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<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="mutex.html" title="cpp/thread/mutex"><span class="t-lines"><span>mutex</span></span></a></div><div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="recursive_mutex.html" title="cpp/thread/recursive mutex"><span class="t-lines"><span>recursive_mutex</span></span></a></div><div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="shared_mutex.html" title="cpp/thread/shared mutex"><span class="t-lines"><span>shared_mutex</span></span></a></div><div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx17">(C++17)</span></span></span></div></div></td></tr>
</table></div></td><td><div><table class="t-nv-begin" cellpadding="0" style="">
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="timed_mutex.html" title="cpp/thread/timed mutex"><span class="t-lines"><span>timed_mutex</span></span></a></div><div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="recursive_timed_mutex.html" title="cpp/thread/recursive timed mutex"><span class="t-lines"><span>recursive_timed_mutex</span></span></a></div><div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="shared_timed_mutex.html" title="cpp/thread/shared timed mutex"><span class="t-lines"><span>shared_timed_mutex</span></span></a></div><div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx14">(C++14)</span></span></span></div></div></td></tr>
</table></div></td></tr>
<tr class="t-nv-h2"><td colspan="5"> Generic lock management</td></tr>
<tr class="t-nv-col-table"><td><div><table class="t-nv-begin" cellpadding="0" style="">
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="lock_guard.html" title="cpp/thread/lock guard"><span class="t-lines"><span>lock_guard</span></span></a></div><div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="unique_lock.html" title="cpp/thread/unique lock"><span class="t-lines"><span>unique_lock</span></span></a></div><div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="shared_lock.html" title="cpp/thread/shared lock"><span class="t-lines"><span>shared_lock</span></span></a></div><div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx14">(C++14)</span></span></span></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="lock_tag_t.html" title="cpp/thread/lock tag t"><span class="t-lines"><span>defer_lock_t</span><span>try_to_lock_t</span><span>adopt_lock_t</span></span></a></div><div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div></div></td></tr>
</table></div></td><td><div><table class="t-nv-begin" cellpadding="0" style="">
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="lock.html" title="cpp/thread/lock"><span class="t-lines"><span>lock</span></span></a></div><div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="try_lock.html" title="cpp/thread/try lock"><span class="t-lines"><span>try_lock</span></span></a></div><div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="lock_tag.html" title="cpp/thread/lock tag"><span class="t-lines"><span>defer_lock</span><span>try_to_lock</span><span>adopt_lock</span></span></a></div><div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="once_flag.html" title="cpp/thread/once flag"><span class="t-lines"><span>once_flag</span></span></a></div><div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="call_once.html" title="cpp/thread/call once"><span class="t-lines"><span>call_once</span></span></a></div><div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div></div></td></tr>
</table></div></td></tr>
<tr class="t-nv-h1"><td colspan="5"> Condition variables</td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><strong class="selflink"><span class="t-lines"><span>condition_variable</span></span></strong></div><div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="condition_variable_any.html" title="cpp/thread/condition variable any"><span class="t-lines"><span>condition_variable_any</span></span></a></div><div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="notify_all_at_thread_exit.html" title="cpp/thread/notify all at thread exit"><span class="t-lines"><span>notify_all_at_thread_exit</span></span></a></div><div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="cv_status.html" title="cpp/thread/cv status"><span class="t-lines"><span>cv_status</span></span></a></div><div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div></div></td></tr>
<tr class="t-nv-h1"><td colspan="5"> Futures</td></tr>
<tr class="t-nv-col-table"><td><div><table class="t-nv-begin" cellpadding="0" style="">
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="promise.html" title="cpp/thread/promise"><span class="t-lines"><span>promise</span></span></a></div><div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="future.html" title="cpp/thread/future"><span class="t-lines"><span>future</span></span></a></div><div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="shared_future.html" title="cpp/thread/shared future"><span class="t-lines"><span>shared_future</span></span></a></div><div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="packaged_task.html" title="cpp/thread/packaged task"><span class="t-lines"><span>packaged_task</span></span></a></div><div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="async.html" title="cpp/thread/async"><span class="t-lines"><span>async</span></span></a></div><div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div></div></td></tr>
