Multithreading problem

[y.shan]

Hi, my current situation is this:

I'm using threads in my application and i want to communicate with the main thread.
At the moment I'm doing it like this:

thread:

[...]
extern QMutex waitForUserLock;
extern QWaitCondition waitForUser;
[...]
text = [...];
customEvent * send_event = new customEvent(type);
send_event->setData((void*)text);
 
waitForUserLock.lock();
QApplication::postEvent((QObject*)mainwindow, send_event);
waitForUser.wait(&waitForUserLock); //sometimes hangs here
waitForUserLock.unlock();
[...]

[...]
extern QMutex waitForUserLock;
extern QWaitCondition waitForUser;
[...]
text = [...];
customEvent * send_event = new customEvent(type);
send_event->setData((void*)text);

waitForUserLock.lock();
QApplication::postEvent((QObject*)mainwindow, send_event);
waitForUser.wait(&waitForUserLock); //sometimes hangs here
waitForUserLock.unlock();
[...]

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mainwindow:

[...]
QMutex waitForUserLock;
QWaitCondition waitForUser;
[...]
void mainwindow::customEvent(QEvent *e)
{
    customEvent *me = (customEvent *) e;
    switch (me->type())
    {
    case type:
        waitForUserLock.lock();
        my_function((char*)me->data());
        waitForUser.wakeOne();
        waitForUserLock.unlock();
        return;
    [...]
    }
}
[...]

[...]
QMutex waitForUserLock;
QWaitCondition waitForUser;
[...]
void mainwindow::customEvent(QEvent *e)
{
    customEvent *me = (customEvent *) e;
    switch (me->type())
    {
    case type:
        waitForUserLock.lock();
        my_function((char*)me->data());
        waitForUser.wakeOne();
        waitForUserLock.unlock();
        return;
    [...]
    }
}
[...]

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The problem is the wait, where the application sometimes hangs.
Does anyone know where the mistake is or is there a better solution?

[DeepDiver]

you can use signals and slots for cross thread communication.
Meaning: you emit a signal in one thread and catch it in a slot in the main thread.

Good luck,

Tom

[high_flyer]

From the code you posted its hard to tell.
It sounds like you are having a dead lock
Two things:
1. Don't use gloabl mutexes, and remember, you should mutex data /resources , not code.
2. Try using tryLock().

[y.shan]

you can use signals and slots for cross thread communication.
Meaning: you emit a signal in one thread and catch it in a slot in the main thread.

Good luck,

Tom

yeah, but isn't this the same as using events?

[high_flyer]

yeah, but isn't this the same as using events?

Yes it is, its what Qt4 does in the background with the signals.