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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 >QThreadStorage</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="#public-functions">Public Functions</a></li>
<li class="level1"><a href="#details">Detailed Description</a></li>
<li class="level2"><a href="#caveats">Caveats</a></li>
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<h1 class="title">QThreadStorage Class</h1>
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<p>The <a href="qthreadstorage.html">QThreadStorage</a> class provides per-thread data storage. <a href="#details">More...</a></p>
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<tr><td class="memItemLeft rightAlign topAlign"> Header:</td><td class="memItemRight bottomAlign"> <span class="preprocessor">#include <QThreadStorage></span>
</td></tr><tr><td class="memItemLeft rightAlign topAlign"> qmake:</td><td class="memItemRight bottomAlign"> QT += core</td></tr></table></div><ul>
<li><a href="qthreadstorage-members.html">List of all members, including inherited members</a></li>
</ul>
<p><b>Note:</b> All functions in this class are thread-safe.</p>
<a name="public-functions"></a>
<h2 id="public-functions">Public Functions</h2>
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<tr><td class="memItemLeft rightAlign topAlign"> </td><td class="memItemRight bottomAlign"><b><a href="qthreadstorage.html#QThreadStorage">QThreadStorage</a></b>()</td></tr>
<tr><td class="memItemLeft rightAlign topAlign"> </td><td class="memItemRight bottomAlign"><b><a href="qthreadstorage.html#dtor.QThreadStorage">~QThreadStorage</a></b>()</td></tr>
<tr><td class="memItemLeft rightAlign topAlign"> bool </td><td class="memItemRight bottomAlign"><b><a href="qthreadstorage.html#hasLocalData">hasLocalData</a></b>() const</td></tr>
<tr><td class="memItemLeft rightAlign topAlign"> T &</td><td class="memItemRight bottomAlign"><b><a href="qthreadstorage.html#localData">localData</a></b>()</td></tr>
<tr><td class="memItemLeft rightAlign topAlign"> T </td><td class="memItemRight bottomAlign"><b><a href="qthreadstorage.html#localData-1">localData</a></b>() const</td></tr>
<tr><td class="memItemLeft rightAlign topAlign"> void </td><td class="memItemRight bottomAlign"><b><a href="qthreadstorage.html#setLocalData">setLocalData</a></b>(T <i>data</i>)</td></tr>
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<h2 id="details">Detailed Description</h2>
<p>The <a href="qthreadstorage.html">QThreadStorage</a> class provides per-thread data storage.</p>
<p><a href="qthreadstorage.html">QThreadStorage</a> is a template class that provides per-thread data storage.</p>
<p>The <a href="qthreadstorage.html#setLocalData">setLocalData</a>() function stores a single thread-specific value for the calling thread. The data can be accessed later using <a href="qthreadstorage.html#localData">localData</a>().</p>
<p>The <a href="qthreadstorage.html#hasLocalData">hasLocalData</a>() function allows the programmer to determine if data has previously been set using the <a href="qthreadstorage.html#setLocalData">setLocalData</a>() function. This is also useful for lazy initializiation.</p>
<p>If T is a pointer type, <a href="qthreadstorage.html">QThreadStorage</a> takes ownership of the data (which must be created on the heap with <code>new</code>) and deletes it when the thread exits, either normally or via termination.</p>
<p>For example, the following code uses <a href="qthreadstorage.html">QThreadStorage</a> to store a single cache for each thread that calls the cacheObject() and removeFromCache() functions. The cache is automatically deleted when the calling thread exits.</p>
<pre class="cpp">
<span class="type"><a href="qthreadstorage.html#QThreadStorage">QThreadStorage</a></span><span class="operator"><</span><span class="type"><a href="qcache.html">QCache</a></span><span class="operator"><</span><span class="type"><a href="qstring.html">QString</a></span><span class="operator">,</span> SomeClass<span class="operator">></span> <span class="operator">></span> caches;
<span class="type">void</span> cacheObject(<span class="keyword">const</span> <span class="type"><a href="qstring.html">QString</a></span> <span class="operator">&</span>key<span class="operator">,</span> SomeClass <span class="operator">*</span>object)
{
caches<span class="operator">.</span>localData()<span class="operator">.</span>insert(key<span class="operator">,</span> object);
}
<span class="type">void</span> removeFromCache(<span class="keyword">const</span> <span class="type"><a href="qstring.html">QString</a></span> <span class="operator">&</span>key)
