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Executing QProcess in QThread: memory leak

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  • Christian EhrlicherC Online
    Christian EhrlicherC Online
    Christian Ehrlicher
    Lifetime Qt Champion
    wrote on last edited by
    #30

    QProcess is asynchronous.

    Qt Online Installer direct download: https://download.qt.io/official_releases/online_installers/
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    sitesvS 1 Reply Last reply
    1
    • Christian EhrlicherC Christian Ehrlicher

      QProcess is asynchronous.

      sitesvS Offline
      sitesvS Offline
      sitesv
      wrote on last edited by
      #31

      @Christian-Ehrlicher said in Executing QProcess in QThread: memory leak:

      QProcess is asynchronous.

      "waitForFinished" is not help?

      Christian EhrlicherC 1 Reply Last reply
      0
      • sitesvS sitesv

        @Christian-Ehrlicher said in Executing QProcess in QThread: memory leak:

        QProcess is asynchronous.

        "waitForFinished" is not help?

        Christian EhrlicherC Online
        Christian EhrlicherC Online
        Christian Ehrlicher
        Lifetime Qt Champion
        wrote on last edited by
        #32

        @sitesv said in Executing QProcess in QThread: memory leak:

        "waitForFinished" is not help?

        Why do you want to make a asynchronous object blocking? Please read the QProcess docs and use the proper signals.

        Qt Online Installer direct download: https://download.qt.io/official_releases/online_installers/
        Visit the Qt Academy at https://academy.qt.io/catalog

        1 Reply Last reply
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        • SGaistS Offline
          SGaistS Offline
          SGaist
          Lifetime Qt Champion
          wrote on last edited by
          #33

          The thing is: you just ping in the void, you do not even do anything with that information so why even ping ?

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          Please read the Qt Code of Conduct - https://forum.qt.io/topic/113070/qt-code-of-conduct

          sitesvS 1 Reply Last reply
          1
          • SGaistS SGaist

            The thing is: you just ping in the void, you do not even do anything with that information so why even ping ?

            sitesvS Offline
            sitesvS Offline
            sitesv
            wrote on last edited by
            #34

            @SGaist said in Executing QProcess in QThread: memory leak:

            The thing is: you just ping in the void, you do not even do anything with that information so why even ping ?

            I just skipped this code, it is unimportant... It receives an answer, analyzes it, and emits a signal to the main thread. And this is works.

            JonBJ SGaistS 2 Replies Last reply
            0
            • sitesvS sitesv

              @SGaist said in Executing QProcess in QThread: memory leak:

              The thing is: you just ping in the void, you do not even do anything with that information so why even ping ?

              I just skipped this code, it is unimportant... It receives an answer, analyzes it, and emits a signal to the main thread. And this is works.

              JonBJ Offline
              JonBJ Offline
              JonB
              wrote on last edited by
              #35

              @sitesv
              As @Christian-Ehrlicher has said. You are using this thread to run a QProcess, and you call waitForFinished() on it. You would be better just running QProcess asynchronously from your main thread, and acting on signals. Then perhaps any thread memory issue will go away.

              sitesvS 1 Reply Last reply
              1
              • JonBJ JonB

                @sitesv
                As @Christian-Ehrlicher has said. You are using this thread to run a QProcess, and you call waitForFinished() on it. You would be better just running QProcess asynchronously from your main thread, and acting on signals. Then perhaps any thread memory issue will go away.

                sitesvS Offline
                sitesvS Offline
                sitesv
                wrote on last edited by
                #36

                @JonB
                I will try it.

                1 Reply Last reply
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                • sitesvS sitesv

                  @SGaist said in Executing QProcess in QThread: memory leak:

                  The thing is: you just ping in the void, you do not even do anything with that information so why even ping ?

                  I just skipped this code, it is unimportant... It receives an answer, analyzes it, and emits a signal to the main thread. And this is works.

                  SGaistS Offline
                  SGaistS Offline
                  SGaist
                  Lifetime Qt Champion
                  wrote on last edited by
                  #37

                  @sitesv said in Executing QProcess in QThread: memory leak:

                  @SGaist said in Executing QProcess in QThread: memory leak:

                  The thing is: you just ping in the void, you do not even do anything with that information so why even ping ?

                  I just skipped this code, it is unimportant... It receives an answer, analyzes it, and emits a signal to the main thread. And this is works.

