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  4. [solved] Qt Signal/Slots in one class but emitted from different threads
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[solved] Qt Signal/Slots in one class but emitted from different threads

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  • B Offline
    B Offline
    bazz-dee
    wrote on last edited by
    #1

    Hi,

    i saw a lot of post concerning this topic, but all topics did not match my problem.

    The project is devided in two parts, a library where all processing is done and the GUI. The library is completly in C++/MFC and should not be changed that much because it is also used in none Qt projects which have to be running without Qt dependencies. The library defines an interface to make calls to an GUI. So the Qt GUI also implements this interface in order to receive the calls from the library. The library runs several threads.

    Some of the processing of the GUI calls should not block the library from running. So the GUI class defines slots and signals, the signals are emitted in the implemented interface functions. The signals and slots are connected using:

    @"connect(this, SIGNAL(xyz), this SLOT(xyz));"@

    I think the problem is that the intface functions that emit the signals are running in thread a but the GUI runs in thread b. The right way would be create QObjects inside the library and define the signals on that side, but this is not possible in my case. Any suggestions?

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    • G Offline
      G Offline
      giesbert
      wrote on last edited by
      #2

      You could go a bit another way:

      use

      @
      QMetaObject::invokeMethod(this, "foo", Qt::QueuedConnection);
      @

      There you can also post parameters

      @
      QMetaObject::invokeMethod(this, "foo", Qt::BlockingQueuedConnection, Q_ARG(<param type>, param));
      @

      Nokia Certified Qt Specialist.
      Programming Is Like Sex: One mistake and you have to support it for the rest of your life. (Michael Sinz)

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      • K Offline
        K Offline
        koahnig
        wrote on last edited by
        #3

        The connection is using pointers to the same instance, isn't it?
        I assume that you are using the same object through pointers in different threads. Then this might be possible. However, the signal-slot mimic will more or less generate a direct function call which will be executed in the thread you are emitting the signal. I do not see a way to tell the thread that it has to execute the function in another thread.
        I guess you need to separate the different tasks in two objects. Otherwise it will not function.

        Vote the answer(s) that helped you to solve your issue(s)

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        • A Offline
          A Offline
          andre
          wrote on last edited by
          #4

          You can also use the connection type in your connect statement, if you need.

          It depends on what you want to do in response to those signals though. You can not trigger anything that modifies the GUI from another tread than the GUI thread. That can only be done using queued connections, never with direct method calls or direct connections (amount to pretty much the same thing).

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          • B Offline
            B Offline
            bazz-dee
            wrote on last edited by
            #5

            [quote author="Gerolf" date="1304063870"]You could go a bit another way:

            use

            @
            QMetaObject::invokeMethod(this, "foo", Qt::QueuedConnection);
            @

            There you can also post parameters

            @
            QMetaObject::invokeMethod(this, "foo", Qt::BlockingQueuedConnection, Q_ARG(<param type>, param));
            @
            [/quote]

            That is working, thank you.

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            • G Offline
              G Offline
              giesbert
              wrote on last edited by
              #6

              Using the typed connect also works with emit signal then:

              @
              "connect(this, SIGNAL(xyz), this SLOT(xyz), Qt::QueuedConnection);"
              @

              Nokia Certified Qt Specialist.
              Programming Is Like Sex: One mistake and you have to support it for the rest of your life. (Michael Sinz)

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              • B Offline
                B Offline
                bazz-dee
                wrote on last edited by
                #7

                [quote author="Gerolf" date="1304064590"]Using the typed connect also works with emit signal then:

                @
                "connect(this, SIGNAL(xyz), this SLOT(xyz), Qt::QueuedConnection);"
                @[/quote]

                I tried that before and had no success

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                • G Offline
                  G Offline
                  giesbert
                  wrote on last edited by
                  #8

                  If you then emit inside your class, it did not work? strange... should do logically the same as QMetaObject::invokeMethod

                  Nokia Certified Qt Specialist.
                  Programming Is Like Sex: One mistake and you have to support it for the rest of your life. (Michael Sinz)

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                  • B Offline
                    B Offline
                    bazz-dee
                    wrote on last edited by
                    #9

                    [quote author="Gerolf" date="1304067659"]If you then emit inside your class, it did not work? strange... should do logically the same as QMetaObject::invokeMethod[/quote]

                    That was the first thing i tried, from what i read i thought it should work. But the code never reached the slot function

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                    • G Offline
                      G Offline
                      giesbert
                      wrote on last edited by
                      #10

                      [quote author="bazz-dee" date="1304068700"]
                      [quote author="Gerolf" date="1304067659"]If you then emit inside your class, it did not work? strange... should do logically the same as QMetaObject::invokeMethod[/quote]

                      That was the first thing i tried, from what i read i thought it should work. But the code never reached the slot function[/quote]

                      perhaps, the code was wrong? Did you add the parameter types inmj signals and also the brackets? param,eter trypes in the slot ?

                      @
                      connect(this, SIGNAL(xyz(type1, type2)), this SLOT(xyz()));
                      @

                      Nokia Certified Qt Specialist.
                      Programming Is Like Sex: One mistake and you have to support it for the rest of your life. (Michael Sinz)

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                      • B Offline
                        B Offline
                        bazz-dee
                        wrote on last edited by
                        #11

                        i had the parameters in both

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                        • G Offline
                          G Offline
                          giesbert
                          wrote on last edited by
                          #12

                          only the types, or also the parameter names?

                          Nokia Certified Qt Specialist.
                          Programming Is Like Sex: One mistake and you have to support it for the rest of your life. (Michael Sinz)

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                          0
                          • B Offline
                            B Offline
                            bazz-dee
                            wrote on last edited by
                            #13

                            only the types. i still have it running with signals/slots where the signals are emitted from the GUI thread

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