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| 25 | <div class="refentry" lang="en"> |
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| 26 | <a name="condition"></a><div class="titlepage"></div> |
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| 27 | <div class="refnamediv"> |
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| 28 | <h2><span class="refentrytitle">Class condition</span></h2> |
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| 29 | <p>boost::condition — <p>An object of class <a href="condition.html" title="Class condition">condition</a> is a |
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| 30 | synchronization primitive used to cause a thread to wait until a |
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| 31 | particular shared-data condition (or time) is met.</p></p> |
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| 32 | </div> |
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| 33 | <h2 xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="refsynopsisdiv-title">Synopsis</h2> |
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| 34 | <div xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="refsynopsisdiv"><pre class="synopsis"> |
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| 35 | <span class="bold"><strong>class</strong></span> condition : <span class="bold"><strong>private</strong></span> boost::noncopyable <span class="emphasis"><em>// Exposition only</em></span> |
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| 36 | { |
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| 37 | <span class="bold"><strong>public</strong></span>: |
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| 38 | <span class="emphasis"><em>// <a href="condition.html#conditionconstruct-copy-destruct">construct/copy/destruct</a></em></span> |
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| 39 | <a href="condition.html#id2531211-bb">condition</a>(); |
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| 40 | <a href="condition.html#id2604889-bb">~condition</a>(); |
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| 41 | |
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| 42 | <span class="emphasis"><em>// <a href="condition.html#id2616531-bb">notification</a></em></span> |
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| 43 | <span class="type"><span class="bold"><strong>void</strong></span></span> <a href="condition.html#id2534198-bb">notify_one</a>(); |
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| 44 | <span class="type"><span class="bold"><strong>void</strong></span></span> <a href="condition.html#id2617876-bb">notify_all</a>(); |
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| 45 | |
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| 46 | <span class="emphasis"><em>// <a href="condition.html#id2616162-bb">waiting</a></em></span> |
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| 47 | <span class="bold"><strong>template</strong></span><<span class="bold"><strong>typename</strong></span> ScopedLock> <span class="type"><span class="bold"><strong>void</strong></span></span> <a href="condition.html#id2575301-bb">wait</a>(ScopedLock&); |
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| 48 | <span class="bold"><strong>template</strong></span><<span class="bold"><strong>typename</strong></span> ScopedLock, <span class="bold"><strong>typename</strong></span> Pred> <span class="type"><span class="bold"><strong>void</strong></span></span> <a href="condition.html#id2450378-bb">wait</a>(ScopedLock&, Pred); |
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| 49 | <span class="bold"><strong>template</strong></span><<span class="bold"><strong>typename</strong></span> ScopedLock> |
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| 50 | <span class="type"><span class="bold"><strong>bool</strong></span></span> <a href="condition.html#id2592886-bb">timed_wait</a>(ScopedLock&, <span class="bold"><strong>const</strong></span> <a href="xtime.html" title="Struct xtime">boost::xtime</a>&); |
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| 51 | <span class="bold"><strong>template</strong></span><<span class="bold"><strong>typename</strong></span> ScopedLock, <span class="bold"><strong>typename</strong></span> Pred> |
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| 52 | <span class="type"><span class="bold"><strong>bool</strong></span></span> <a href="condition.html#id2529517-bb">timed_wait</a>(ScopedLock&, Pred); |
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| 53 | };</pre></div> |
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| 54 | <div class="refsect1" lang="en"> |
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| 55 | <a name="id2779416"></a><h2>Description</h2> |
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| 56 | <p>A <a href="condition.html" title="Class condition">condition</a> object is always used in |
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| 57 | conjunction with a <a href="threads/concepts.html#threads.concepts.mutexes" title="Mutexes">mutex</a> |
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| 58 | object (an object whose type is a model of a <a href="threads/concepts.html#threads.concepts.Mutex" title="Mutex Concept">Mutex</a> or one of its |
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| 59 | refinements). The mutex object must be locked prior to waiting on the |
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| 60 | condition, which is verified by passing a lock object (an object whose |
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| 61 | type is a model of <a href="threads/concepts.html#threads.concepts.Lock" title="Lock Concept">Lock</a> or |
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| 62 | one of its refinements) to the <a href="condition.html" title="Class condition">condition</a> object's |
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| 63 | wait functions. Upon blocking on the <a href="condition.html" title="Class condition">condition</a> |
