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<td >Qt 5.9</td><td ><a href="qtcore-index.html">Qt Core</a></td><td ><a href="qtcore-module.html">C++ Classes</a></td><td >QThreadPool</td></tr></table><table class="buildversion"><tr>
<td id="buildversion" width="100%" align="right">Qt 5.9.4 Reference Documentation</td>
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<h3><a name="toc">Contents</a></h3>
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<li class="level1"><a href="#properties">Properties</a></li>
<li class="level1"><a href="#public-functions">Public Functions</a></li>
<li class="level1"><a href="#static-public-members">Static Public Members</a></li>
<li class="level1"><a href="#details">Detailed Description</a></li>
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<h1 class="title">QThreadPool Class</h1>
<!-- $$$QThreadPool-brief -->
<p>The <a href="qthreadpool.html">QThreadPool</a> class manages a collection of QThreads. <a href="#details">More...</a></p>
<!-- @@@QThreadPool -->
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<tr><td class="memItemLeft rightAlign topAlign"> Header:</td><td class="memItemRight bottomAlign"> <span class="preprocessor">#include <QThreadPool></span>
</td></tr><tr><td class="memItemLeft rightAlign topAlign"> qmake:</td><td class="memItemRight bottomAlign"> QT += core</td></tr><tr><td class="memItemLeft rightAlign topAlign"> Since:</td><td class="memItemRight bottomAlign"> Qt 4.4</td></tr><tr><td class="memItemLeft rightAlign topAlign"> Inherits:</td><td class="memItemRight bottomAlign"> <a href="qobject.html">QObject</a></td></tr></table></div><ul>
<li><a href="qthreadpool-members.html">List of all members, including inherited members</a></li>
<li><a href="qthreadpool-obsolete.html">Obsolete members</a></li>
</ul>
<p><b>Note:</b> All functions in this class are thread-safe.</p>
<a name="properties"></a>
<h2 id="properties">Properties</h2>
<ul>
<li class="fn"><b><a href="qthreadpool.html#activeThreadCount-prop">activeThreadCount</a></b> : const int</li>
<li class="fn"><b><a href="qthreadpool.html#expiryTimeout-prop">expiryTimeout</a></b> : int</li>
<li class="fn"><b><a href="qthreadpool.html#maxThreadCount-prop">maxThreadCount</a></b> : int</li>
</ul>
<ul>
<li class="fn">1 property inherited from <a href="qobject.html#properties">QObject</a></li>
</ul>
<a name="public-functions"></a>
<h2 id="public-functions">Public Functions</h2>
<div class="table"><table class="alignedsummary">
<tr><td class="memItemLeft rightAlign topAlign"> </td><td class="memItemRight bottomAlign"><b><a href="qthreadpool.html#QThreadPool">QThreadPool</a></b>(QObject *<i>parent</i> = Q_NULLPTR)</td></tr>
<tr><td class="memItemLeft rightAlign topAlign"> </td><td class="memItemRight bottomAlign"><b><a href="qthreadpool.html#dtor.QThreadPool">~QThreadPool</a></b>()</td></tr>
<tr><td class="memItemLeft rightAlign topAlign"> int </td><td class="memItemRight bottomAlign"><b><a href="qthreadpool.html#activeThreadCount-prop">activeThreadCount</a></b>() const</td></tr>
<tr><td class="memItemLeft rightAlign topAlign"> void </td><td class="memItemRight bottomAlign"><b><a href="qthreadpool.html#clear">clear</a></b>()</td></tr>
<tr><td class="memItemLeft rightAlign topAlign"> int </td><td class="memItemRight bottomAlign"><b><a href="qthreadpool.html#expiryTimeout-prop">expiryTimeout</a></b>() const</td></tr>
<tr><td class="memItemLeft rightAlign topAlign"> int </td><td class="memItemRight bottomAlign"><b><a href="qthreadpool.html#maxThreadCount-prop">maxThreadCount</a></b>() const</td></tr>
<tr><td class="memItemLeft rightAlign topAlign"> void </td><td class="memItemRight bottomAlign"><b><a href="qthreadpool.html#releaseThread">releaseThread</a></b>()</td></tr>
