如果从同一信号调用Qt，Qt可以同时调用两个插槽吗？

Question

If there are two slots in two different threads and these slots are connected to a signal in a third thread. Can it happen, that both slots get called at the same time by the signal or do they get called synchronized every time?

I ask because i want to send some callback data structure (encapsulated with QSharedPointer ) and ask if locking mechanism inside is needed.

Answer 1

You don't need to lock the actual signal/slot calls if you're using a Qt::QueuedConnection to pass the information to your threads, as the QueuedConnection mechanism handles this in a thread-safe manner.

That being said, you still need to protect any shared memory your threads access, regardless of how they were called. The fact that a third thread emitted a single signal to cause both slots to be called will not change this.

Answer 2

Have a look here (official Qt documentation for Qt's signal/slot mechanism regarding threads).

Each slot is called inside its thread, therefore I am pretty sure anything can happen. You should install a lock mechanism.