroutput"><span class="identifier">pred</span></code> 1013 returns <code class="computeroutput"><span class="identifier">cv_status</span><span class="special">::</span><span class="identifier">no_timeout</span></code> if awakened by <code class="computeroutput"><span class="identifier">notify_one</span><span class="special">()</span></code> 1014 or <code class="computeroutput"><span class="identifier">notify_all</span><span class="special">()</span></code>, 1015 or <code class="computeroutput"><span class="identifier">cv_status</span><span class="special">::</span><span class="identifier">timeout</span></code> if awakened because at least 1016 <code class="computeroutput"><span class="identifier">rel_time</span></code> has elapsed. 1017 </p></dd> 1018<dt><span class="term">Returns:</span></dt> 1019<dd><p> 1020 The overload accepting <code class="computeroutput"><span class="identifier">pred</span></code> 1021 returns <code class="computeroutput"><span class="keyword">false</span></code> if the call 1022 is returning because at least <code class="computeroutput"><span class="identifier">rel_time</span></code> 1023 has elapsed and the predicate returns <code class="computeroutput"><span class="keyword">false</span></code>, 1024 <code class="computeroutput"><span class="keyword">true</span></code> otherwise. 1025 </p></dd> 1026<dt><span class="term">Note:</span></dt> 1027<dd><p> 1028 See <span class="bold"><strong>Note</strong></span> for <a class="link" href="conditions.html#condition_variable_wait"><code class="computeroutput">condition_variable::wait()</code></a>. 1029 </p></dd> 1030</dl> 1031</div> 1032</div> 1033<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 1034<td align="left"></td> 1035<td align="right"><div class="copyright-footer">Copyright © 2013 Oliver Kowalke<p> 1036 Distributed under the Boost Software License, Version 1.0. (See accompanying 1037 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>) 1038 </p> 1039</div></td> 1040</tr></table> 1041<hr> 1042<div class="spirit-nav"> 1043<a accesskey="p" href="mutex_types.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../synchronization.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="barriers.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a> 1044</div> 1045</body> 1046</html> 1047