<tr><td class="memItemLeft rightAlign topAlign"> void </td><td class="memItemRight bottomAlign"><b><a href="qthreadpool.html#reserveThread">reserveThread</a></b>()</td></tr>
<tr><td class="memItemLeft rightAlign topAlign"> void </td><td class="memItemRight bottomAlign"><b><a href="qthreadpool.html#expiryTimeout-prop">setExpiryTimeout</a></b>(int <i>expiryTimeout</i>)</td></tr>
<tr><td class="memItemLeft rightAlign topAlign"> void </td><td class="memItemRight bottomAlign"><b><a href="qthreadpool.html#maxThreadCount-prop">setMaxThreadCount</a></b>(int <i>maxThreadCount</i>)</td></tr>
<tr><td class="memItemLeft rightAlign topAlign"> void </td><td class="memItemRight bottomAlign"><b><a href="qthreadpool.html#start">start</a></b>(QRunnable *<i>runnable</i>, int <i>priority</i> = 0)</td></tr>
<tr><td class="memItemLeft rightAlign topAlign"> bool </td><td class="memItemRight bottomAlign"><b><a href="qthreadpool.html#tryStart">tryStart</a></b>(QRunnable *<i>runnable</i>)</td></tr>
<tr><td class="memItemLeft rightAlign topAlign"> bool </td><td class="memItemRight bottomAlign"><b><a href="qthreadpool.html#tryTake">tryTake</a></b>(QRunnable *<i>runnable</i>)</td></tr>
<tr><td class="memItemLeft rightAlign topAlign"> bool </td><td class="memItemRight bottomAlign"><b><a href="qthreadpool.html#waitForDone">waitForDone</a></b>(int <i>msecs</i> = -1)</td></tr>
</table></div>
<ul>
<li class="fn">32 public functions inherited from <a href="qobject.html#public-functions">QObject</a></li>
</ul>
<a name="static-public-members"></a>
<h2 id="static-public-members">Static Public Members</h2>
<div class="table"><table class="alignedsummary">
<tr><td class="memItemLeft rightAlign topAlign"> QThreadPool *</td><td class="memItemRight bottomAlign"><b><a href="qthreadpool.html#globalInstance">globalInstance</a></b>()</td></tr>
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<ul>
<li class="fn">11 static public members inherited from <a href="qobject.html#static-public-members">QObject</a></li>
</ul>
<h3>Additional Inherited Members</h3>
<ul>
<li class="fn">1 public slot inherited from <a href="qobject.html#public-slots">QObject</a></li>
<li class="fn">2 signals inherited from <a href="qobject.html#signals">QObject</a></li>
<li class="fn">9 protected functions inherited from <a href="qobject.html#protected-functions">QObject</a></li>
</ul>
<a name="details"></a>
<!-- $$$QThreadPool-description -->
<div class="descr">
<h2 id="details">Detailed Description</h2>
<p>The <a href="qthreadpool.html">QThreadPool</a> class manages a collection of QThreads.</p>
<p><a href="qthreadpool.html">QThreadPool</a> manages and recyles individual <a href="qthread.html">QThread</a> objects to help reduce thread creation costs in programs that use threads. Each Qt application has one global <a href="qthreadpool.html">QThreadPool</a> object, which can be accessed by calling <a href="qthreadpool.html#globalInstance">globalInstance</a>().</p>
<p>To use one of the <a href="qthreadpool.html">QThreadPool</a> threads, subclass <a href="qrunnable.html">QRunnable</a> and implement the run() virtual function. Then create an object of that class and pass it to <a href="qthreadpool.html#start">QThreadPool::start</a>().</p>
<pre class="cpp">
<span class="keyword">class</span> HelloWorldTask : <span class="keyword">public</span> <span class="type"><a href="qrunnable.html">QRunnable</a></span>
{
<span class="type">void</span> run()
{
<a href="qtglobal.html#qDebug">qDebug</a>() <span class="operator"><</span><span class="operator"><</span> <span class="string">"Hello world from thread"</span> <span class="operator"><</span><span class="operator"><</span> <span class="type"><a href="qthread.html">QThread</a></span><span class="operator">::</span>currentThread();
}
}
