ceph/src/boost/libs/fiber/doc/html/fiber/synchronization/conditions.html

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  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><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">&lt;</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">&gt;</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">&lt;</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">&gt;</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">&lt;</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">&gt;</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">&lt;</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">&gt;</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><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><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><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>
 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><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>
 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><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">&lt;</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">&gt;</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">&amp;)</span> <span class="special">=</span> <span class="keyword">delete</span><span class="special">;</span>
 217     condition_variable_any <span class="special">&amp;</span> <span class="keyword">operator</span><span class="special">=(</span> condition_variable_any <span class="keyword">const</span><span class="special">&amp;)</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&lt; typename LockType &gt;
 223     void <span class="identifier">wait</span><span class="special">(</span> LockType <span class="special">&amp;);</span>
 224
 225     <span class="keyword">template</span><span class="special">&lt;</span> typename LockType, typename <span class="identifier">Pred</span> <span class="special">&gt;</span>
 226     <span class="keyword">void</span> <span class="identifier">wait</span><span class="special">(</span> LockType <span class="special">&amp;,</span> <span class="identifier">Pred</span><span class="special">);</span>
 227
 228     <span class="keyword">template</span><span class="special">&lt;</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">&gt;</span>
 229     <span class="identifier">cv_status</span> <span class="identifier">wait_until</span><span class="special">(</span> LockType <span class="special">&amp;,</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">&lt;</span> <span class="identifier">Clock</span><span class="special">,</span> <span class="identifier">Duration</span> <span class="special">&gt;</span> <span class="keyword">const</span><span class="special">&amp;);</span>
 231
 232     <span class="keyword">template</span><span class="special">&lt;</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">&gt;</span>
 233     <span class="keyword">bool</span> <span class="identifier">wait_until</span><span class="special">(</span> LockType <span class="special">&amp;,</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">&lt;</span> <span class="identifier">Clock</span><span class="special">,</span> <span class="identifier">Duration</span> <span class="special">&gt;</span> <span class="keyword">const</span><span class="special">&amp;,</span>
 235                      <span class="identifier">Pred</span><span class="special">);</span>
 236
 237     <span class="keyword">template</span><span class="special">&lt;</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">&gt;</span>
 238     <span class="identifier">cv_status</span> <span class="identifier">wait_for</span><span class="special">(</span> LockType <span class="special">&amp;,</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">&lt;</span> <span class="identifier">Rep</span><span class="special">,</span> <span class="identifier">Period</span> <span class="special">&gt;</span> <span class="keyword">const</span><span class="special">&amp;);</span>
 240
 241     <span class="keyword">template</span><span class="special">&lt;</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">&gt;</span>
 242     <span class="keyword">bool</span> <span class="identifier">wait_for</span><span class="special">(</span> LockType <span class="special">&amp;,</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">&lt;</span> <span class="identifier">Rep</span><span class="special">,</span> <span class="identifier">Period</span> <span class="special">&gt;</span> <span class="keyword">const</span><span class="special">&amp;,</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><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>
 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><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>
 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><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>
 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><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>
 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><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&lt; typename LockType &gt;
 371     void <span class="identifier">wait</span><span class="special">(</span> LockType <span class="special">&amp;</span> <span class="identifier">lk</span><span class="special">);</span>
 372
 373 <span class="keyword">template</span><span class="special">&lt;</span> typename LockType, typename <span class="identifier">Pred</span> <span class="special">&gt;</span>
 374 <span class="keyword">void</span> <span class="identifier">wait</span><span class="special">(</span> LockType <span class="special">&amp;</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>