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| 64 | object, the thread unlocks the mutex object. When the thread returns |
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| 65 | from a call to one of the <a href="condition.html" title="Class condition">condition</a> object's wait |
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| 66 | functions the mutex object is again locked. The tricky unlock/lock |
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| 67 | sequence is performed automatically by the |
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| 68 | <a href="condition.html" title="Class condition">condition</a> object's wait functions.</p> |
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| 69 | <p>The <a href="condition.html" title="Class condition">condition</a> type is often used to |
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| 70 | implement the Monitor Object and other important patterns (see |
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| 71 | [<span class="citation"><a href="threads.html#threads.bib.SchmidtStalRohnertBuschmann">SchmidtStalRohnertBuschmann</a></span>] and [<span class="citation"><a href="threads.html#threads.bib.Hoare74">Hoare74</a></span>]). Monitors are one |
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| 72 | of the most important patterns for creating reliable multithreaded |
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| 73 | programs.</p> |
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| 74 | <p>See <a href="threads.html#threads.glossary" title="Glossary">Glossary</a> for definitions of <a href="threads.html#threads.glossary.thread-state">thread states</a> |
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| 75 | blocked and ready. Note that "waiting" is a synonym for blocked.</p> |
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| 76 | <div class="refsect2" lang="en"> |
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| 77 | <a name="id2779548"></a><h3> |
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| 78 | <a name="conditionconstruct-copy-destruct"></a><code class="computeroutput">condition</code> construct/copy/destruct</h3> |
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| 79 | <div class="orderedlist"><ol type="1"> |
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| 80 | <li> |
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| 81 | <pre class="literallayout"><a name="id2531211-bb"></a>condition();</pre> |
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| 82 | <p><b xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision"><span class="term">Effects</span></b>: |
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| 83 | |
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| 84 | Constructs a <a href="condition.html" title="Class condition">condition</a> |
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| 85 | object.</p> |
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| 86 | </li> |
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| 87 | <li> |
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| 88 | <pre class="literallayout"><a name="id2604889-bb"></a>~condition();</pre> |
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| 89 | <p><b xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision"><span class="term">Effects</span></b>: |
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| 90 | |
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| 91 | Destroys <code class="computeroutput">*this</code>.</p> |
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| 92 | </li> |
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| 93 | </ol></div> |
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| 94 | </div> |
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| 95 | <div class="refsect2" lang="en"> |
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| 96 | <a name="id2779628"></a><h3> |
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| 97 | <a name="id2616531-bb"></a><code class="computeroutput">condition</code> notification</h3> |
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| 98 | <div class="orderedlist"><ol type="1"> |
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| 99 | <li> |
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| 100 | <pre class="literallayout"><span class="type"><span class="bold"><strong>void</strong></span></span> <a name="id2534198-bb"></a>notify_one();</pre> |
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| 101 | <p><b xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision"><span class="term">Effects</span></b>: |
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| 102 | |
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| 103 | If there is a thread waiting on <code class="computeroutput">*this</code>, |
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| 104 | change that thread's state to ready. Otherwise there is no |
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| 105 | effect.<br><b xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision"><span class="term">Notes</span></b>: |
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| 106 | |
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| 107 | If more than one thread is waiting on <code class="computeroutput">*this</code>, |
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| 108 | it is unspecified which is made ready. After returning to a ready |
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| 109 | state the notified thread must still acquire the mutex again (which |
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| 110 | occurs within the call to one of the <a href="condition.html" title="Class condition">condition</a> |
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| 111 | object's wait functions.)</p> |
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| 112 | </li> |
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| 113 | <li> |
