Sometimes with QThread you see something like this:
void run() { while (true) { { QMutexLocker lock(&mMutexData); if (mQuit) break; } msleep (200); } mWaitExit.wakeAll(); } void stop() { mMutexData.lock(); mQuit = true; mMutexData.unlock(); mWaitExit.wait(&mMutexExit); }
This is potentially problematic. Why? Consider the extreme case of a function shutdown() which does something like this:
void shutdown() { thread->stop(); delete thread; }
Congratulations, you’ve just introduced a race condition. Why, you will ask? You’re waiting for the thread to end before deleting it, right?
No. And this has to do with the way Qt implements QThread::wait() which you should have probably used in the first place, if you really need this sort of functionality.
Qt hooks a pthread cleanup handler in the native thread which will call wakeAll() on a QWaitCondition stored inside the pimpl of QThread. And this pimpl – you might have guessed – is gone when you call delete.