                  Well, do not skip that kind of details when asking questions, it can hide the issue you are asking help for and it does not allow people to understand what is really happening.

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

                  sitesvS 1 Reply Last reply
                  0
                  • SGaistS SGaist

                    @sitesv said in Executing QProcess in QThread: memory leak:

                    @SGaist said in Executing QProcess in QThread: memory leak:

                    The thing is: you just ping in the void, you do not even do anything with that information so why even ping ?

                    I just skipped this code, it is unimportant... It receives an answer, analyzes it, and emits a signal to the main thread. And this is works.

                    Well, do not skip that kind of details when asking questions, it can hide the issue you are asking help for and it does not allow people to understand what is really happening.

                    sitesvS Offline
                    sitesvS Offline
                    sitesv
                    wrote on last edited by
                    #38

                    @SGaist code updated

                    KroMignonK 1 Reply Last reply
                    0
                    • sitesvS sitesv

                      @KroMignon Thank you for your variant.
                      I have some Qs;
                      Why you are using QTimer for this purpose?
                      doPing() is represents my code with using QProcess?
                      This class should create in the main thread?

                      KroMignonK Offline
                      KroMignonK Offline
                      KroMignon
                      wrote on last edited by KroMignon
                      #39

                      @sitesv said in Executing QProcess in QThread: memory leak:

                      Why you are using QTimer for this purpose?

                      I use QTimer here to make a passive wait. When the interval is reached, the QTimer fires the timeout() event. This will not lock the event queue. QThread::msleep() is an active wait ==> CPU usage for nothing and no signals/slots handling possible for the used thread!

                      doPing() is represents my code with using QProcess?

                      Yes, but I would not use a pointer for the QProcess.

                      This class should create in the main thread?

                      As you like. The QTimer instance has this as parent, moving the PingTester instance to another thread, will also move the QTimer instance to the same thread.

                      It is an old maxim of mine that when you have excluded the impossible, whatever remains, however improbable, must be the truth. (Sherlock Holmes)

                      1 Reply Last reply
                      1
                      • sitesvS sitesv

                        @SGaist code updated

                        KroMignonK Offline
                        KroMignonK Offline
                        KroMignon
                        wrote on last edited by
                        #40

                        @sitesv For example a possible implementation which will not lock the event loop could be:

                        void PingTester::doPing()
                        {		
                            QProcess ping;
                            QEventLoop l; // used for passive wait until process finished
                        
                            ping.setProcessChannelMode(QProcess::MergedChannels);
                            connect(&ping, &QProcess::finished, 
                                    [this, &l, &ping]() {
                                        QString output(ping.readAll());
                                        if(output.contains("ttl",Qt::CaseInsensitive))
                                            emit pingSuccess();
                                        else
                                            emit pingFailure();
                                        // exit event loop on process end
                                        l.exit();
                                    });
                            // starting ping request
                            ping.start("/bin/ping", QStringList() << "127.0.0.1" << "-c" << "1");
                        
                            // wait until ping finished
                            l.exec();
                        
                            // start next ping (timer should be configured as single shot)
                            m_timer->start();
                        }
                        

                        It is an old maxim of mine that when you have excluded the impossible, whatever remains, however improbable, must be the truth. (Sherlock Holmes)

                        sitesvS 1 Reply Last reply
                        1
                        • KroMignonK KroMignon

                          @sitesv For example a possible implementation which will not lock the event loop could be:

                          void PingTester::doPing()
                          {		
                              QProcess ping;
                              QEventLoop l; // used for passive wait until process finished
                          
                              ping.setProcessChannelMode(QProcess::MergedChannels);
                              connect(&ping, &QProcess::finished, 
                                      [this, &l, &ping]() {
                                          QString output(ping.readAll());
                                          if(output.contains("ttl",Qt::CaseInsensitive))
                                              emit pingSuccess();
                                          else
                                              emit pingFailure();
                                          // exit event loop on process end
                                          l.exit();
                                      });
                              // starting ping request
                              ping.start("/bin/ping", QStringList() << "127.0.0.1" << "-c" << "1");
                          
                              // wait until ping finished
                              l.exec();
                          
                              // start next ping (timer should be configured as single shot)
                              m_timer->start();
                          }
                          
                          sitesvS Offline
                          sitesvS Offline
                          sitesv
                          wrote on last edited by
                          #41

                          @KroMignon Thank you for the new experience.
                          There is a problem with 'connect'

                          KroMignonK 1 Reply Last reply
                          0
                          • sitesvS sitesv

                            @KroMignon Thank you for the new experience.
                            There is a problem with 'connect'

                            KroMignonK Offline
                            KroMignonK Offline
                            KroMignon
                            wrote on last edited by
                            #42

                            @sitesv said in Executing QProcess in QThread: memory leak:

                            There is a problem with 'connect'

                            Can you detail more the problem?