</table></div></td><td><div><table class="t-nv-begin" cellpadding="0" style="">
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="launch.html" title="cpp/thread/launch"><span class="t-lines"><span>launch</span></span></a></div><div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="future_status.html" title="cpp/thread/future status"><span class="t-lines"><span>future_status</span></span></a></div><div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="future_error.html" title="cpp/thread/future error"><span class="t-lines"><span>future_error</span></span></a></div><div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="future_category.html" title="cpp/thread/future category"><span class="t-lines"><span>future_category</span></span></a></div><div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="future_errc.html" title="cpp/thread/future errc"><span class="t-lines"><span>future_errc</span></span></a></div><div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div></div></td></tr>
</table></div></td></tr>
</table></div><div><span class="editsection noprint plainlinks" title="Edit this template"><a rel="nofollow" class="external text" href="http://en.cppreference.com/mwiki/index.php?title=Template:cpp/thread/navbar_content&action=edit">[edit]</a></span></div></div></div></div><div class="t-navbar-sep"> </div><div class="t-navbar-head"><strong class="selflink"><tt>std::condition_variable</tt></strong><div class="t-navbar-menu"><div><div><table class="t-nv-begin" cellpadding="0" style="">
<tr class="t-nv-h1"><td colspan="5"> Member functions</td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="condition_variable/condition_variable.html" title="cpp/thread/condition variable/condition variable"><span class="t-lines"><span>condition_variable::condition_variable</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="condition_variable/~condition_variable.html" title="cpp/thread/condition variable/~condition variable"><span class="t-lines"><span>condition_variable::~condition_variable</span></span></a></div></div></td></tr>
<tr class="t-nv-h2"><td colspan="5"> Notification</td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="condition_variable/notify_one.html" title="cpp/thread/condition variable/notify one"><span class="t-lines"><span>condition_variable::notify_one</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="condition_variable/notify_all.html" title="cpp/thread/condition variable/notify all"><span class="t-lines"><span>condition_variable::notify_all</span></span></a></div></div></td></tr>
<tr class="t-nv-h2"><td colspan="5"> Waiting</td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="condition_variable/wait.html" title="cpp/thread/condition variable/wait"><span class="t-lines"><span>condition_variable::wait</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="condition_variable/wait_for.html" title="cpp/thread/condition variable/wait for"><span class="t-lines"><span>condition_variable::wait_for</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="condition_variable/wait_until.html" title="cpp/thread/condition variable/wait until"><span class="t-lines"><span>condition_variable::wait_until</span></span></a></div></div></td></tr>
<tr class="t-nv-h2"><td colspan="5"> Native handle</td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="condition_variable/native_handle.html" title="cpp/thread/condition variable/native handle"><span class="t-lines"><span>condition_variable::native handle</span></span></a></div></div></td></tr>
</table></div><div><span class="editsection noprint plainlinks" title="Edit this template"><a rel="nofollow" class="external text" href="http://en.cppreference.com/mwiki/index.php?title=Template:cpp/thread/condition_variable/navbar_content&action=edit">[edit]</a></span></div></div></div></div><div class="t-navbar-sep"> </div></div>
<table class="t-dcl-begin"><tbody>
<tr class="t-dsc-header">
<td> <div>Defined in header <code><a href="../header/condition_variable.html" title="cpp/header/condition variable"><condition_variable></a></code>
</div></td>
<td></td>
<td></td>
</tr>
<tr class="t-dcl t-since-cxx11">
<td> <div><span class="mw-geshi cpp source-cpp"><span class="kw1">class</span> condition_variable<span class="sy4">;</span></span></div></td>
<td class="t-dcl-nopad"> </td>
<td> <span class="t-mark-rev t-since-cxx11">(since C++11)</span> </td>
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<p>The <code>condition_variable</code> class is a synchronization primitive that can be used to block a thread, or multiple threads at the same time, until another thread both modifies a shared variable (the <i>condition</i>), and notifies the <code>condition_variable</code>.