{
<span class="keyword">if</span> (<span class="operator">!</span>caches<span class="operator">.</span>hasLocalData())
<span class="keyword">return</span>;
caches<span class="operator">.</span>localData()<span class="operator">.</span>remove(key);
}
</pre>
<a name="caveats"></a>
<h3 >Caveats</h3>
<ul>
<li>The <a href="qthreadstorage.html">QThreadStorage</a> destructor does not delete per-thread data. <a href="qthreadstorage.html">QThreadStorage</a> only deletes per-thread data when the thread exits or when <a href="qthreadstorage.html#setLocalData">setLocalData</a>() is called multiple times.</li>
<li><a href="qthreadstorage.html">QThreadStorage</a> can be used to store data for the <code>main()</code> thread. <a href="qthreadstorage.html">QThreadStorage</a> deletes all data set for the <code>main()</code> thread when <a href="../qtwidgets/qapplication.html">QApplication</a> is destroyed, regardless of whether or not the <code>main()</code> thread has actually finished.</li>
</ul>
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<p><b>See also </b><a href="qthread.html">QThread</a>.</p>
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<h2>Member Function Documentation</h2>
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<h3 class="fn" id="QThreadStorage"><a name="QThreadStorage"></a>QThreadStorage::<span class="name">QThreadStorage</span>()</h3>
<p>Constructs a new per-thread data storage object.</p>
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<h3 class="fn" id="dtor.QThreadStorage"><a name="dtor.QThreadStorage"></a>QThreadStorage::<span class="name">~QThreadStorage</span>()</h3>
<p>Destroys the per-thread data storage object.</p>
<p>Note: The per-thread data stored is not deleted. Any data left in <a href="qthreadstorage.html">QThreadStorage</a> is leaked. Make sure that all threads using <a href="qthreadstorage.html">QThreadStorage</a> have exited before deleting the <a href="qthreadstorage.html">QThreadStorage</a>.</p>
<p><b>See also </b><a href="qthreadstorage.html#hasLocalData">hasLocalData</a>().</p>
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<h3 class="fn" id="hasLocalData"><a name="hasLocalData"></a><span class="type">bool</span> QThreadStorage::<span class="name">hasLocalData</span>() const</h3>
<p>If T is a pointer type, returns <code>true</code> if the calling thread has non-zero data available.</p>
<p>If T is a value type, returns whether the data has already been constructed by calling <a href="qthreadstorage.html#setLocalData">setLocalData</a> or <a href="qthreadstorage.html#localData">localData</a>.</p>
<p><b>See also </b><a href="qthreadstorage.html#localData">localData</a>().</p>
<!-- @@@hasLocalData -->
<!-- $$$localData[overload1]$$$localData -->
<h3 class="fn" id="localData"><a name="localData"></a><span class="type">T</span> &QThreadStorage::<span class="name">localData</span>()</h3>
<p>Returns a reference to the data that was set by the calling thread.</p>
<p>If no data has been set, this will create a default constructed instance of type T.</p>
<p><b>See also </b><a href="qthreadstorage.html#setLocalData">setLocalData</a>() and <a href="qthreadstorage.html#hasLocalData">hasLocalData</a>().</p>
<!-- @@@localData -->
<!-- $$$localData$$$localData -->
<h3 class="fn" id="localData-1"><a name="localData-1"></a><span class="type">T</span> QThreadStorage::<span class="name">localData</span>() const</h3>
<p>This is an overloaded function.</p>
<p>Returns a copy of the data that was set by the calling thread.</p>
<p><b>See also </b><a href="qthreadstorage.html#hasLocalData">hasLocalData</a>().</p>
<!-- @@@localData -->
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<h3 class="fn" id="setLocalData"><a name="setLocalData"></a><span class="type">void</span> QThreadStorage::<span class="name">setLocalData</span>(<span class="type">T</span> <i>data</i>)</h3>
<p>Sets the local data for the calling thread to <i>data</i>. It can be accessed later using the <a href="qthreadstorage.html#localData">localData</a>() functions.</p>
<p>If T is a pointer type, <a href="qthreadstorage.html">QThreadStorage</a> takes ownership of the data and deletes it automatically either when the thread exits (either normally or via termination) or when setLocalData() is called again.</p>
<p><b>See also </b><a href="qthreadstorage.html#localData">localData</a>() and <a href="qthreadstorage.html#hasLocalData">hasLocalData</a>().</p>
<!-- @@@setLocalData -->
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