Mastering Qt 5

Flying over Qt multithreading technologies

Built upon QThread, several threading technologies are available in Qt. First, to synchronize threads, the usual approach is to use a mutual exclusion (mutex) to have a mutual exclusion for a given resource. Qt provides it by means of the QMutex class. Its usage is straightforward:

QMutex mutex; 
int number = 1; 
 
mutex.lock(); 
number *= 2; 
mutex.unlock(); 

From the mutex.lock() instruction, any other thread trying to lock the mutex will wait until mutex.unlock() has been called.

The locking/unlocking mechanism is error-prone in complex code. You can easily forget to unlock a mutex in a specific exit condition, causing a deadlock. To simplify this situation, Qt provides a QMutexLocker that should be used where ...