                            It is an old maxim of mine that when you have excluded the impossible, whatever remains, however improbable, must be the truth. (Sherlock Holmes)

                            sitesvS 1 Reply Last reply
                            0
                            • KroMignonK KroMignon

                              @sitesv said in Executing QProcess in QThread: memory leak:

                              There is a problem with 'connect'

                              Can you detail more the problem?

                              sitesvS Offline
                              sitesvS Offline
                              sitesv
                              wrote on last edited by
                              #43

                              @KroMignon said in Executing QProcess in QThread: memory leak:

                              Can you detail more the problem?

                              pingtester.cpp:9:5: error: no matching member function for call to 'connect'
                              qobject.h:481:41: note: candidate function not viable: no overload of 'finished' matching 'const char *' for 2nd argument
                              qobject.h:274:13: note: candidate template ignored: couldn't infer template argument 'Func1'
                              qobject.h:314:13: note: candidate template ignored: couldn't infer template argument 'Func1'
                              qobject.h:242:43: note: candidate function template not viable: requires at least 4 arguments, but 3 were provided
                              qobject.h:283:13: note: candidate function template not viable: requires at least 4 arguments, but 3 were provided
                              qobject.h:322:13: note: candidate function template not viable: requires at least 4 arguments, but 3 were provided
                              qobject.h:222:36: note: candidate function not viable: requires at least 4 arguments, but 3 were provided
                              qobject.h:225:36: note: candidate function not viable: requires at least 4 arguments, but 3 were provided

                              KroMignonK 1 Reply Last reply
                              0
                              • sitesvS sitesv

                                @KroMignon said in Executing QProcess in QThread: memory leak:

                                Can you detail more the problem?

                                pingtester.cpp:9:5: error: no matching member function for call to 'connect'
                                qobject.h:481:41: note: candidate function not viable: no overload of 'finished' matching 'const char *' for 2nd argument
                                qobject.h:274:13: note: candidate template ignored: couldn't infer template argument 'Func1'
                                qobject.h:314:13: note: candidate template ignored: couldn't infer template argument 'Func1'
                                qobject.h:242:43: note: candidate function template not viable: requires at least 4 arguments, but 3 were provided
                                qobject.h:283:13: note: candidate function template not viable: requires at least 4 arguments, but 3 were provided
                                qobject.h:322:13: note: candidate function template not viable: requires at least 4 arguments, but 3 were provided
                                qobject.h:222:36: note: candidate function not viable: requires at least 4 arguments, but 3 were provided
                                qobject.h:225:36: note: candidate function not viable: requires at least 4 arguments, but 3 were provided

                                KroMignonK Offline
                                KroMignonK Offline
                                KroMignon
                                wrote on last edited by
                                #44

                                @sitesv Oh, my bad, QProcess::finished() has an overload (https://doc.qt.io/qt-5/qprocess.html#finished)

                                Should be changed to:

                                connect(&ping, QOverload<int, QProcess::ExitStatus>::of(&QProcess::finished), 
                                            [this, &l, &ping]() {
                                                QString output(ping.readAll());
                                                if(output.contains("ttl",Qt::CaseInsensitive))
                                                    emit pingSuccess();
                                                else
                                                    emit pingFailure();
                                                // exit event loop on process end
                                                l.exit();
                                            }); 
                                

                                It is an old maxim of mine that when you have excluded the impossible, whatever remains, however improbable, must be the truth. (Sherlock Holmes)

                                1 Reply Last reply
                                1
                                • sitesvS Offline
                                  sitesvS Offline
                                  sitesv
                                  wrote on last edited by
                                  #45

                                  @KroMignon
                                  Very interesting realization. I will study it.
                                  Thank you again!

                                  1 Reply Last reply
                                  0
                                  • sitesvS Offline
                                    sitesvS Offline
                                    sitesv
                                    wrote on last edited by sitesv
                                    #46

                                    @KroMignon
                                    Hi!
                                    Is it possible to make a checking ping of a list of addresses for each timer interval? I haven't used a lambda yet in my practice ((.