HelloWorldTask <span class="operator">*</span>hello <span class="operator">=</span> <span class="keyword">new</span> HelloWorldTask();
<span class="comment">// QThreadPool takes ownership and deletes 'hello' automatically</span>
<span class="type"><a href="qthreadpool.html#QThreadPool">QThreadPool</a></span><span class="operator">::</span>globalInstance()<span class="operator">-</span><span class="operator">></span>start(hello);
</pre>
<p><a href="qthreadpool.html">QThreadPool</a> deletes the <a href="qrunnable.html">QRunnable</a> automatically by default. Use <a href="qrunnable.html#setAutoDelete">QRunnable::setAutoDelete</a>() to change the auto-deletion flag.</p>
<p><a href="qthreadpool.html">QThreadPool</a> supports executing the same <a href="qrunnable.html">QRunnable</a> more than once by calling <a href="qthreadpool.html#tryStart">tryStart</a>(this) from within <a href="qrunnable.html#run">QRunnable::run</a>(). If autoDelete is enabled the <a href="qrunnable.html">QRunnable</a> will be deleted when the last thread exits the run function. Calling <a href="qthreadpool.html#start">start</a>() multiple times with the same <a href="qrunnable.html">QRunnable</a> when autoDelete is enabled creates a race condition and is not recommended.</p>
<p>Threads that are unused for a certain amount of time will expire. The default expiry timeout is 30000 milliseconds (30 seconds). This can be changed using <a href="qthreadpool.html#expiryTimeout-prop">setExpiryTimeout</a>(). Setting a negative expiry timeout disables the expiry mechanism.</p>
<p>Call <a href="qthreadpool.html#maxThreadCount-prop">maxThreadCount</a>() to query the maximum number of threads to be used. If needed, you can change the limit with <a href="qthreadpool.html#maxThreadCount-prop">setMaxThreadCount</a>(). The default <a href="qthreadpool.html#maxThreadCount-prop">maxThreadCount</a>() is <a href="qthread.html#idealThreadCount">QThread::idealThreadCount</a>(). The <a href="qthreadpool.html#activeThreadCount-prop">activeThreadCount</a>() function returns the number of threads currently doing work.</p>
<p>The <a href="qthreadpool.html#reserveThread">reserveThread</a>() function reserves a thread for external use. Use <a href="qthreadpool.html#releaseThread">releaseThread</a>() when your are done with the thread, so that it may be reused. Essentially, these functions temporarily increase or reduce the active thread count and are useful when implementing time-consuming operations that are not visible to the <a href="qthreadpool.html">QThreadPool</a>.</p>
<p>Note that <a href="qthreadpool.html">QThreadPool</a> is a low-level class for managing threads, see the Qt Concurrent module for higher level alternatives.</p>
</div>
<p><b>See also </b><a href="qrunnable.html">QRunnable</a>.</p>
<!-- @@@QThreadPool -->
<div class="prop">
<h2>Property Documentation</h2>
<!-- $$$activeThreadCount-prop$$$activeThreadCount -->
<h3 class="fn" id="activeThreadCount-prop"><a name="activeThreadCount-prop"></a><span class="name">activeThreadCount</span> : const <span class="type">int</span></h3>
<p>This property represents the number of active threads in the thread pool.</p>
<p><b>Note: </b>It is possible for this function to return a value that is greater than <a href="qthreadpool.html#maxThreadCount-prop">maxThreadCount</a>(). See <a href="qthreadpool.html#reserveThread">reserveThread</a>() for more details.</p><p><b>Access functions:</b></p>
<div class="table"><table class="alignedsummary">
<tr><td class="memItemLeft topAlign rightAlign"> int </td><td class="memItemRight bottomAlign"><span class="name"><b>activeThreadCount</b></span>() const</td></tr>
</table></div>
<p><b>See also </b><a href="qthreadpool.html#reserveThread">reserveThread</a>() and <a href="qthreadpool.html#releaseThread">releaseThread</a>().</p>
