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qtsignals-slots

Wait for a SLOT to finish the execution with Qt

In my code I emit a signal mySignal and I want to wait for the end of a connected slot mySlot execution before it continues:

emit mySignal();
// Wait for the end of mySlot execution...

// Some code that has to be executed only after the end of mySlot execution...

Is there a way to do so ?

Solution

  • If the sender and the receiver are in the same thread use Qt::DirectConnection, if they are in 2 different threads use Qt::BlockingQueuedConnection.

    ClassA a;
ClassB b;
ClassC c;
c.moveToThread(aThread);
QObject::connect(&a, &ClassA::signal, &b, &ClassB::slot, Qt::DirectConnection);
QObject::connect(&a, &ClassA::signal, &c, &ClassC::slot, Qt::BlockingQueuedConnection);

    Please note that you will have to disconnect/reconnect if:

    • the sender and the receiver end up the the same thread and they previously were not,or you will have a dead lock.
    • the sender or the receiver end up in 2 different threads and they previously were in the same thread.

    Also Qt::DirectConnection is the default if the sender and receiver are in the same thread (see Qt::AutoConnection).