what can I use to replace sleep and usleep in my Qt app?

Question

I'm importing a portion of existing code into my Qt app and noticed a sleep function in there. I see that this type of function has no place in event programming. What should I do instead?

UPDATE: After thought and feedback I would say the answer is: call sleep outside the GUI main thread only and if you need to wait in the GUI thread use processEvents() or an event loop, this will prevent the GUI from freezing.

Answer 1

It isn't pretty but I found this in the Qt mailing list archives:

The sleep method of QThread is protected, but you can expose it like so:

class SleeperThread : public QThread
{
public:
    static void msleep(unsigned long msecs)
    {
        QThread::msleep(msecs);
    }
};

Then just call:

SleeperThread::msleep(1000);

from any thread.

However, a more elegant solution would be to refactor your code to use a QTimer - this might require you saving the state so you know what to do when the timer goes off.

Answer 2

It is not necessary to break down the events at all. All I needed to do was to call QApplication::processEvents() where sleep() was and this prevents the GUI from freezing.

Answer 3

I don't recommend sleep in a event based system but if you want to ...
You can use a waitcondition, that way you can always interrupt the sleep if neccesary.

//...
QMutex dummy;
dummy.lock();
QWaitCondition waitCondition;
waitCondition.wait(&dummy, waitTime);
//...

Answer 4

The reason why sleep is a bad idea in event based programming is because event based programming is effectively a form on non-preemptive multitasking. By calling sleep, you prevent any other event becoming active and therefore blocking the processing of the thread.

In a request response scenario for udp packets, send the request and immediately wait for the response. Qt has good socket APIs which will ensure that the socket does not block while waiting for the event. The event will come when it comes. In your case the QSocket::readReady signal is your friend.

If you want to schedule an event for some point of time in the future, use QTimer. This will ensure that other events are not blocked.