<!-- @@@activeThreadCount -->
<!-- $$$expiryTimeout-prop$$$expiryTimeout$$$setExpiryTimeoutint -->
<h3 class="fn" id="expiryTimeout-prop"><a name="expiryTimeout-prop"></a><span class="name">expiryTimeout</span> : <span class="type">int</span></h3>
<p>Threads that are unused for <i>expiryTimeout</i> milliseconds are considered to have expired and will exit. Such threads will be restarted as needed. The default <i>expiryTimeout</i> is 30000 milliseconds (30 seconds). If <i>expiryTimeout</i> is negative, newly created threads will not expire, e.g., they will not exit until the thread pool is destroyed.</p>
<p>Note that setting <i>expiryTimeout</i> has no effect on already running threads. Only newly created threads will use the new <i>expiryTimeout</i>. We recommend setting the <i>expiryTimeout</i> immediately after creating the thread pool, but before calling <a href="qthreadpool.html#start">start</a>().</p>
<p><b>Access functions:</b></p>
<div class="table"><table class="alignedsummary">
<tr><td class="memItemLeft topAlign rightAlign"> int </td><td class="memItemRight bottomAlign"><span class="name"><b>expiryTimeout</b></span>() const</td></tr>
<tr><td class="memItemLeft topAlign rightAlign"> void </td><td class="memItemRight bottomAlign"><span class="name"><b>setExpiryTimeout</b></span>(int <i>expiryTimeout</i>)</td></tr>
</table></div>
<!-- @@@expiryTimeout -->
<!-- $$$maxThreadCount-prop$$$maxThreadCount$$$setMaxThreadCountint -->
<h3 class="fn" id="maxThreadCount-prop"><a name="maxThreadCount-prop"></a><span class="name">maxThreadCount</span> : <span class="type">int</span></h3>
<p>This property represents the maximum number of threads used by the thread pool.</p>
<p><b>Note: </b>The thread pool will always use at least 1 thread, even if <i>maxThreadCount</i> limit is zero or negative.</p><p>The default <i>maxThreadCount</i> is <a href="qthread.html#idealThreadCount">QThread::idealThreadCount</a>().</p>
<p><b>Access functions:</b></p>
<div class="table"><table class="alignedsummary">
<tr><td class="memItemLeft topAlign rightAlign"> int </td><td class="memItemRight bottomAlign"><span class="name"><b>maxThreadCount</b></span>() const</td></tr>
<tr><td class="memItemLeft topAlign rightAlign"> void </td><td class="memItemRight bottomAlign"><span class="name"><b>setMaxThreadCount</b></span>(int <i>maxThreadCount</i>)</td></tr>
</table></div>
<!-- @@@maxThreadCount -->
</div>
<div class="func">
<h2>Member Function Documentation</h2>
<!-- $$$QThreadPool[overload1]$$$QThreadPoolQObject* -->
<h3 class="fn" id="QThreadPool"><a name="QThreadPool"></a>QThreadPool::<span class="name">QThreadPool</span>(<span class="type"><a href="qobject.html#QObject">QObject</a></span> *<i>parent</i> = Q_NULLPTR)</h3>
<p>Constructs a thread pool with the given <i>parent</i>.</p>
<!-- @@@QThreadPool -->
<!-- $$$~QThreadPool[overload1]$$$~QThreadPool -->
<h3 class="fn" id="dtor.QThreadPool"><a name="dtor.QThreadPool"></a>QThreadPool::<span class="name">~QThreadPool</span>()</h3>
<p>Destroys the <a href="qthreadpool.html">QThreadPool</a>. This function will block until all runnables have been completed.</p>
<!-- @@@~QThreadPool -->
<!-- $$$clear[overload1]$$$clear -->
<h3 class="fn" id="clear"><a name="clear"></a><span class="type">void</span> QThreadPool::<span class="name">clear</span>()</h3>
<p>Removes the runnables that are not yet started from the queue. The runnables for which <a href="qrunnable.html#autoDelete">runnable->autoDelete()</a> returns <code>true</code> are deleted.</p>
<p>This function was introduced in Qt 5.2.</p>
<p><b>See also </b><a href="qthreadpool.html#start">start</a>().</p>
<!-- @@@clear -->
<!-- $$$globalInstance[overload1]$$$globalInstance -->
