qwaitcondition_unix.cpp

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#include "qwaitcondition.h"
#include "qmutex.h"
#include <pthread.h>

#define MIN(a,b) ((a)<(b)?(a):(b))

static void report_error(int code, const char *where, const char *what)
{
    if (code != 0)
        qWarning("%s: %s failure: %d", where, what, code);
}

class QWaitConditionPrivate
{
  public:
    pthread_mutex_t mutex;
    pthread_cond_t cond;
    int waiters;
    int wakeups;

    void wait()
    {
        int code;
        for (;;)
        {
            code = pthread_cond_wait(&cond, &mutex);
            if (code == 0 && 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;
        }

        --waiters;
        if (code == 0)
        {
            --wakeups;
        }
        else
        {
            report_error(code, "QWaitCondition::wait()", "cv wait");
        }
        report_error(pthread_mutex_unlock(&mutex), "QWaitCondition::wait()", "mutex unlock");
    }
};


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;
}


QWaitCondition::~QWaitCondition()
{
    report_error(pthread_cond_destroy(&d->cond), "QWaitCondition", "cv destroy");
    report_error(pthread_mutex_destroy(&d->mutex), "QWaitCondition", "mutex destroy");
    delete d;
}

void QWaitCondition::wakeOne()
{
    report_error(pthread_mutex_lock(&d->mutex), "QWaitCondition::wakeOne()", "mutex lock");
    d->wakeups = MIN(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");
}

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");
}

void QWaitCondition::wait(QMutex *mutex)
{
    if (!mutex) return;

    report_error(pthread_mutex_lock(&d->mutex), "QWaitCondition::wait()", "mutex lock");
    ++d->waiters;
    mutex->unlock();
    d->wait();
    mutex->lock();
}