forever {
    mutex.lock();
    keyPressed.wait(&mutex);
    do_something();
    mutex.unlock();
}

forever {
    getchar();
    keyPressed.wakeAll();
}

forever {
    mutex.lock();
    keyPressed.wait(&mutex);
    ++count;
    mutex.unlock();

    do_something();

    mutex.lock();
    --count;
    mutex.unlock();
}

forever {
    getchar();

    mutex.lock();
    // Sleep until there are no busy worker threads
    while (count > 0) {
        mutex.unlock();
        sleep(1);
        mutex.lock();
    }
    keyPressed.wakeAll();
    mutex.unlock();
}

Member Function Documentation

QWaitCondition::QWaitCondition()

Constructs a new wait condition object.

QWaitCondition::~QWaitCondition()

Destroys the wait condition object.

void QWaitCondition::notify_all()

This function is provided for STL compatibility. It is equivalent to wakeAll().

This function was introduced in Qt 5.8.

void QWaitCondition::notify_one()

This function is provided for STL compatibility. It is equivalent to wakeOne().

This function was introduced in Qt 5.8.

bool QWaitCondition::wait(QMutex *lockedMutex, unsigned long time = ULONG_MAX)

Releases the lockedMutex and waits on the wait condition. The lockedMutex must be initially locked by the calling thread. If lockedMutex is not in a locked state, the behavior is undefined. If lockedMutex is a recursive mutex, this function returns immediately. The lockedMutex will be unlocked, and the calling thread will block until either of these conditions is met:

• Another thread signals it using wakeOne() or wakeAll(). This function will return true in this case.
• time milliseconds has elapsed. If time is 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.

The 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.

See also wakeOne() and wakeAll().

bool QWaitCondition::wait(QReadWriteLock *lockedReadWriteLock, unsigned long time = ULONG_MAX)

Releases the lockedReadWriteLock and waits on the wait condition. The lockedReadWriteLock must be initially locked by the calling thread. If lockedReadWriteLock is not in a locked state, this function returns immediately. The lockedReadWriteLock must not be locked recursively, otherwise this function will not release the lock properly. The lockedReadWriteLock will be unlocked, and the calling thread will block until either of these conditions is met:

• Another thread signals it using wakeOne() or wakeAll(). This function will return true in this case.
• time milliseconds has elapsed. If time is 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.

The 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.

This function was introduced in Qt 4.4.

See also wakeOne() and wakeAll().

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.

See also wakeOne().

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.

See also wakeAll().