</p><p>The thread that intends to modify the variable has to
</p>
<ol><li> acquire a <code>std::mutex</code> (typically via <span class="t-lc">std::lock_guard</span>)
</li><li> perform the modification while the lock is held
</li><li> execute <span class="t-lc">notify_one</span> or <span class="t-lc">notify_all</span> on the <code>std::condition_variable</code> (the lock does not need to be held for notification)
</li></ol>
<p>Even if the shared variable is atomic, it must be modified under the mutex in order to correctly publish the modification to the waiting thread.
</p><p>Any thread that intends to wait on <code>std::condition_variable</code> has to
</p>
<ol><li> acquire a <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="unique_lock.html"><span class="kw1845">std::<span class="me2">unique_lock</span></span></a><span class="sy1"><</span><a href="mutex.html"><span class="kw1832">std::<span class="me2">mutex</span></span></a><span class="sy1">></span></span></span>, on the same mutex as used to protect the shared variable
</li><li> execute <span class="t-lc">wait</span>, <span class="t-lc">wait_for</span>, or <span class="t-lc">wait_until</span>. The wait operations atomically release the mutex and suspend the execution of the thread.
</li><li> When the condition variable is notified, a timeout expires, or a <a href="http://en.wikipedia.com/wiki/Spurious_wakeup" class="extiw" title="enwiki:Spurious wakeup">spurious wakeup</a> occurs, the thread is awakened, and the mutex is atomically reacquired. The thread should then check the condition and resume waiting if the wake up was spurious.
</li></ol>
<p><code>std::condition_variable</code> works only with <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="unique_lock.html"><span class="kw1845">std::<span class="me2">unique_lock</span></span></a><span class="sy1"><</span><a href="mutex.html"><span class="kw1832">std::<span class="me2">mutex</span></span></a><span class="sy1">></span></span></span>; this restriction allows for maximal efficiency on some platforms. <span class="t-lc">std::condition_variable_any</span> provides a condition variable that works with any <a href="../concept/BasicLockable.html" title="cpp/concept/BasicLockable"><code>BasicLockable</code></a> object.
</p><p>Condition variables permit concurrent invocation of the <span class="t-lc">wait</span>, <span class="t-lc">wait_for</span>, <span class="t-lc">wait_until</span>, <span class="t-lc">notify_one</span> and <span class="t-lc">notify_all</span> member functions.
</p><p>The class <code>std::condition_variable</code> is a <a href="../concept/StandardLayoutType.html" title="cpp/concept/StandardLayoutType"><code>StandardLayoutType</code></a>. It is not <a href="../concept/CopyConstructible.html" title="cpp/concept/CopyConstructible"><code>CopyConstructible</code></a>, <a href="../concept/MoveConstructible.html" title="cpp/concept/MoveConstructible"><code>MoveConstructible</code></a>, <a href="../concept/CopyAssignable.html" title="cpp/concept/CopyAssignable"><code>CopyAssignable</code></a>, <a href="../concept/MoveAssignable.html" title="cpp/concept/MoveAssignable"><code>MoveAssignable</code></a>.
