/******************************************************************************** Copyright (C) 1992-2006 Trolltech ASA. All rights reserved.**** This file is part of the QtCore module of the Qt Toolkit.**** This file may be used under the terms of the GNU General Public** License version 2.0 as published by the Free Software Foundation** and appearing in the file LICENSE.GPL included in the packaging of** this file.  Please review the following information to ensure GNU** General Public Licensing requirements will be met:** http://www.trolltech.com/products/qt/opensource.html**** If you are unsure which license is appropriate for your use, please** review the following information:** http://www.trolltech.com/products/qt/licensing.html or contact the** sales department at sales@trolltech.com.**** This file is provided AS IS with NO WARRANTY OF ANY KIND, INCLUDING THE** WARRANTY OF DESIGN, MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.******************************************************************************/#include "qplatformdefs.h"#include "qwaitcondition.h"#include "qmutex.h"#include "qatomic.h"#include "qmutex_p.h"#include "qstring.h"#include <errno.h>#ifndef QT_NO_THREADstatic void report_error(int code, const char *where, const char *what){    if (code != 0)        qWarning("%s: %s failure: %s", where, what, qPrintable(qt_error_string(code)));}struct QWaitConditionPrivate {    pthread_mutex_t mutex;    pthread_cond_t cond;    int waiters;    int wakeups;};/*!    \class QWaitCondition    \brief The QWaitCondition class provides a condition variable for    synchronizing threads.    \threadsafe    \ingroup thread    \ingroup environment    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:    \code        forever {            mutex.lock();            keyPressed.wait(&mutex);            do_something();            mutex.unlock();        }    \endcode    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:    \code        forever {            getchar();            keyPressed.wakeAll();        }    \endcode    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:    \code        forever {            mutex.lock();            keyPressed.wait(&mutex);            ++count;            mutex.unlock();            do_something();            mutex.lock();            --count;            mutex.unlock();        }    \endcode    Here's the code for the fourth thread:    \code        forever {            getchar();            mutex.lock();            // Sleep until there are no busy worker threads            while (count > 0) {                mutex.unlock();                sleep(1);                mutex.lock();            }            mutex.unlock();            keyPressed.wakeAll();        }    \endcode    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}*//*!    Constructs a new wait condition object.*/QWaitCondition::QWaitCondition(){    d = new QWaitConditionPrivate;    report_error(pthread_mutex_init(&d->mutex, NULL), "QWaitCondition", "mutex init");    report_error(pthread_cond_init(&d->cond, NULL), "QWaitCondition", "cv init");    d->waiters = d->wakeups = 0;}/*!    Destroys the wait condition object.*/QWaitCondition::~QWaitCondition(){    report_error(pthread_cond_destroy(&d->cond), "QWaitCondition", "cv destroy");    report_error(pthread_mutex_destroy(&d->mutex), "QWaitCondition", "mutex destroy");    delete d;}/*!    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()*/void QWaitCondition::wakeOne(){    report_error(pthread_mutex_lock(&d->mutex), "QWaitCondition::wakeOne()", "mutex lock");    d->wakeups = qMin(d->wakeups + 1, d->waiters);    report_error(pthread_cond_signal(&d->cond), "QWaitCondition::wakeOne()", "cv signal");    report_error(pthread_mutex_unlock(&d->mutex), "QWaitCondition::wakeOne()", "mutex unlock");}/*!    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() */void QWaitCondition::wakeAll(){    report_error(pthread_mutex_lock(&d->mutex), "QWaitCondition::wakeAll()", "mutex lock");    d->wakeups = d->waiters;    report_error(pthread_cond_broadcast(&d->cond), "QWaitCondition::wakeAll()", "cv broadcast");    report_error(pthread_mutex_unlock(&d->mutex), "QWaitCondition::wakeAll()", "mutex unlock");}/*!    Releases the locked \a mutex and wait 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() */bool QWaitCondition::wait(QMutex *mutex, unsigned long time){    if (! mutex)        return false;    if (mutex->d->recursive) {        qWarning("QWaitCondition: cannot wait on recursive mutexes");        return false;    }    report_error(pthread_mutex_lock(&d->mutex), "QWaitCondition::wait()", "mutex lock");    ++d->waiters;    mutex->unlock();    int code;    forever {        if (time != ULONG_MAX) {            struct timeval tv;            gettimeofday(&tv, 0);            timespec ti;            ti.tv_nsec = (tv.tv_usec + (time % 1000) * 1000) * 1000;            ti.tv_sec = tv.tv_sec + (time / 1000) + (ti.tv_nsec / 1000000000);            ti.tv_nsec %= 1000000000;            code = pthread_cond_timedwait(&d->cond, &d->mutex, &ti);        } else {            code = pthread_cond_wait(&d->cond, &d->mutex);        }        if (code == 0 && d->wakeups == 0) {            // many vendors warn of spurios wakeups from            // pthread_cond_wait(), especially after signal delivery,            // even though POSIX doesn't allow for it... sigh            continue;        }        break;    }    Q_ASSERT_X(d->waiters > 0, "QWaitCondition::wait", "internal error (waiters)");    --d->waiters;    if (code == 0) {        Q_ASSERT_X(d->wakeups > 0, "QWaitCondition::wait", "internal error (wakeups)");        --d->wakeups;    }    report_error(pthread_mutex_unlock(&d->mutex), "QWaitCondition::wait()", "mutex unlock");    mutex->lock();    if (code && code != ETIMEDOUT)        report_error(code, "QWaitCondition::wait()", "cv wait");    return (code == 0);}#endif // QT_NO_THREAD