 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">-&gt;</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">-&gt;</span><span class="identifier">notify_one</span><span class="special">()</span></code> or <code class="computeroutput"><span class="keyword">this</span><span class="special">-&gt;</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><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">&lt;</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">&gt;</span>
 448 <span class="identifier">cv_status</span> <span class="identifier">wait_until</span><span class="special">(</span> LockType <span class="special">&amp;</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">&lt;</span> <span class="identifier">Clock</span><span class="special">,</span> <span class="identifier">Duration</span> <span class="special">&gt;</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">abs_time</span><span class="special">);</span>
 450
 451 <span class="keyword">template</span><span class="special">&lt;</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">&gt;</span>
 452 <span class="keyword">bool</span> <span class="identifier">wait_until</span><span class="special">(</span> LockType <span class="special">&amp;</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">&lt;</span> <span class="identifier">Clock</span><span class="special">,</span> <span class="identifier">Duration</span> <span class="special">&gt;</span> <span class="keyword">const</span><span class="special">&amp;</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>
 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">-&gt;</span><span class="identifier">notify_one</span><span class="special">()</span></code> or <code class="computeroutput"><span class="keyword">this</span><span class="special">-&gt;</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><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">&lt;</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">&gt;</span>
 536 <span class="identifier">cv_status</span> <span class="identifier">wait_for</span><span class="special">(</span> LockType <span class="special">&amp;</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">&lt;</span> <span class="identifier">Rep</span><span class="special">,</span> <span class="identifier">Period</span> <span class="special">&gt;</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">rel_time</span><span class="special">);</span>
 538
 539 <span class="keyword">template</span><span class="special">&lt;</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">&gt;</span>
 540 <span class="keyword">bool</span> <span class="identifier">wait_for</span><span class="special">(</span> LockType <span class="special">&amp;</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">&lt;</span> <span class="identifier">Rep</span><span class="special">,</span> <span class="identifier">Period</span> <span class="special">&gt;</span> <span class="keyword">const</span><span class="special">&amp;</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>
 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">-&gt;</span><span class="identifier">notify_one</span><span class="special">()</span></code> or <code class="computeroutput"><span class="keyword">this</span><span class="special">-&gt;</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><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">&lt;</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">&gt;</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">&amp;)</span> <span class="special">=</span> <span class="keyword">delete</span><span class="special">;</span>
 636     condition_variable <span class="special">&amp;</span> <span class="keyword">operator</span><span class="special">=(</span> condition_variable <span class="keyword">const</span><span class="special">&amp;)</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&lt; mutex &gt; <span class="special">&amp;);</span>
 642
 643     <span class="keyword">template</span><span class="special">&lt;</span> typename <span class="identifier">Pred</span> <span class="special">&gt;</span>
 644     <span class="keyword">void</span> <span class="identifier">wait</span><span class="special">(</span> std::unique_lock&lt; mutex &gt; <span class="special">&amp;,</span> <span class="identifier">Pred</span><span class="special">);</span>
 645
 646     <span class="keyword">template</span><span class="special">&lt;</span> typename <span class="identifier">Clock</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">Duration</span> <span class="special">&gt;</span>
 647     <span class="identifier">cv_status</span> <span class="identifier">wait_until</span><span class="special">(</span> std::unique_lock&lt; mutex &gt; <span class="special">&amp;,</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">&lt;</span> <span class="identifier">Clock</span><span class="special">,</span> <span class="identifier">Duration</span> <span class="special">&gt;</span> <span class="keyword">const</span><span class="special">&amp;);</span>
 649
 650     <span class="keyword">template</span><span class="special">&lt;</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">&gt;</span>
 651     <span class="keyword">bool</span> <span class="identifier">wait_until</span><span class="special">(</span> std::unique_lock&lt; mutex &gt; <span class="special">&amp;,</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">&lt;</span> <span class="identifier">Clock</span><span class="special">,</span> <span class="identifier">Duration</span> <span class="special">&gt;</span> <span class="keyword">const</span><span class="special">&amp;,</span>
 653                      <span class="identifier">Pred</span><span class="special">);</span>
 654
 655     <span class="keyword">template</span><span class="special">&lt;</span> typename <span class="identifier">Rep</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">Period</span> <span class="special">&gt;</span>
