text: /****************************************************************************
  **
  ** Copyright (C) 2016 The Qt Company Ltd.
  ** Contact: https://www.qt.io/licensing/
  **
  ** This file is part of the documentation of the Qt Toolkit.
  **
  ** $QT_BEGIN_LICENSE:FDL$
  ** Commercial License Usage
  ** Licensees holding valid commercial Qt licenses may use this file in
  ** accordance with the commercial license agreement provided with the
  ** Software or, alternatively, in accordance with the terms contained in
  ** a written agreement between you and The Qt Company. For licensing terms
  ** and conditions see https://www.qt.io/terms-conditions. For further
  ** information use the contact form at https://www.qt.io/contact-us.
  **
  ** GNU Free Documentation License Usage
  ** 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. Please review the following information to ensure
  ** the GNU Free Documentation License version 1.3 requirements
  ** will be met: https://www.gnu.org/licenses/fdl-1.3.html.
  ** $QT_END_LICENSE$
  **
  ****************************************************************************/
  
  /*!
      \class QWaitCondition
      \inmodule QtCore
      \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 thread 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 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 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 code/src_corelib_thread_qwaitcondition_unix.cpp 2
  
      Here's the code for the fourth thread:
  
      \snippet 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{Wait Conditions Example} 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 *lockedMutex, unsigned long time)
      \overload
  */
  /*!
      \fn bool QWaitCondition::wait(QReadWriteLock *lockedReadWriteLock, unsigned long time)
      \overload
  */
  
  /*!
      \fn bool QWaitCondition::wait(QMutex *lockedMutex, QDeadlineTimer deadline)
      \since 5.12
  
      Releases the \a lockedMutex and waits on the wait condition. The
      \a lockedMutex must be initially locked by the calling thread. If \a
      lockedMutex is not in a locked state, the behavior is undefined. If
      \a lockedMutex is a recursive mutex, this function
      returns immediately. The \a lockedMutex will be unlocked, and the
      calling thread will block until either of these conditions is met:
  
      \list
      \li Another thread signals it using wakeOne() or wakeAll(). This
         function will return true in this case.
      \li the deadline given by \a deadline is reached. If \a deadline is
         \c QDeadlineTimer::Forever (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 lockedMutex 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 *lockedReadWriteLock, QDeadlineTimer deadline)
      \since 5.12
  
      Releases the \a lockedReadWriteLock and waits on the wait
      condition.  The \a lockedReadWriteLock must be initially locked by the
      calling thread. If \a lockedReadWriteLock is not in a locked state, this
      function returns immediately. The \a lockedReadWriteLock must not be
      locked recursively, otherwise this function will not release the
      lock properly. The \a lockedReadWriteLock will be unlocked, and the
      calling thread will block until either of these conditions is met:
  
      \list
      \li Another thread signals it using wakeOne() or wakeAll(). This
         function will return true in this case.
      \li the deadline given by \a deadline is reached. If \a deadline is
         \c QDeadlineTimer::Forever (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 lockedReadWriteLock 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 void QWaitCondition::notify_one()
      \since 5.8
  
      This function is provided for STL compatibility. It is equivalent
      to wakeOne().
  */
  
  /*! \fn void QWaitCondition::notify_all()
      \since 5.8
  
      This function is provided for STL compatibility. It is equivalent
      to wakeAll().
  */
  