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threads and created objects

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  • SGaistS SGaist

    Object belonging and thread affinity are different things.

    The message you had was because the destruction happened in the main thread.

    mzimmersM Offline
    mzimmersM Offline
    mzimmers
    wrote on last edited by
    #14

    @SGaist said in threads and created objects:

    Object belonging and thread affinity are different things.

    I need to pursue this a bit further. So, if I have an object (my worker object) that I move to another thread, is it true that anything created within that object prior to the move "belongs" to the original thread?

    Specifically, my worker object has a member object m_serial. Presumably this object belongs to the original thread. After worker is moved, when this object creates something (like a QSerialPort), this "belongs" to the worker thread. When the worker thread does a write on it, I get the timer error. Is this because m_serial belongs to the original thread, but its QSerialPort belongs to the worker thread?

    And if I have this right, is the solution that the worker thread would create its objects in start(), instead of having member objects?

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    • SGaistS Offline
      SGaistS Offline
      SGaist
      Lifetime Qt Champion
      wrote on last edited by SGaist
      #15

      @mzimmers said in threads and created objects:

      I need to pursue this a bit further. So, if I have an object (my worker object) that I move to another thread, is it true that anything created within that object prior to the move "belongs" to the original thread?

      If it's a QObject that is properly parented, it will move with it. Note that classes like QTcpSocket must be created in the new thread. You can however pass the descriptor like shown in the threaded QTcpSocket/Server example.

      Interested in AI ? www.idiap.ch
      Please read the Qt Code of Conduct - https://forum.qt.io/topic/113070/qt-code-of-conduct

      kshegunovK mzimmersM 2 Replies Last reply
      1
      • SGaistS SGaist

        @mzimmers said in threads and created objects:

        I need to pursue this a bit further. So, if I have an object (my worker object) that I move to another thread, is it true that anything created within that object prior to the move "belongs" to the original thread?

        If it's a QObject that is properly parented, it will move with it. Note that classes like QTcpSocket must be created in the new thread. You can however pass the descriptor like shown in the threaded QTcpSocket/Server example.

        kshegunovK Offline
        kshegunovK Offline
        kshegunov
        Moderators
        wrote on last edited by
        #16

        @SGaist said in threads and created objects:

        If it's a QObject that is properly patented, it will move with it. Note that classes like QTcoSocket must be created in the new thread. You can however pass the descriptor like shown in the threaded QTcpSocket/Server example.

        Actually a comment on that. Sockets that haven't been opened/bound can still be moved normally, however I agree it's a bad practice to depend on the actual implementation.

        Read and abide by the Qt Code of Conduct

        1 Reply Last reply
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        • SGaistS SGaist

          @mzimmers said in threads and created objects:

          I need to pursue this a bit further. So, if I have an object (my worker object) that I move to another thread, is it true that anything created within that object prior to the move "belongs" to the original thread?

          If it's a QObject that is properly parented, it will move with it. Note that classes like QTcpSocket must be created in the new thread. You can however pass the descriptor like shown in the threaded QTcpSocket/Server example.

          mzimmersM Offline
          mzimmersM Offline
          mzimmers
          wrote on last edited by
          #17

          @SGaist said in threads and created objects:

          If it's a QObject that is properly patented, it will move with it.

          This is my current creation:

          class Worker : public QObject
          {
              Q_OBJECT
          private:
              SerialPort m_serial;
          ...
          SerialPort::SerialPort(QObject *parent) : QObject (parent)
          {
          ...
          

          Note that classes like QTcoSocket must be created in the new thread.

          But not in the c'tor, correct? Because that is called prior to the thread move, so it would pertain to the original thread?

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          • SGaistS Offline
            SGaistS Offline
            SGaist
            Lifetime Qt Champion
            wrote on last edited by
            #18

            I fixed the typo of parented (damn autocorrect...)

            Yes, m_serial will not be moved.

            Interested in AI ? www.idiap.ch
            Please read the Qt Code of Conduct - https://forum.qt.io/topic/113070/qt-code-of-conduct

            mzimmersM 1 Reply Last reply
            2
            • SGaistS SGaist

              I fixed the typo of parented (damn autocorrect...)

              Yes, m_serial will not be moved.

              mzimmersM Offline
              mzimmersM Offline
              mzimmers
              wrote on last edited by mzimmers
              #19

              @SGaist said in threads and created objects:

              I fixed the typo of parented (damn autocorrect...

