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221 lines
7.3 KiB
221 lines
7.3 KiB
14 years ago
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
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<!-- /home/espenr/tmp/qt-3.3.8-espenr-2499/qt-x11-free-3.3.8/src/tools/qmutex_unix.cpp:511 -->
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
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<title>QMutexLocker Class</title>
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<style type="text/css"><!--
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fn { margin-left: 1cm; text-indent: -1cm; }
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a:visited { color: #672967; text-decoration: none }
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body { background: #ffffff; color: black; }
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--></style>
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<body>
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<table border="0" cellpadding="0" cellspacing="0" width="100%">
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<tr bgcolor="#E5E5E5">
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<td valign=center>
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<a href="index.html">
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<font color="#004faf">Home</font></a>
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| <a href="classes.html">
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<font color="#004faf">All Classes</font></a>
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| <a href="mainclasses.html">
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<font color="#004faf">Main Classes</font></a>
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<font color="#004faf">Annotated</font></a>
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<font color="#004faf">Grouped Classes</font></a>
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<font color="#004faf">Functions</font></a>
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</td>
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<td align="right" valign="center"><img src="logo32.png" align="right" width="64" height="32" border="0"></td></tr></table><h1 align=center>QMutexLocker Class Reference</h1>
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<p>The QMutexLocker class simplifies locking and unlocking QMutexes.
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<a href="#details">More...</a>
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<p>All the functions in this class are <a href="threads.html#threadsafe">thread-safe</a> when Qt is built with thread support.</p>
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<p><tt>#include <<a href="qmutex-h.html">qmutex.h</a>></tt>
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<p><a href="qmutexlocker-members.html">List of all member functions.</a>
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<h2>Public Members</h2>
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<ul>
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<li class=fn><a href="#QMutexLocker"><b>QMutexLocker</b></a> ( QMutex * mutex )</li>
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<li class=fn><a href="#~QMutexLocker"><b>~QMutexLocker</b></a> ()</li>
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<li class=fn>QMutex * <a href="#mutex"><b>mutex</b></a> () const</li>
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</ul>
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<hr><a name="details"></a><h2>Detailed Description</h2>
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The QMutexLocker class simplifies locking and unlocking QMutexes.
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<p>
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<p>
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<p> The purpose of QMutexLocker is to simplify <a href="qmutex.html">QMutex</a> locking and
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unlocking. Locking and unlocking a QMutex in complex functions and
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statements or in exception handling code is error prone and
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difficult to debug. QMutexLocker should be used in such situations
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to ensure that the state of the mutex is well defined and always
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locked and unlocked properly.
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<p> QMutexLocker should be created within a function where a QMutex
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needs to be locked. The mutex is locked when QMutexLocker is
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created, and unlocked when QMutexLocker is destroyed.
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<p> For example, this complex function locks a QMutex upon entering
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the function and unlocks the mutex at all the exit points:
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<p> <pre>
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int complexFunction( int flag )
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{
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mutex.lock();
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int return_value = 0;
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switch ( flag ) {
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case 0:
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case 1:
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{
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mutex.unlock();
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return moreComplexFunction( flag );
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}
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case 2:
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{
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int status = anotherFunction();
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if ( status < 0 ) {
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mutex.unlock();
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return -2;
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}
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return_value = status + flag;
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break;
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}
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default:
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{
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if ( flag > 10 ) {
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mutex.unlock();
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return -1;
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}
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break;
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}
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}
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mutex.unlock();
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return return_value;
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}
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</pre>
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<p> This example function will get more complicated as it is
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developed, which increases the likelihood that errors will occur.
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<p> Using QMutexLocker greatly simplifies the code, and makes it more
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readable:
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<p> <pre>
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int complexFunction( int flag )
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{
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QMutexLocker locker( &mutex );
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int return_value = 0;
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switch ( flag ) {
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case 0:
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case 1:
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{
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return moreComplexFunction( flag );
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}
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case 2:
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{
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int status = anotherFunction();
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if ( status < 0 )
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return -2;
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return_value = status + flag;
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break;
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}
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default:
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{
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if ( flag > 10 )
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return -1;
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break;
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}
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}
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return return_value;
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}
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</pre>
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<p> Now, the mutex will always be unlocked when the QMutexLocker
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object is destroyed (when the function returns since <tt>locker</tt> is
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an auto variable). Note that the mutex will be unlocked after
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the call to moreComplexFunction() in this example, avoiding
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possible bugs caused by unlocking the mutex too early, as in
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the first example.
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<p> The same principle applies to code that throws and catches
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exceptions. An exception that is not caught in the function that
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has locked the mutex has no way of unlocking the mutex before the
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exception is passed up the stack to the calling function.
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<p> QMutexLocker also provides a <a href="#mutex">mutex</a>() member function that returns
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the mutex on which the QMutexLocker is operating. This is useful
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for code that needs access to the mutex, such as
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<a href="qwaitcondition.html#wait">QWaitCondition::wait</a>(). For example:
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<p> <pre>
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class SignalWaiter
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{
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private:
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QMutexLocker locker;
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public:
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SignalWaiter( <a href="qmutex.html">QMutex</a> *mutex )
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: locker( mutex )
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{
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}
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void waitForSignal()
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{
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...
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...
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...
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while ( ! signalled )
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waitcondition.wait( locker.<a href="#mutex">mutex</a>() );
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...
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...
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...
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}
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};
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</pre>
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<p> <p>See also <a href="qmutex.html">QMutex</a>, <a href="qwaitcondition.html">QWaitCondition</a>, <a href="environment.html">Environment Classes</a>, and <a href="thread.html">Threading</a>.
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<hr><h2>Member Function Documentation</h2>
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<h3 class=fn><a name="QMutexLocker"></a>QMutexLocker::QMutexLocker ( <a href="qmutex.html">QMutex</a> * mutex )
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</h3>
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<p> Constructs a QMutexLocker and locks <em>mutex</em>. The mutex will be
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unlocked when the QMutexLocker is destroyed. If <em>mutex</em> is zero,
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QMutexLocker does nothing.
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<p> <p>See also <a href="qmutex.html#lock">QMutex::lock</a>().
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<h3 class=fn><a name="~QMutexLocker"></a>QMutexLocker::~QMutexLocker ()
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</h3>
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<p> Destroys the QMutexLocker and unlocks the mutex which was locked
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in the constructor.
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<p> <p>See also <a href="#QMutexLocker">QMutexLocker::QMutexLocker</a>() and <a href="qmutex.html#unlock">QMutex::unlock</a>().
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<h3 class=fn><a href="qmutex.html">QMutex</a> * <a name="mutex"></a>QMutexLocker::mutex () const
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</h3>
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<p> Returns a pointer to the mutex which was locked in the
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constructor.
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<p> <p>See also <a href="#QMutexLocker">QMutexLocker::QMutexLocker</a>().
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<!-- eof -->
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<hr><p>
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This file is part of the <a href="index.html">Qt toolkit</a>.
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Copyright © 1995-2007
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<a href="http://www.trolltech.com/">Trolltech</a>. All Rights Reserved.<p><address><hr><div align=center>
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<table width=100% cellspacing=0 border=0><tr>
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<td>Copyright © 2007
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<a href="troll.html">Trolltech</a><td align=center><a href="trademarks.html">Trademarks</a>
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<td align=right><div align=right>Qt 3.3.8</div>
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</table></div></address></body>
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</html>
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