<h3 class="fn" id="globalInstance"><a name="globalInstance"></a><code>[static] </code><span class="type"><a href="qthreadpool.html#QThreadPool">QThreadPool</a></span> *QThreadPool::<span class="name">globalInstance</span>()</h3>
<p>Returns the global <a href="qthreadpool.html">QThreadPool</a> instance.</p>
<!-- @@@globalInstance -->
<!-- $$$releaseThread[overload1]$$$releaseThread -->
<h3 class="fn" id="releaseThread"><a name="releaseThread"></a><span class="type">void</span> QThreadPool::<span class="name">releaseThread</span>()</h3>
<p>Releases a thread previously reserved by a call to <a href="qthreadpool.html#reserveThread">reserveThread</a>().</p>
<p><b>Note: </b>Calling this function without previously reserving a thread temporarily increases <a href="qthreadpool.html#maxThreadCount-prop">maxThreadCount</a>(). This is useful when a thread goes to sleep waiting for more work, allowing other threads to continue. Be sure to call <a href="qthreadpool.html#reserveThread">reserveThread</a>() when done waiting, so that the thread pool can correctly maintain the <a href="qthreadpool.html#activeThreadCount-prop">activeThreadCount</a>().</p><p><b>See also </b><a href="qthreadpool.html#reserveThread">reserveThread</a>().</p>
<!-- @@@releaseThread -->
<!-- $$$reserveThread[overload1]$$$reserveThread -->
<h3 class="fn" id="reserveThread"><a name="reserveThread"></a><span class="type">void</span> QThreadPool::<span class="name">reserveThread</span>()</h3>
<p>Reserves one thread, disregarding <a href="qthreadpool.html#activeThreadCount-prop">activeThreadCount</a>() and <a href="qthreadpool.html#maxThreadCount-prop">maxThreadCount</a>().</p>
<p>Once you are done with the thread, call <a href="qthreadpool.html#releaseThread">releaseThread</a>() to allow it to be reused.</p>
<p><b>Note: </b>This function will always increase the number of active threads. This means that by using this function, it is possible for <a href="qthreadpool.html#activeThreadCount-prop">activeThreadCount</a>() to return a value greater than <a href="qthreadpool.html#maxThreadCount-prop">maxThreadCount</a>() .</p><p><b>See also </b><a href="qthreadpool.html#releaseThread">releaseThread</a>().</p>
<!-- @@@reserveThread -->
<!-- $$$start[overload1]$$$startQRunnable*int -->
<h3 class="fn" id="start"><a name="start"></a><span class="type">void</span> QThreadPool::<span class="name">start</span>(<span class="type"><a href="qrunnable.html">QRunnable</a></span> *<i>runnable</i>, <span class="type">int</span> <i>priority</i> = 0)</h3>
<p>Reserves a thread and uses it to run <i>runnable</i>, unless this thread will make the current thread count exceed <a href="qthreadpool.html#maxThreadCount-prop">maxThreadCount</a>(). In that case, <i>runnable</i> is added to a run queue instead. The <i>priority</i> argument can be used to control the run queue's order of execution.</p>
<p>Note that the thread pool takes ownership of the <i>runnable</i> if <a href="qrunnable.html#autoDelete">runnable->autoDelete()</a> returns <code>true</code>, and the <i>runnable</i> will be deleted automatically by the thread pool after the <a href="qrunnable.html#run">runnable->run()</a> returns. If <a href="qrunnable.html#autoDelete">runnable->autoDelete()</a> returns <code>false</code>, ownership of <i>runnable</i> remains with the caller. Note that changing the auto-deletion on <i>runnable</i> after calling this functions results in undefined behavior.</p>
<!-- @@@start -->
<!-- $$$tryStart[overload1]$$$tryStartQRunnable* -->
<h3 class="fn" id="tryStart"><a name="tryStart"></a><span class="type">bool</span> QThreadPool::<span class="name">tryStart</span>(<span class="type"><a href="qrunnable.html">QRunnable</a></span> *<i>runnable</i>)</h3>
<p>Attempts to reserve a thread to run <i>runnable</i>.</p>
