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<a href="index.html" class="qtref"><span>Qt Reference Documentation</span></a>
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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 Reference</h1>
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<p>The QThreadStorage class provides per-thread data storage. <a href="#details">More...</a></p>
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<pre class="cpp"> <span class="preprocessor">#include <QThreadStorage></span></pre><p><b>Note:</b> All functions in this class are <a href="threads-reentrancy.html#thread-safe">thread-safe</a>.</p>
<ul>
<li><a href="qthreadstorage-members.html">List of all members, including inherited members</a></li>
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<a name="public-functions"></a>
<h2>Public Functions</h2>
<table class="alignedsummary">
<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-2">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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<div class="descr">
<h2>Detailed Description</h2>
<p>The QThreadStorage class provides per-thread data storage.</p>
<p>QThreadStorage 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, QThreadStorage takes ownership of the data (which must be created on the heap with <tt>new</tt>) and deletes it when the thread exits, either normally or via termination.</p>
<p>For example, the following code uses QThreadStorage 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">QThreadStorage</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 QThreadStorage destructor does not delete per-thread data. QThreadStorage only deletes per-thread data when the thread exits or when <a href="qthreadstorage.html#setLocalData">setLocalData</a>() is called multiple times.</li>
<li>QThreadStorage can be used to store data for the <tt>main()</tt> thread. QThreadStorage deletes all data set for the <tt>main()</tt> thread when <a href="qapplication.html">QApplication</a> is destroyed, regardless of whether or not the <tt>main()</tt> thread has actually finished.</li>
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<p><b>See also </b><a href="qthread.html">QThread</a>.</p>
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<div class="func">
<h2>Member Function Documentation</h2>
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<h3 class="fn"><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"><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"><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 true 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 setLocalData or localData.</p>
<p><b>See also </b><a href="qthreadstorage.html#localData">localData</a>().</p>
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<h3 class="fn"><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"><a name="localData-2"></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"><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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