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196 lines
7.2 KiB
196 lines
7.2 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:333 -->
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<html>
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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>QMutex 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:link { color: #004faf; text-decoration: none }
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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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</head>
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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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| <a href="annotated.html">
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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>QMutex Class Reference</h1>
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<p>The QMutex class provides access serialization between threads.
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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="qmutex-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="#QMutex"><b>QMutex</b></a> ( bool recursive = FALSE )</li>
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<li class=fn>virtual <a href="#~QMutex"><b>~QMutex</b></a> ()</li>
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<li class=fn>void <a href="#lock"><b>lock</b></a> ()</li>
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<li class=fn>void <a href="#unlock"><b>unlock</b></a> ()</li>
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<li class=fn>bool <a href="#locked"><b>locked</b></a> ()</li>
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<li class=fn>bool <a href="#tryLock"><b>tryLock</b></a> ()</li>
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</ul>
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<hr><a name="details"></a><h2>Detailed Description</h2>
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The QMutex class provides access serialization between threads.
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<p>
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<p> The purpose of a QMutex is to protect an object, data structure or
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section of code so that only one thread can access it at a time
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(This is similar to the Java <tt>synchronized</tt> keyword). For
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example, say there is a method which prints a message to the user
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on two lines:
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<p> <pre>
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int number = 6;
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void method1()
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{
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number *= 5;
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number /= 4;
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}
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void method2()
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{
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number *= 3;
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number /= 2;
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}
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</pre>
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<p> If these two methods are called in succession, the following happens:
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<p> <pre>
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// method1()
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number *= 5; // number is now 30
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number /= 4; // number is now 7
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// method2()
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number *= 3; // nubmer is now 21
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number /= 2; // number is now 10
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</pre>
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<p> If these two methods are called simultaneously from two threads then the
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following sequence could result:
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<p> <pre>
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// Thread 1 calls method1()
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number *= 5; // number is now 30
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// Thread 2 calls method2().
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//
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// Most likely Thread 1 has been put to sleep by the operating
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// system to allow Thread 2 to run.
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number *= 3; // number is now 90
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number /= 2; // number is now 45
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// Thread 1 finishes executing.
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number /= 4; // number is now 11, instead of 10
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</pre>
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<p> If we add a mutex, we should get the result we want:
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<p> <pre>
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QMutex mutex;
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int number = 6;
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void method1()
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{
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mutex.<a href="#lock">lock</a>();
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number *= 5;
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number /= 4;
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mutex.<a href="#unlock">unlock</a>();
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}
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void method2()
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{
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mutex.<a href="#lock">lock</a>();
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number *= 3;
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number /= 2;
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mutex.<a href="#unlock">unlock</a>();
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}
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</pre>
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<p> Then only one thread can modify <tt>number</tt> at any given time and
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the result is correct. This is a trivial example, of course, but
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applies to any other case where things need to happen in a
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particular sequence.
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<p> When you call <a href="#lock">lock</a>() in a thread, other threads that try to call
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lock() in the same place will block until the thread that got the
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lock calls <a href="#unlock">unlock</a>(). A non-blocking alternative to lock() is
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<a href="#tryLock">tryLock</a>().
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<p>See also <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="QMutex"></a>QMutex::QMutex ( bool recursive = FALSE )
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</h3>
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Constructs a new mutex. The mutex is created in an unlocked state.
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A recursive mutex is created if <em>recursive</em> is TRUE; a normal
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mutex is created if <em>recursive</em> is FALSE (the default). With a
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recursive mutex, a thread can lock the same mutex multiple times
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and it will not be unlocked until a corresponding number of
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<a href="#unlock">unlock</a>() calls have been made.
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<h3 class=fn><a name="~QMutex"></a>QMutex::~QMutex ()<tt> [virtual]</tt>
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</h3>
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Destroys the mutex.
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<p> <b>Warning:</b> If you destroy a mutex that still holds a lock the
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resultant behavior is undefined.
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<h3 class=fn>void <a name="lock"></a>QMutex::lock ()
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</h3>
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Attempt to lock the mutex. If another thread has locked the mutex
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then this call will <em>block</em> until that thread has unlocked it.
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<p> <p>See also <a href="#unlock">unlock</a>() and <a href="#locked">locked</a>().
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<h3 class=fn>bool <a name="locked"></a>QMutex::locked ()
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</h3>
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Returns TRUE if the mutex is locked by another thread; otherwise
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returns FALSE.
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<p> <b>Warning:</b> Due to differing implementations of recursive mutexes on
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various platforms, calling this function from the same thread that
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previously locked the mutex will return undefined results.
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<p> <p>See also <a href="#lock">lock</a>() and <a href="#unlock">unlock</a>().
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<h3 class=fn>bool <a name="tryLock"></a>QMutex::tryLock ()
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</h3>
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Attempt to lock the mutex. If the lock was obtained, this function
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returns TRUE. If another thread has locked the mutex, this
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function returns FALSE, instead of waiting for the mutex to become
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available, i.e. it does not block.
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<p> If the lock was obtained, the mutex must be unlocked with <a href="#unlock">unlock</a>()
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before another thread can successfully lock it.
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<p> <p>See also <a href="#lock">lock</a>(), <a href="#unlock">unlock</a>(), and <a href="#locked">locked</a>().
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<h3 class=fn>void <a name="unlock"></a>QMutex::unlock ()
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</h3>
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Unlocks the mutex. Attempting to unlock a mutex in a different
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thread to the one that locked it results in an error. Unlocking a
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mutex that is not locked results in undefined behaviour (varies
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between different Operating Systems' thread implementations).
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<p> <p>See also <a href="#lock">lock</a>() and <a href="#locked">locked</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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