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Diffstat (limited to 'src/corelib/thread/qwaitcondition.qdoc')
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diff --git a/src/corelib/thread/qwaitcondition.qdoc b/src/corelib/thread/qwaitcondition.qdoc new file mode 100644 index 0000000000..8138763f55 --- /dev/null +++ b/src/corelib/thread/qwaitcondition.qdoc @@ -0,0 +1,173 @@ +/**************************************************************************** +** +** Copyright (C) 2011 Nokia Corporation and/or its subsidiary(-ies). +** All rights reserved. +** Contact: Nokia Corporation (qt-info@nokia.com) +** +** This file is part of the documentation of the Qt Toolkit. +** +** $QT_BEGIN_LICENSE:FDL$ +** No Commercial Usage +** This file contains pre-release code and may not be distributed. +** You may use this file in accordance with the terms and conditions +** contained in the Technology Preview License Agreement accompanying +** this package. +** +** GNU Free Documentation License +** Alternatively, this file may be used under the terms of the GNU Free +** Documentation License version 1.3 as published by the Free Software +** Foundation and appearing in the file included in the packaging of this +** file. +** +** If you have questions regarding the use of this file, please contact +** Nokia at qt-info@nokia.com. +** $QT_END_LICENSE$ +** +****************************************************************************/ + +/*! + \class QWaitCondition + \brief The QWaitCondition class provides a condition variable for + synchronizing threads. + + \threadsafe + + \ingroup thread + + QWaitCondition allows a thread to tell other threads that some + sort of condition has been met. One or many threads can block + waiting for a QWaitCondition to set a condition with wakeOne() or + wakeAll(). Use wakeOne() to wake one randomly selected condition or + wakeAll() to wake them all. + + For example, let's suppose that we have three tasks that should + be performed whenever the user presses a key. Each task could be + split into a thread, each of which would have a + \l{QThread::run()}{run()} body like this: + + \snippet doc/src/snippets/code/src_corelib_thread_qwaitcondition_unix.cpp 0 + + Here, the \c keyPressed variable is a global variable of type + QWaitCondition. + + A fourth thread would read key presses and wake the other three + threads up every time it receives one, like this: + + \snippet doc/src/snippets/code/src_corelib_thread_qwaitcondition_unix.cpp 1 + + The order in which the three threads are woken up is undefined. + Also, if some of the threads are still in \c do_something() when + the key is pressed, they won't be woken up (since they're not + waiting on the condition variable) and so the task will not be + performed for that key press. This issue can be solved using a + counter and a QMutex to guard it. For example, here's the new + code for the worker threads: + + \snippet doc/src/snippets/code/src_corelib_thread_qwaitcondition_unix.cpp 2 + + Here's the code for the fourth thread: + + \snippet doc/src/snippets/code/src_corelib_thread_qwaitcondition_unix.cpp 3 + + The mutex is necessary because the results of two threads + attempting to change the value of the same variable + simultaneously are unpredictable. + + Wait conditions are a powerful thread synchronization primitive. + The \l{threads/waitconditions}{Wait Conditions} example shows how + to use QWaitCondition as an alternative to QSemaphore for + controlling access to a circular buffer shared by a producer + thread and a consumer thread. + + \sa QMutex, QSemaphore, QThread, {Wait Conditions Example} +*/ + +/*! + \fn QWaitCondition::QWaitCondition() + + Constructs a new wait condition object. +*/ + +/*! + \fn QWaitCondition::~QWaitCondition() + + Destroys the wait condition object. +*/ + +/*! + \fn void QWaitCondition::wakeOne() + + Wakes one thread waiting on the wait condition. The thread that + is woken up depends on the operating system's scheduling + policies, and cannot be controlled or predicted. + + If you want to wake up a specific thread, the solution is + typically to use different wait conditions and have different + threads wait on different conditions. + + \sa wakeAll() +*/ + +/*! + \fn void QWaitCondition::wakeAll() + + Wakes all threads waiting on the wait condition. The order in + which the threads are woken up depends on the operating system's + scheduling policies and cannot be controlled or predicted. + + \sa wakeOne() +*/ + +/*! + \fn bool QWaitCondition::wait(QMutex *mutex, unsigned long time) + + Releases the locked \a mutex and waits on the wait condition. The + \a mutex must be initially locked by the calling thread. If \a + mutex is not in a locked state, this function returns + immediately. If \a mutex is a recursive mutex, this function + returns immediately. The \a mutex will be unlocked, and the + calling thread will block until either of these conditions is met: + + \list + \o Another thread signals it using wakeOne() or wakeAll(). This + function will return true in this case. + \o \a time milliseconds has elapsed. If \a time is \c ULONG_MAX + (the default), then the wait will never timeout (the event + must be signalled). This function will return false if the + wait timed out. + \endlist + + The mutex will be returned to the same locked state. This + function is provided to allow the atomic transition from the + locked state to the wait state. + + \sa wakeOne(), wakeAll() +*/ + +/*! + \fn bool QWaitCondition::wait(QReadWriteLock *readWriteLock, unsigned long time) + \since 4.4 + + Releases the locked \a readWriteLock and waits on the wait + condition. The \a readWriteLock must be initially locked by the + calling thread. If \a readWriteLock is not in a locked state, this + function returns immediately. The \a readWriteLock must not be + locked recursively, otherwise this function will not release the + lock properly. The \a readWriteLock will be unlocked, and the + calling thread will block until either of these conditions is met: + + \list + \o Another thread signals it using wakeOne() or wakeAll(). This + function will return true in this case. + \o \a time milliseconds has elapsed. If \a time is \c ULONG_MAX + (the default), then the wait will never timeout (the event + must be signalled). This function will return false if the + wait timed out. + \endlist + + The \a readWriteLock will be returned to the same locked + state. This function is provided to allow the atomic transition + from the locked state to the wait state. + + \sa wakeOne(), wakeAll() +*/ |