</p>
<table id="toc" class="toc"><tr><td><div id="toctitle"><h2>Contents</h2></div>
<ul>
<li class="toclevel-1 tocsection-1"><a href="condition_variable.html#Member_types"><span class="tocnumber">1</span> <span class="toctext">Member types</span></a></li>
<li class="toclevel-1 tocsection-2"><a href="condition_variable.html#Member_functions"><span class="tocnumber">2</span> <span class="toctext">Member functions</span></a>
<ul>
<li class="toclevel-2"><a href="condition_variable.html#Notification"><span class="tocnumber">2.1</span> <span class="toctext">Notification</span></a></li>
<li class="toclevel-2"><a href="condition_variable.html#Waiting"><span class="tocnumber">2.2</span> <span class="toctext">Waiting</span></a></li>
<li class="toclevel-2"><a href="condition_variable.html#Native_handle"><span class="tocnumber">2.3</span> <span class="toctext">Native handle</span></a></li>
</ul>
</li>
<li class="toclevel-1 tocsection-3"><a href="condition_variable.html#Example"><span class="tocnumber">3</span> <span class="toctext">Example</span></a></li>
</ul>
</td></tr></table>
<h3><span class="editsection">[<a href="http://en.cppreference.com/mwiki/index.php?title=cpp/thread/condition_variable&action=edit&section=1" title="Edit section: Member types">edit</a>]</span> <span class="mw-headline" id="Member_types">Member types</span></h3>
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<td> Member type
</td>
<td> Definition
</td></tr>
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<td> <code>native_handle_type</code>
</td>
<td> <i>implementation-defined</i>
</td></tr>
</table>
<h3><span class="editsection">[<a href="http://en.cppreference.com/mwiki/index.php?title=cpp/thread/condition_variable&action=edit&section=2" title="Edit section: Member functions">edit</a>]</span> <span class="mw-headline" id="Member_functions">Member functions</span></h3>
<table class="t-dsc-begin">
<tr class="t-dsc">
<td> <div class="t-dsc-member-div t-dsc-member-nobold-div"><div><a href="condition_variable/condition_variable.html" title="cpp/thread/condition variable/condition variable"> <span class="t-lines"><span>(constructor)</span></span></a></div></div>
</td>
<td> constructs the object <br /> <span class="t-mark">(public member function)</span> <span class="editsection noprint plainlinks" title="Edit this template"><a rel="nofollow" class="external text" href="http://en.cppreference.com/mwiki/index.php?title=Template:cpp/thread/condition_variable/dsc_constructor&action=edit">[edit]</a></span>
</td></tr>
<tr class="t-dsc">
<td> <div class="t-dsc-member-div t-dsc-member-nobold-div"><div><a href="condition_variable/~condition_variable.html" title="cpp/thread/condition variable/~condition variable"> <span class="t-lines"><span>(destructor)</span></span></a></div></div>
</td>
<td> destructs the object <br /> <span class="t-mark">(public member function)</span> <span class="editsection noprint plainlinks" title="Edit this template"><a rel="nofollow" class="external text" href="http://en.cppreference.com/mwiki/index.php?title=Template:cpp/thread/condition_variable/dsc_destructor&action=edit">[edit]</a></span>
</td></tr>
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<td> <div class="t-dsc-member-div"><div><span class="t-lines"><span>operator=</span></span></div><div><span class="t-lines"><span><span class="t-cmark">[deleted]</span></span></span></div></div>
</td>
<td> not copy-assignable <br /> <span class="t-mark">(public member function)</span> <span class="editsection noprint plainlinks" title="Edit this template"><a rel="nofollow" class="external text" href="http://en.cppreference.com/mwiki/index.php?title=Template:cpp/thread/condition_variable/dsc_operator%3D&action=edit">[edit]</a></span>
</td></tr>
<tr>
<td colspan="2"> <h5> <span class="mw-headline" id="Notification"> Notification </span></h5>
</td></tr>
<tr class="t-dsc">
<td> <div class="t-dsc-member-div"><div><a href="condition_variable/notify_one.html" title="cpp/thread/condition variable/notify one"> <span class="t-lines"><span>notify_one</span></span></a></div></div>
</td>