<p>If no threads are available at the time of calling, then this function does nothing and returns <code>false</code>. Otherwise, <i>runnable</i> is run immediately using one available thread and this function returns <code>true</code>.</p>
<p>Note that the thread pool takes ownership of the <i>runnable</i> if <a href="qrunnable.html#autoDelete">runnable->autoDelete()</a> returns <code>true</code>, and the <i>runnable</i> will be deleted automatically by the thread pool after the <a href="qrunnable.html#run">runnable->run()</a> returns. If <a href="qrunnable.html#autoDelete">runnable->autoDelete()</a> returns <code>false</code>, ownership of <i>runnable</i> remains with the caller. Note that changing the auto-deletion on <i>runnable</i> after calling this function results in undefined behavior.</p>
<!-- @@@tryStart -->
<!-- $$$tryTake[overload1]$$$tryTakeQRunnable* -->
<h3 class="fn" id="tryTake"><a name="tryTake"></a><span class="type">bool</span> QThreadPool::<span class="name">tryTake</span>(<span class="type"><a href="qrunnable.html">QRunnable</a></span> *<i>runnable</i>)</h3>
<p>Attempts to remove the specified <i>runnable</i> from the queue if it is not yet started. If the runnable had not been started, returns <code>true</code>, and ownership of <i>runnable</i> is transferred to the caller (even when <code>runnable->autoDelete() == true</code>). Otherwise returns <code>false</code>.</p>
<p><b>Note: </b>If <code>runnable->autoDelete() == true</code>, this function may remove the wrong runnable. This is known as the <a href="https://en.wikipedia.org/wiki/ABA_problem">ABA problem</a>: the original <i>runnable</i> may already have executed and has since been deleted. The memory is re-used for another runnable, which then gets removed instead of the intended one. For this reason, we recommend calling this function only for runnables that are not auto-deleting.</p><p>This function was introduced in Qt 5.9.</p>
<p><b>See also </b><a href="qthreadpool.html#start">start</a>() and <a href="qrunnable.html#autoDelete">QRunnable::autoDelete</a>().</p>
<!-- @@@tryTake -->
<!-- $$$waitForDone[overload1]$$$waitForDoneint -->
<h3 class="fn" id="waitForDone"><a name="waitForDone"></a><span class="type">bool</span> QThreadPool::<span class="name">waitForDone</span>(<span class="type">int</span> <i>msecs</i> = -1)</h3>
<p>Waits up to <i>msecs</i> milliseconds for all threads to exit and removes all threads from the thread pool. Returns <code>true</code> if all threads were removed; otherwise it returns <code>false</code>. If <i>msecs</i> is -1 (the default), the timeout is ignored (waits for the last thread to exit).</p>
<!-- @@@waitForDone -->
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<acronym title="Copyright">©</acronym> 2017 The Qt Company Ltd.
Documentation contributions included herein are the copyrights of
their respective owners.<br> The documentation provided herein is licensed under the terms of the <a href="http://www.gnu.org/licenses/fdl.html">GNU Free Documentation License version 1.3</a> as published by the Free Software Foundation.<br> Qt and respective logos are trademarks of The Qt Company Ltd. in Finland and/or other countries worldwide. All other trademarks are property
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Mageia
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6
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x86_64
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media
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core-updates
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by-pkgid
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dbf69eaa13c86c67c80d31d9cbb7847c
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files
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819
