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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 >QReadLocker</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>
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<h1 class="title">QReadLocker Class</h1>
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<p>The <a href="qreadlocker.html">QReadLocker</a> class is a convenience class that simplifies locking and unlocking read-write locks for read access. <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 <QReadLocker></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="qreadlocker-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="qreadlocker.html#QReadLocker">QReadLocker</a></b>(QReadWriteLock *<i>lock</i>)</td></tr>
<tr><td class="memItemLeft rightAlign topAlign"> </td><td class="memItemRight bottomAlign"><b><a href="qreadlocker.html#dtor.QReadLocker">~QReadLocker</a></b>()</td></tr>
<tr><td class="memItemLeft rightAlign topAlign"> QReadWriteLock *</td><td class="memItemRight bottomAlign"><b><a href="qreadlocker.html#readWriteLock">readWriteLock</a></b>() const</td></tr>
<tr><td class="memItemLeft rightAlign topAlign"> void </td><td class="memItemRight bottomAlign"><b><a href="qreadlocker.html#relock">relock</a></b>()</td></tr>
<tr><td class="memItemLeft rightAlign topAlign"> void </td><td class="memItemRight bottomAlign"><b><a href="qreadlocker.html#unlock">unlock</a></b>()</td></tr>
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<h2 id="details">Detailed Description</h2>
<p>The <a href="qreadlocker.html">QReadLocker</a> class is a convenience class that simplifies locking and unlocking read-write locks for read access.</p>
<p>The purpose of <a href="qreadlocker.html">QReadLocker</a> (and <a href="qwritelocker.html">QWriteLocker</a>) is to simplify <a href="qreadwritelock.html">QReadWriteLock</a> locking and unlocking. Locking and unlocking statements or in exception handling code is error-prone and difficult to debug. <a href="qreadlocker.html">QReadLocker</a> can be used in such situations to ensure that the state of the lock is always well-defined.</p>
<p>Here's an example that uses <a href="qreadlocker.html">QReadLocker</a> to lock and unlock a read-write lock for reading:</p>
<pre class="cpp">
<span class="type"><a href="qreadwritelock.html">QReadWriteLock</a></span> lock;
<span class="type"><a href="qbytearray.html">QByteArray</a></span> readData()
{
<span class="type"><a href="qreadlocker.html#QReadLocker">QReadLocker</a></span> locker(<span class="operator">&</span>lock);
<span class="operator">.</span><span class="operator">.</span><span class="operator">.</span>
<span class="keyword">return</span> data;
}
</pre>
<p>It is equivalent to the following code:</p>
<pre class="cpp">
<span class="type"><a href="qreadwritelock.html">QReadWriteLock</a></span> lock;
<span class="type"><a href="qbytearray.html">QByteArray</a></span> readData()
{
lock<span class="operator">.</span>lockForRead();
<span class="operator">.</span><span class="operator">.</span><span class="operator">.</span>
lock<span class="operator">.</span>unlock();
<span class="keyword">return</span> data;
}
</pre>
<p>The <a href="qmutexlocker.html">QMutexLocker</a> documentation shows examples where the use of a locker object greatly simplifies programming.</p>
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<p><b>See also </b><a href="qwritelocker.html">QWriteLocker</a> and <a href="qreadwritelock.html">QReadWriteLock</a>.</p>
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<h2>Member Function Documentation</h2>
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<h3 class="fn" id="QReadLocker"><a name="QReadLocker"></a>QReadLocker::<span class="name">QReadLocker</span>(<span class="type"><a href="qreadwritelock.html">QReadWriteLock</a></span> *<i>lock</i>)</h3>
<p>Constructs a <a href="qreadlocker.html">QReadLocker</a> and locks <i>lock</i> for reading. The lock will be unlocked when the <a href="qreadlocker.html">QReadLocker</a> is destroyed. If <code>lock</code> is zero, <a href="qreadlocker.html">QReadLocker</a> does nothing.</p>
<p><b>See also </b><a href="qreadwritelock.html#lockForRead">QReadWriteLock::lockForRead</a>().</p>
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<h3 class="fn" id="dtor.QReadLocker"><a name="dtor.QReadLocker"></a>QReadLocker::<span class="name">~QReadLocker</span>()</h3>
<p>Destroys the <a href="qreadlocker.html">QReadLocker</a> and unlocks the lock that was passed to the constructor.</p>
<p><b>See also </b><a href="qreadwritelock.html#unlock">QReadWriteLock::unlock</a>().</p>
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<h3 class="fn" id="readWriteLock"><a name="readWriteLock"></a><span class="type"><a href="qreadwritelock.html">QReadWriteLock</a></span> *QReadLocker::<span class="name">readWriteLock</span>() const</h3>
<p>Returns a pointer to the read-write lock that was passed to the constructor.</p>
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<h3 class="fn" id="relock"><a name="relock"></a><span class="type">void</span> QReadLocker::<span class="name">relock</span>()</h3>
<p>Relocks an unlocked lock.</p>
<p><b>See also </b><a href="qreadlocker.html#unlock">unlock</a>().</p>
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<h3 class="fn" id="unlock"><a name="unlock"></a><span class="type">void</span> QReadLocker::<span class="name">unlock</span>()</h3>
<p>Unlocks the lock associated with this locker.</p>
<p><b>See also </b><a href="qreadwritelock.html#unlock">QReadWriteLock::unlock</a>().</p>
<!-- @@@unlock -->
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