<td> notifies one waiting thread <br /> <span class="t-mark">(public member function)</span> <span class="editsection noprint plainlinks" title="Edit this template"><a rel="nofollow" class="external text" href="http://en.cppreference.com/mwiki/index.php?title=Template:cpp/thread/condition_variable/dsc_notify_one&action=edit">[edit]</a></span>
</td></tr>
<tr class="t-dsc">
<td> <div class="t-dsc-member-div"><div><a href="condition_variable/notify_all.html" title="cpp/thread/condition variable/notify all"> <span class="t-lines"><span>notify_all</span></span></a></div></div>
</td>
<td> notifies all waiting threads <br /> <span class="t-mark">(public member function)</span> <span class="editsection noprint plainlinks" title="Edit this template"><a rel="nofollow" class="external text" href="http://en.cppreference.com/mwiki/index.php?title=Template:cpp/thread/condition_variable/dsc_notify_all&action=edit">[edit]</a></span>
</td></tr>
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<td colspan="2"> <h5> <span class="mw-headline" id="Waiting"> Waiting </span></h5>
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<tr class="t-dsc">
<td> <div class="t-dsc-member-div"><div><a href="condition_variable/wait.html" title="cpp/thread/condition variable/wait"> <span class="t-lines"><span>wait</span></span></a></div></div>
</td>
<td> blocks the current thread until the condition variable is woken up <br /> <span class="t-mark">(public member function)</span> <span class="editsection noprint plainlinks" title="Edit this template"><a rel="nofollow" class="external text" href="http://en.cppreference.com/mwiki/index.php?title=Template:cpp/thread/condition_variable/dsc_wait&action=edit">[edit]</a></span>
</td></tr>
<tr class="t-dsc">
<td> <div class="t-dsc-member-div"><div><a href="condition_variable/wait_for.html" title="cpp/thread/condition variable/wait for"> <span class="t-lines"><span>wait_for</span></span></a></div></div>
</td>
<td> blocks the current thread until the condition variable is woken up or after the specified timeout duration <br /> <span class="t-mark">(public member function)</span> <span class="editsection noprint plainlinks" title="Edit this template"><a rel="nofollow" class="external text" href="http://en.cppreference.com/mwiki/index.php?title=Template:cpp/thread/condition_variable/dsc_wait_for&action=edit">[edit]</a></span>
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<td> <div class="t-dsc-member-div"><div><a href="condition_variable/wait_until.html" title="cpp/thread/condition variable/wait until"> <span class="t-lines"><span>wait_until</span></span></a></div></div>
</td>
<td> blocks the current thread until the condition variable is woken up or until specified time point has been reached <br /> <span class="t-mark">(public member function)</span> <span class="editsection noprint plainlinks" title="Edit this template"><a rel="nofollow" class="external text" href="http://en.cppreference.com/mwiki/index.php?title=Template:cpp/thread/condition_variable/dsc_wait_until&action=edit">[edit]</a></span>
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<tr>
<td colspan="2"> <h5> <span class="mw-headline" id="Native_handle"> Native handle </span></h5>
</td></tr>
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<td> <div class="t-dsc-member-div"><div><a href="condition_variable/native_handle.html" title="cpp/thread/condition variable/native handle"> <span class="t-lines"><span>native_handle</span></span></a></div></div>
</td>
<td> returns the native handle <br /> <span class="t-mark">(public member function)</span> <span class="editsection noprint plainlinks" title="Edit this template"><a rel="nofollow" class="external text" href="http://en.cppreference.com/mwiki/index.php?title=Template:cpp/thread/condition_variable/dsc_native_handle&action=edit">[edit]</a></span>
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<h3><span class="editsection">[<a href="http://en.cppreference.com/mwiki/index.php?title=cpp/thread/condition_variable&action=edit&section=3" title="Edit section: Example">edit</a>]</span> <span class="mw-headline" id="Example">Example</span></h3>
<div class="t-example"><p> <code>condition_variable</code> is used in combination with a <span class="t-lc">std::mutex</span> to facilitate inter-thread communication.
