Reusing QMutex and QWaitCondition

Question

Are QMutex+QWaitCondition objects reusable? I have a method to wait for some threads to complete.

void FinishWait()
{
    mutex.lock();
    waitCondition(&qMutex, ULONG_MAX);
}

The waitCondition.wakeOne() is called on a different Thread.

The first call to FinishWait() works but the the second call doesn't return even if I specify timeout.

score 4 · Accepted Answer · answered Mar 07 '11 at 10:32

4

Assuming "mutex" and "qMutex" mean the same variable (it doesn't make much sense otherwise), you need to unlock the mutex after the wait() returns.

void FinishWait()
{
    mutex.lock();
    waitCondition.wait(&mutex);
    mutex.unlock();
}

answered Mar 07 '11 at 10:32

Gunther Piez

The documentation http://doc.qt.nokia.com/latest/qwaitcondition.html#wait says: "The mutex will be unlocked, and the calling thread will block until either of these conditions is met...." – tvr Mar 07 '11 at 10:57
3

And if you read further I am pretty sure the documentation says something like "If the wait() function exits, the mutex is atomically locked again", because thats the semantics of a wait condition. – Gunther Piez Mar 07 '11 at 11:00

1 Answers1