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main and background thread example

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  • SGaistS SGaist

    Did you check the memory used by you application ?

    U Offline
    U Offline
    user4592357
    wrote on last edited by user4592357
    #10

    @SGaist

    what do you mean by check? and no, how should i?

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    • SGaistS Offline
      SGaistS Offline
      SGaist
      Lifetime Qt Champion
      wrote on last edited by
      #11

      Using the top command for example. Valgrind etc.

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

      U 1 Reply Last reply
      1
      • SGaistS SGaist

        Using the top command for example. Valgrind etc.

        U Offline
        U Offline
        user4592357
        wrote on last edited by
        #12

        @SGaist

        okay, thanks.
        one last question, as you can see, on timer's timeout i execute a function. is it possible stop the timer (so the function won't be executed), and then restart it again?

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        • SGaistS Offline
          SGaistS Offline
          SGaist
          Lifetime Qt Champion
          wrote on last edited by
          #13

          Yes:
          QTimer::stop
          QTimer::start

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

          U 1 Reply Last reply
          3
          • SGaistS SGaist

            Yes:
            QTimer::stop
            QTimer::start

            U Offline
            U Offline
            user4592357
            wrote on last edited by
            #14

            @SGaist

            hi again,
            i ran valgrind and it says there's a memory leak on exec() which is in run() overridden method. so what's wrong?

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            • U user4592357

              i wanna write a basic thread example. here's the idea:
              i have the main event loop. before calling app.exec(), i create an object which itself creates an object and puts it in a separate thread for running. i need some way to tell the background thread that main thread has finished (to join()), so i have a bool to indicate that.

              however, when the application exits, something goes wrong. i'm running it using visual studio and the debugging session won't stop. i don't understand what's wrong. here's the code:

              #include <QApplication>
              #include <QObject>
              #include <QThread>
              #include <iostream>
              #include <thread>
              #include <QtWidgets/QLabel>
              #include <atomic>
              
              std::atomic<bool> bMainThreadRunning { true };
              
              class ThreadObj {
              public:
              	void work() {
              		while(bMainThreadRunning) {
              			++counter;
              			std::this_thread::sleep_for(std::chrono::seconds(5));
              		}
              	}
              private:
              	int counter { 0 };
              };
              
              class Obj {
              public:
              	void start() {
              		ThreadObj obj;
              		m_thread = std::thread(&ThreadObj::work, &obj);
              	}
              	void onMainThreadFinished() {
              		bMainThreadRunning = true;
              		m_thread.join();
              	}
              private:
              	std::thread m_thread;
              };
              
              int main(int argc, char *argv[])
              {
              	QApplication a(argc, argv);
              	Obj o;
              	o.start();
              
              	QWidget w;
              	w.show();
              
              	auto ret = a.exec();
              	o.onMainThreadFinished();
              
              	return 0;
              }
              
              VRoninV Offline
              VRoninV Offline
              VRonin
              wrote on last edited by
              #15

              @user4592357 said in main and background thread example:

              ThreadObj obj;
              m_thread = std::thread(&ThreadObj::work, &obj);

              obj is allocated on the stack, it will go out of scope and delete itself

              "La mort n'est rien, mais vivre vaincu et sans gloire, c'est mourir tous les jours"
              ~Napoleon Bonaparte

              On a crusade to banish setIndexWidget() from the holy land of Qt

              U 1 Reply Last reply
              3
              • VRoninV VRonin

                @user4592357 said in main and background thread example:

                ThreadObj obj;
                m_thread = std::thread(&ThreadObj::work, &obj);

                obj is allocated on the stack, it will go out of scope and delete itself

                U Offline
                U Offline
                user4592357
                wrote on last edited by
                #16

                @VRonin

                hi, thanks for the reply.
                the code has been modified since the first post (see my last code-post), so it's not the problem

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                • VRoninV Offline
                  VRoninV Offline
                  VRonin
                  wrote on last edited by
                  #17

                  https://mayaposch.wordpress.com/2011/11/01/how-to-really-truly-use-qthreads-the-full-explanation/

                  "La mort n'est rien, mais vivre vaincu et sans gloire, c'est mourir tous les jours"
                  ~Napoleon Bonaparte

                  On a crusade to banish setIndexWidget() from the holy land of Qt

                  U 1 Reply Last reply
                  0
                  • VRoninV VRonin

                    https://mayaposch.wordpress.com/2011/11/01/how-to-really-truly-use-qthreads-the-full-explanation/

                    U Offline
                    U Offline
                    user4592357
                    wrote on last edited by
                    #18

                    @VRonin

                    i've read similar articles, saying "you shouldn't subclass QThread". in my case i need to do that.

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                    0
                    • SGaistS Offline
                      SGaistS Offline
                      SGaist
                      Lifetime Qt Champion
                      wrote on last edited by SGaist
                      #19

                      Out of curiosity, what are you doing that requires to subclass QThread ?

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

                      U 1 Reply Last reply
                      0
                      • SGaistS SGaist

                        Out of curiosity, what are you doing that requires to subclass QThread ?

                        U Offline
                        U Offline
                        user4592357
                        wrote on last edited by
                        #20

                        @SGaist

                        nothing requires it. it's just that the whole implementation is done and i don't wanna change everything

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