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| 114 | <pre class="literallayout"><span class="type"><span class="bold"><strong>void</strong></span></span> <a name="id2617876-bb"></a>notify_all();</pre> |
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| 115 | <p><b xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision"><span class="term">Effects</span></b>: |
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| 116 | |
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| 117 | Change the state of all threads waiting on |
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| 118 | <code class="computeroutput">*this</code> to ready. If there are no waiting threads, |
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| 119 | <code class="computeroutput">notify_all()</code> has no effect.</p> |
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| 120 | </li> |
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| 121 | </ol></div> |
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| 122 | </div> |
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| 123 | <div class="refsect2" lang="en"> |
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| 124 | <a name="id2779754"></a><h3> |
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| 125 | <a name="id2616162-bb"></a><code class="computeroutput">condition</code> waiting</h3> |
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| 126 | <div class="orderedlist"><ol type="1"> |
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| 127 | <li> |
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| 128 | <pre class="literallayout"><span class="bold"><strong>template</strong></span><<span class="bold"><strong>typename</strong></span> ScopedLock> <span class="type"><span class="bold"><strong>void</strong></span></span> <a name="id2575301-bb"></a>wait(ScopedLock& lock);</pre> |
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| 129 | <p><b xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision"><span class="term">Requires</span></b>: |
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| 130 | |
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| 131 | <code class="computeroutput">ScopedLock</code> meets the <a href="threads/concepts.html#threads.concepts.ScopedLock" title="ScopedLock Concept">ScopedLock</a> |
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| 132 | requirements.<br><b xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision"><span class="term">Effects</span></b>: |
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| 133 | |
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| 134 | Releases the lock on the <a href="threads/concepts.html#threads.concepts.mutexes" title="Mutexes">mutex object</a> |
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| 135 | associated with <code class="computeroutput">lock</code>, blocks the current thread of execution |
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| 136 | until readied by a call to <code class="computeroutput">this->notify_one()</code> |
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| 137 | or<code class="computeroutput"> this->notify_all()</code>, and then reacquires the |
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| 138 | lock.<br><b xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision"><span class="term">Throws</span></b>: |
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| 139 | |
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| 140 | <a href="lock_error.html" title="Class lock_error">lock_error</a> if |
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| 141 | <code class="computeroutput">!lock.locked()</code></p> |
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| 142 | </li> |
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| 143 | <li> |
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| 144 | <pre class="literallayout"><span class="bold"><strong>template</strong></span><<span class="bold"><strong>typename</strong></span> ScopedLock, <span class="bold"><strong>typename</strong></span> Pred> |
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| 145 | <span class="type"><span class="bold"><strong>void</strong></span></span> <a name="id2450378-bb"></a>wait(ScopedLock& lock, Pred pred);</pre> |
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| 146 | <p><b xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision"><span class="term">Requires</span></b>: |
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| 147 | |
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| 148 | <code class="computeroutput">ScopedLock</code> meets the <a href="threads/concepts.html#threads.concepts.ScopedLock" title="ScopedLock Concept">ScopedLock</a> |
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| 149 | requirements and the return from <code class="computeroutput">pred()</code> is |
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| 150 | convertible to <code class="computeroutput">bool</code>.<br><b xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision"><span class="term">Effects</span></b>: |
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| 151 | |
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| 152 | As if: <code class="computeroutput">while (!pred()) |
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| 153 | wait(lock)</code><br><b xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision"><span class="term">Throws</span></b>: |
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| 154 | |
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| 155 | <a href="lock_error.html" title="Class lock_error">lock_error</a> if |
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| 156 | <code class="computeroutput">!lock.locked()</code></p> |
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| 157 | </li> |
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| 158 | <li> |
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| 159 | <pre class="literallayout"><span class="bold"><strong>template</strong></span><<span class="bold"><strong>typename</strong></span> ScopedLock> |