</p><div class="t-example-live-link"><div class="coliru-btn coliru-btn-run-init">Run this code</div></div>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="cpp source-cpp"><pre class="de1"><span class="co2">#include <iostream></span>
<span class="co2">#include <string></span>
<span class="co2">#include <thread></span>
<span class="co2">#include <mutex></span>
<span class="co2">#include <condition_variable></span>
 
<a href="mutex.html"><span class="kw1832">std::<span class="me2">mutex</span></span></a> m<span class="sy4">;</span>
std<span class="sy4">::</span><span class="me2">condition_variable</span> cv<span class="sy4">;</span>
<a href="../string/basic_string.html"><span class="kw1072">std::<span class="me2">string</span></span></a> data<span class="sy4">;</span>
<span class="kw4">bool</span> ready <span class="sy1">=</span> <span class="kw2">false</span><span class="sy4">;</span>
<span class="kw4">bool</span> processed <span class="sy1">=</span> <span class="kw2">false</span><span class="sy4">;</span>
 
<span class="kw4">void</span> worker_thread<span class="br0">(</span><span class="br0">)</span>
<span class="br0">{</span>
<span class="co1">// Wait until main() sends data</span>
<a href="unique_lock.html"><span class="kw1845">std::<span class="me2">unique_lock</span></span></a><span class="sy1"><</span><a href="mutex.html"><span class="kw1832">std::<span class="me2">mutex</span></span></a><span class="sy1">></span> lk<span class="br0">(</span>m<span class="br0">)</span><span class="sy4">;</span>
cv.<span class="me1">wait</span><span class="br0">(</span>lk, <span class="br0">[</span><span class="br0">]</span><span class="br0">{</span><span class="kw1">return</span> ready<span class="sy4">;</span><span class="br0">}</span><span class="br0">)</span><span class="sy4">;</span>
 
<span class="co1">// after the wait, we own the lock.</span>
<a href="../io/cout.html"><span class="kw1481">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">"Worker thread is processing data<span class="es1">\n</span>"</span><span class="sy4">;</span>
data <span class="sy2">+</span><span class="sy1">=</span> <span class="st0">" after processing"</span><span class="sy4">;</span>
 
<span class="co1">// Send data back to main()</span>
processed <span class="sy1">=</span> <span class="kw2">true</span><span class="sy4">;</span>
<a href="../io/cout.html"><span class="kw1481">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">"Worker thread signals data processing completed<span class="es1">\n</span>"</span><span class="sy4">;</span>
 
<span class="co1">// Manual unlocking is done before notifying, to avoid waking up</span>
<span class="co1">// the waiting thread only to block again (see notify_one for details)</span>
lk.<span class="me1">unlock</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
cv.<span class="me1">notify_one</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
<span class="br0">}</span>
 
<span class="kw4">int</span> main<span class="br0">(</span><span class="br0">)</span>
<span class="br0">{</span>
<a href="thread.html"><span class="kw1826">std::<span class="me2">thread</span></span></a> worker<span class="br0">(</span>worker_thread<span class="br0">)</span><span class="sy4">;</span>
 
data <span class="sy1">=</span> <span class="st0">"Example data"</span><span class="sy4">;</span>
<span class="co1">// send data to the worker thread</span>
<span class="br0">{</span>
<a href="lock_guard.html"><span class="kw1844">std::<span class="me2">lock_guard</span></span></a><span class="sy1"><</span><a href="mutex.html"><span class="kw1832">std::<span class="me2">mutex</span></span></a><span class="sy1">></span> lk<span class="br0">(</span>m<span class="br0">)</span><span class="sy4">;</span>
ready <span class="sy1">=</span> <span class="kw2">true</span><span class="sy4">;</span>
<a href="../io/cout.html"><span class="kw1481">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">"main() signals data ready for processing<span class="es1">\n</span>"</span><span class="sy4">;</span>
<span class="br0">}</span>
cv.<span class="me1">notify_one</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
 
<span class="co1">// wait for the worker</span>
<span class="br0">{</span>
<a href="unique_lock.html"><span class="kw1845">std::<span class="me2">unique_lock</span></span></a><span class="sy1"><</span><a href="mutex.html"><span class="kw1832">std::<span class="me2">mutex</span></span></a><span class="sy1">></span> lk<span class="br0">(</span>m<span class="br0">)</span><span class="sy4">;</span>
cv.<span class="me1">wait</span><span class="br0">(</span>lk, <span class="br0">[</span><span class="br0">]</span><span class="br0">{</span><span class="kw1">return</span> processed<span class="sy4">;</span><span class="br0">}</span><span class="br0">)</span><span class="sy4">;</span>
<span class="br0">}</span>
<a href="../io/cout.html"><span class="kw1481">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">"Back in main(), data = "</span> <span class="sy1"><<</span> data <span class="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</span><span class="sy4">;</span>
 
worker.<span class="me1">join</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
<span class="br0">}</span></pre></div></div>
<p>Output:
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="text source-text"><pre class="de1">main() signals data ready for processing
Worker thread is processing data
Worker thread signals data processing completed
Back in main(), data = Example data after processing</pre></div></div>
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