                                    KroMignonK 1 Reply Last reply
                                    0
                                    • sitesvS sitesv

                                      @KroMignon
                                      Hi!
                                      Is it possible to make a checking ping of a list of addresses for each timer interval? I haven't used a lambda yet in my practice ((.

                                      KroMignonK Offline
                                      KroMignonK Offline
                                      KroMignon
                                      wrote on last edited by KroMignon
                                      #47

                                      @sitesv said in Executing QProcess in QThread: memory leak:

                                      Is it possible to make a checking ping of a list of addresses for each timer interval? I haven't used a lambda yet in my practice ((.

                                      Yes, it is possible.
                                      I have give you a basic implementation example.
                                      You just have to complete it.

                                      If you want to learn lambda, search on internet, there are many explanations. It is not so hard to understand.
                                      My favorite is https://blog.feabhas.com/2014/03/demystifying-c-lambdas/

                                      It is an old maxim of mine that when you have excluded the impossible, whatever remains, however improbable, must be the truth. (Sherlock Holmes)

                                      sitesvS 1 Reply Last reply
                                      3
                                      • KroMignonK KroMignon

                                        @sitesv said in Executing QProcess in QThread: memory leak:

                                        Is it possible to make a checking ping of a list of addresses for each timer interval? I haven't used a lambda yet in my practice ((.

                                        Yes, it is possible.
                                        I have give you a basic implementation example.
                                        You just have to complete it.

                                        If you want to learn lambda, search on internet, there are many explanations. It is not so hard to understand.
                                        My favorite is https://blog.feabhas.com/2014/03/demystifying-c-lambdas/

                                        sitesvS Offline
                                        sitesvS Offline
                                        sitesv
                                        wrote on last edited by
                                        #48

                                        @KroMignon said in Executing QProcess in QThread: memory leak:

                                        Yes, it is possible.

                                        I have tried to do something like this. But is execute too slow.

                                        QStringList ip_list = {"192.168.0.1", "192.168.0.2"};
                                            int success_count = 0;
                                            foreach(auto ip, ip_list)
                                            {
                                                QProcess ping;
                                                QEventLoop l;
                                                ping.setProcessChannelMode(QProcess::MergedChannels);
                                                connect(&ping,
                                                        QOverload<int, QProcess::ExitStatus>::of(&QProcess::finished),
                                                        [&l, &ping, &success_count]() {
                                                            QString output(ping.readAll());
                                                            if(output.contains("ttl",Qt::CaseInsensitive)) success_count++;
                                                            l.exit();
                                                        });
                                                ping.start("/bin/ping", QStringList() << ip << "-c" << "1");
                                                l.exec();
                                            }
                                            if(success_count == ip_list.count())
                                               emit setStatus(true);
                                            else
                                               emit setStatus(false);
                                            m_timer->start();
                                        
                                        jsulmJ 1 Reply Last reply
                                        0
                                        • sitesvS sitesv

                                          @KroMignon said in Executing QProcess in QThread: memory leak:

                                          Yes, it is possible.

                                          I have tried to do something like this. But is execute too slow.

                                          QStringList ip_list = {"192.168.0.1", "192.168.0.2"};
                                              int success_count = 0;
                                              foreach(auto ip, ip_list)
                                              {
                                                  QProcess ping;
                                                  QEventLoop l;
                                                  ping.setProcessChannelMode(QProcess::MergedChannels);
                                                  connect(&ping,
                                                          QOverload<int, QProcess::ExitStatus>::of(&QProcess::finished),
                                                          [&l, &ping, &success_count]() {
                                                              QString output(ping.readAll());
                                                              if(output.contains("ttl",Qt::CaseInsensitive)) success_count++;
                                                              l.exit();
                                                          });
                                                  ping.start("/bin/ping", QStringList() << ip << "-c" << "1");
                                                  l.exec();
                                              }
                                              if(success_count == ip_list.count())
                                                 emit setStatus(true);
                                              else
                                                 emit setStatus(false);
                                              m_timer->start();
                                          
                                          jsulmJ Offline
                                          jsulmJ Offline
                                          jsulm
                                          Lifetime Qt Champion
                                          wrote on last edited by
                                          #49
                                          This post is deleted!
                                          1 Reply Last reply
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