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| 160 | <span class="type"><span class="bold"><strong>bool</strong></span></span> <a name="id2592886-bb"></a>timed_wait(ScopedLock& lock, <span class="bold"><strong>const</strong></span> <a href="xtime.html" title="Struct xtime">boost::xtime</a>& xt);</pre> |
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| 161 | <p><b xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision"><span class="term">Requires</span></b>: |
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| 162 | |
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| 163 | <code class="computeroutput">ScopedLock</code> meets the <a href="threads/concepts.html#threads.concepts.ScopedLock" title="ScopedLock Concept">ScopedLock</a> |
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| 164 | requirements.<br><b xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision"><span class="term">Effects</span></b>: |
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| 165 | |
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| 166 | Releases the lock on the <a href="threads/concepts.html#threads.concepts.mutexes" title="Mutexes">mutex object</a> |
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| 167 | associated with <code class="computeroutput">lock</code>, blocks the current thread of execution |
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| 168 | until readied by a call to <code class="computeroutput">this->notify_one()</code> |
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| 169 | or<code class="computeroutput"> this->notify_all()</code>, or until time <code class="computeroutput">xt</code> |
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| 170 | is reached, and then reacquires the lock.<br><b xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision"><span class="term">Returns</span></b>: |
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| 171 | |
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| 172 | <code class="computeroutput">false</code> if time <code class="computeroutput">xt</code> is reached, |
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| 173 | otherwise <code class="computeroutput">true</code>.<br><b xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision"><span class="term">Throws</span></b>: |
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| 174 | |
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| 175 | <a href="lock_error.html" title="Class lock_error">lock_error</a> if |
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| 176 | <code class="computeroutput">!lock.locked()</code></p> |
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| 177 | </li> |
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| 178 | <li> |
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| 179 | <pre class="literallayout"><span class="bold"><strong>template</strong></span><<span class="bold"><strong>typename</strong></span> ScopedLock, <span class="bold"><strong>typename</strong></span> Pred> |
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| 180 | <span class="type"><span class="bold"><strong>bool</strong></span></span> <a name="id2529517-bb"></a>timed_wait(ScopedLock& lock, Pred pred);</pre> |
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| 181 | <p><b xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision"><span class="term">Requires</span></b>: |
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| 182 | |
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| 183 | <code class="computeroutput">ScopedLock</code> meets the <a href="threads/concepts.html#threads.concepts.ScopedLock" title="ScopedLock Concept">ScopedLock</a> |
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| 184 | requirements and the return from <code class="computeroutput">pred()</code> is |
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| 185 | convertible to <code class="computeroutput">bool</code>.<br><b xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision"><span class="term">Effects</span></b>: |
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| 186 | |
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| 187 | As if: <code class="computeroutput">while (!pred()) { if (!timed_wait(lock, |
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| 188 | xt)) return false; } return true;</code><br><b xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision"><span class="term">Returns</span></b>: |
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| 189 | |
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| 190 | <code class="computeroutput">false</code> if <code class="computeroutput">xt</code> is reached, |
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| 191 | otherwise <code class="computeroutput">true</code>.<br><b xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision"><span class="term">Throws</span></b>: |
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| 192 | |
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| 193 | <a href="lock_error.html" title="Class lock_error">lock_error</a> if |
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| 194 | <code class="computeroutput">!lock.locked()</code></p> |
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| 195 | </li> |
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| 196 | </ol></div> |
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| 197 | </div> |
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| 198 | </div> |
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| 199 | </div> |
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| 200 | <table width="100%"><tr> |
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| 201 | <td align="left"></td> |
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| 202 | <td align="right"><small>Copyright © 2001-2003 William E. Kempf</small></td> |
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| 203 | </tr></table> |
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