              Well, while you're at it..."QTcoSocket?"

              kshegunovK SGaistS 2 Replies Last reply
              0
              • mzimmersM mzimmers

                @SGaist said in threads and created objects:

                I fixed the typo of parented (damn autocorrect...

                Well, while you're at it..."QTcoSocket?"

                kshegunovK Offline
                kshegunovK Offline
                kshegunov
                Moderators
                wrote on last edited by kshegunov
                #20

                If you want the QObjects to to be moved alongside with their parent to another thread, then you must pass them the parent. No parent, no way Qt to know whether the object's supposed to be moved.

                Read and abide by the Qt Code of Conduct

                mzimmersM 1 Reply Last reply
                0
                • mzimmersM mzimmers

                  @SGaist said in threads and created objects:

                  I fixed the typo of parented (damn autocorrect...

                  Well, while you're at it..."QTcoSocket?"

                  SGaistS Offline
                  SGaistS Offline
                  SGaist
                  Lifetime Qt Champion
                  wrote on last edited by
                  #21

                  @mzimmers said in threads and created objects:

                  @SGaist said in threads and created objects:

                  I fixed the typo of parented (damn autocorrect...

                  Well, while you're at it..."QTcoSocket?"

                  Argle........ Done

                  Interested in AI ? www.idiap.ch
                  Please read the Qt Code of Conduct - https://forum.qt.io/topic/113070/qt-code-of-conduct

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                  0
                  • kshegunovK kshegunov

                    If you want the QObjects to to be moved alongside with their parent to another thread, then you must pass them the parent. No parent, no way Qt to know whether the object's supposed to be moved.

                    mzimmersM Offline
                    mzimmersM Offline
                    mzimmers
                    wrote on last edited by mzimmers
                    #22

                    @kshegunov I don't know how to do that in this case. If my SerialPort object is defined:

                    class SerialPort : public QObject
                    {
                        Q_OBJECT
                    public:
                        explicit SerialPort(Worker *parent = nullptr);
                    ...
                    SerialPort::SerialPort(Worker *parent) : QObject(parent)
                    

                    Then how do I declare an instance of SerialPort in my worker object? If I do it like this:

                        SerialPort m_serial;
                    

                    Then it doesn't seem to get moved.

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                    • SGaistS Offline
                      SGaistS Offline
                      SGaist
                      Lifetime Qt Champion
                      wrote on last edited by
                      #23

                      The usual: pointer and allocate it in the constructor with a parent.

                      Interested in AI ? www.idiap.ch
                      Please read the Qt Code of Conduct - https://forum.qt.io/topic/113070/qt-code-of-conduct

                      mzimmersM 1 Reply Last reply
                      0
                      • SGaistS SGaist

                        The usual: pointer and allocate it in the constructor with a parent.

                        mzimmersM Offline
                        mzimmersM Offline
                        mzimmers
                        wrote on last edited by
                        #24

                        @SGaist OK, thanks. I had (incorrectly) inferred from kshegunov's post that it somehow could be done as an ordinary member variable.

                        kshegunovK 1 Reply Last reply
                        0
                        • mzimmersM mzimmers

                          @SGaist OK, thanks. I had (incorrectly) inferred from kshegunov's post that it somehow could be done as an ordinary member variable.

                          kshegunovK Offline
                          kshegunovK Offline
                          kshegunov
                          Moderators
                          wrote on last edited by
                          #25

                          @mzimmers No the inference is correct. This shall work, shan't it?

                          class Worker : public QObject
                          {
                              Q_OBJECT
                          public:
                              Worker();
                          private:
                              SerialPort m_serial;
                          };
                          
                          Worker::Worker()
                              : m_serial(this)
                          {
                          }
                          

                          Read and abide by the Qt Code of Conduct

                          mzimmersM 1 Reply Last reply
                          2
                          • kshegunovK kshegunov

                            @mzimmers No the inference is correct. This shall work, shan't it?

                            class Worker : public QObject
                            {
                                Q_OBJECT
                            public:
                                Worker();
                            private:
                                SerialPort m_serial;
                            };
                            
                            Worker::Worker()
                                : m_serial(this)
                            {
                            }
                            
                            mzimmersM Offline
                            mzimmersM Offline
                            mzimmers
                            wrote on last edited by
                            #26

                            @kshegunov well...yes it does. I was missing the " : m_serial(this)" clause. Thanks!

                            1 Reply Last reply
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