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198 lines
8.4 KiB
198 lines
8.4 KiB
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<!-- /home/espenr/tmp/qt-3.3.8-espenr-2499/qt-x11-free-3.3.8/src/tools/qwaitcondition_unix.cpp:57 -->
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<title>TQWaitCondition Class</title>
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<a href="index.html">
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<font color="#004faf">Home</font></a>
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<font color="#004faf">All Classes</font></a>
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<font color="#004faf">Functions</font></a>
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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>TQWaitCondition Class Reference</h1>
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<p>The TQWaitCondition class allows waiting/waking for conditions 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 TQt is built with thread support.</p>
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<p><tt>#include <<a href="qwaitcondition-h.html">ntqwaitcondition.h</a>></tt>
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<p><a href="qwaitcondition-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="#TQWaitCondition"><b>TQWaitCondition</b></a> ()</li>
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<li class=fn>virtual <a href="#~TQWaitCondition"><b>~TQWaitCondition</b></a> ()</li>
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<li class=fn>bool <a href="#wait"><b>wait</b></a> ( unsigned long time = ULONG_MAX )</li>
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<li class=fn>bool <a href="#wait-2"><b>wait</b></a> ( TQMutex * mutex, unsigned long time = ULONG_MAX )</li>
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<li class=fn>void <a href="#wakeOne"><b>wakeOne</b></a> ()</li>
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<li class=fn>void <a href="#wakeAll"><b>wakeAll</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 TQWaitCondition class allows waiting/waking for conditions between threads.
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<p>
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<p> TQWaitConditions allow a thread to tell other threads that some
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sort of condition has been met; one or many threads can block
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waiting for a TQWaitCondition to set a condition with <a href="#wakeOne">wakeOne</a>() or
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<a href="#wakeAll">wakeAll</a>(). Use wakeOne() to wake one randomly selected event or
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wakeAll() to wake them all. For example, say we have three tasks
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that should be performed every time the user presses a key; each
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task could be split into a thread, each of which would have a
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run() body like this:
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<p> <pre>
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TQWaitCondition key_pressed;
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for (;;) {
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key_pressed.<a href="#wait">wait</a>(); // This is a TQWaitCondition global variable
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// Key was pressed, do something interesting
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do_something();
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}
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</pre>
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<p> A fourth thread would read key presses and wake the other three
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threads up every time it receives one, like this:
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<p> <pre>
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TQWaitCondition key_pressed;
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for (;;) {
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getchar();
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// Causes any thread in key_pressed.<a href="#wait">wait</a>() to return from
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// that method and continue processing
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key_pressed.<a href="#wakeAll">wakeAll</a>();
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}
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</pre>
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<p> Note that the order the three threads are woken up in is
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undefined, and that if some or all of the threads are still in
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do_something() when the key is pressed, they won't be woken up
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(since they're not waiting on the condition variable) and so the
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task will not be performed for that key press. This can be
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avoided by, for example, doing something like this:
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<p> <pre>
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<a href="ntqmutex.html">TQMutex</a> mymutex;
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TQWaitCondition key_pressed;
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int mycount=0;
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// Worker thread code
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for (;;) {
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key_pressed.<a href="#wait">wait</a>(); // This is a TQWaitCondition global variable
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mymutex.<a href="ntqmutex.html#lock">lock</a>();
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mycount++;
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mymutex.<a href="ntqmutex.html#unlock">unlock</a>();
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do_something();
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mymutex.<a href="ntqmutex.html#lock">lock</a>();
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mycount--;
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mymutex.<a href="ntqmutex.html#unlock">unlock</a>();
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}
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// Key reading thread code
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for (;;) {
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getchar();
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mymutex.<a href="ntqmutex.html#lock">lock</a>();
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// Sleep until there are no busy worker threads
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while( mycount > 0 ) {
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mymutex.<a href="ntqmutex.html#unlock">unlock</a>();
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sleep( 1 );
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mymutex.<a href="ntqmutex.html#lock">lock</a>();
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}
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mymutex.<a href="ntqmutex.html#unlock">unlock</a>();
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key_pressed.<a href="#wakeAll">wakeAll</a>();
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}
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</pre>
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<p> The mutexes are necessary because the results of two threads
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attempting to change the value of the same variable simultaneously
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are unpredictable.
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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="TQWaitCondition"></a>TQWaitCondition::TQWaitCondition ()
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</h3>
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Constructs a new event signalling, i.e. wait condition, object.
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<h3 class=fn><a name="~TQWaitCondition"></a>TQWaitCondition::~TQWaitCondition ()<tt> [virtual]</tt>
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</h3>
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Deletes the event signalling, i.e. wait condition, object.
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<h3 class=fn>bool <a name="wait"></a>TQWaitCondition::wait ( unsigned long time = ULONG_MAX )
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</h3>
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Wait on the thread event object. The thread calling this will
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block until either of these conditions is met:
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<ul>
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<li> Another thread signals it using <a href="#wakeOne">wakeOne</a>() or <a href="#wakeAll">wakeAll</a>(). This
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function will return TRUE in this case.
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<li> <em>time</em> milliseconds has elapsed. If <em>time</em> is ULONG_MAX (the
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default), then the wait will never timeout (the event must be
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signalled). This function will return FALSE if the wait timed
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out.
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</ul>
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<p> <p>See also <a href="#wakeOne">wakeOne</a>() and <a href="#wakeAll">wakeAll</a>().
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<h3 class=fn>bool <a name="wait-2"></a>TQWaitCondition::wait ( <a href="ntqmutex.html">TQMutex</a> * mutex, unsigned long time = ULONG_MAX )
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</h3>
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This is an overloaded member function, provided for convenience. It behaves essentially like the above function.
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<p> Release the locked <em>mutex</em> and wait on the thread event object.
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The <em>mutex</em> must be initially locked by the calling thread. If <em>mutex</em> is not in a locked state, this function returns immediately.
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If <em>mutex</em> is a recursive mutex, this function returns
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immediately. The <em>mutex</em> will be unlocked, and the calling thread
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will block until either of these conditions is met:
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<ul>
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<li> Another thread signals it using <a href="#wakeOne">wakeOne</a>() or <a href="#wakeAll">wakeAll</a>(). This
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function will return TRUE in this case.
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<li> <em>time</em> milliseconds has elapsed. If <em>time</em> is ULONG_MAX (the
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default), then the wait will never timeout (the event must be
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signalled). This function will return FALSE if the wait timed
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out.
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</ul>
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<p> The mutex will be returned to the same locked state. This function
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is provided to allow the atomic transition from the locked state
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to the wait state.
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<p> <p>See also <a href="#wakeOne">wakeOne</a>() and <a href="#wakeAll">wakeAll</a>().
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<h3 class=fn>void <a name="wakeAll"></a>TQWaitCondition::wakeAll ()
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</h3>
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This wakes all threads waiting on the TQWaitCondition. The order in
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which the threads are woken up depends on the operating system's
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scheduling policies, and cannot be controlled or predicted.
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<p> <p>See also <a href="#wakeOne">wakeOne</a>().
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<h3 class=fn>void <a name="wakeOne"></a>TQWaitCondition::wakeOne ()
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</h3>
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This wakes one thread waiting on the TQWaitCondition. The thread
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that is woken up depends on the operating system's scheduling
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policies, and cannot be controlled or predicted.
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<p> <p>See also <a href="#wakeAll">wakeAll</a>().
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<hr><p>
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This file is part of the <a href="index.html">TQt 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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<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>TQt 3.3.8</div>
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