 656     <span class="identifier">cv_status</span> <span class="identifier">wait_for</span><span class="special">(</span> std::unique_lock&lt; mutex &gt; <span class="special">&amp;,</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">&lt;</span> <span class="identifier">Rep</span><span class="special">,</span> <span class="identifier">Period</span> <span class="special">&gt;</span> <span class="keyword">const</span><span class="special">&amp;);</span>
 658
 659     <span class="keyword">template</span><span class="special">&lt;</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">&gt;</span>
 660     <span class="keyword">bool</span> <span class="identifier">wait_for</span><span class="special">(</span> std::unique_lock&lt; mutex &gt; <span class="special">&amp;,</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">&lt;</span> <span class="identifier">Rep</span><span class="special">,</span> <span class="identifier">Period</span> <span class="special">&gt;</span> <span class="keyword">const</span><span class="special">&amp;,</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><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>
 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><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>
 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><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>
 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><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>
 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><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&lt; mutex &gt; <span class="special">&amp;</span> <span class="identifier">lk</span><span class="special">);</span>
 789
 790 <span class="keyword">template</span><span class="special">&lt;</span> typename <span class="identifier">Pred</span> <span class="special">&gt;</span>
 791 <span class="keyword">void</span> <span class="identifier">wait</span><span class="special">(</span> std::unique_lock&lt; mutex &gt; <span class="special">&amp;</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>
 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">-&gt;</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">-&gt;</span><span class="identifier">notify_one</span><span class="special">()</span></code> or <code class="computeroutput"><span class="keyword">this</span><span class="special">-&gt;</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><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">&lt;</span> typename <span class="identifier">Clock</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">Duration</span> <span class="special">&gt;</span>
 865 <span class="identifier">cv_status</span> <span class="identifier">wait_until</span><span class="special">(</span> std::unique_lock&lt; mutex &gt; <span class="special">&amp;</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">&lt;</span> <span class="identifier">Clock</span><span class="special">,</span> <span class="identifier">Duration</span> <span class="special">&gt;</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">abs_time</span><span class="special">);</span>
 867
 868 <span class="keyword">template</span><span class="special">&lt;</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">&gt;</span>
 869 <span class="keyword">bool</span> <span class="identifier">wait_until</span><span class="special">(</span> std::unique_lock&lt; mutex &gt; <span class="special">&amp;</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">&lt;</span> <span class="identifier">Clock</span><span class="special">,</span> <span class="identifier">Duration</span> <span class="special">&gt;</span> <span class="keyword">const</span><span class="special">&amp;</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>
 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">-&gt;</span><span class="identifier">notify_one</span><span class="special">()</span></code> or <code class="computeroutput"><span class="keyword">this</span><span class="special">-&gt;</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><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">&lt;</span> typename <span class="identifier">Rep</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">Period</span> <span class="special">&gt;</span>
 953 <span class="identifier">cv_status</span> <span class="identifier">wait_for</span><span class="special">(</span> std::unique_lock&lt; mutex &gt; <span class="special">&amp;</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">&lt;</span> <span class="identifier">Rep</span><span class="special">,</span> <span class="identifier">Period</span> <span class="special">&gt;</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">rel_time</span><span class="special">);</span>
 955
 956 <span class="keyword">template</span><span class="special">&lt;</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">&gt;</span>
 957 <span class="keyword">bool</span> <span class="identifier">wait_for</span><span class="special">(</span> std::unique_lock&lt; mutex &gt; <span class="special">&amp;</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">&lt;</span> <span class="identifier">Rep</span><span class="special">,</span> <span class="identifier">Period</span> <span class="special">&gt;</span> <span class="keyword">const</span><span class="special">&amp;</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>
 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">-&gt;</span><span class="identifier">notify_one</span><span class="special">()</span></code> or <code class="computeroutput"><span class="keyword">this</span><span class="special">-&gt;</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 &#169; 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>
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