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Executing QProcess in QThread: memory leak

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  • 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
        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.

          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
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              • 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
                                  0
                                  • sitesvS Offline
                                    sitesvS Offline
                                    sitesv
                                    wrote on last edited by sitesv
                                    #50

                                    UPD:
                                    I found the cause of this situation. Ip's are not available. How to set a timeout for the process execution in this case?

                                    jsulmJ KroMignonK 2 Replies Last reply
                                    0
                                    • sitesvS sitesv

                                      UPD:
                                      I found the cause of this situation. Ip's are not available. How to set a timeout for the process execution in this case?

                                      jsulmJ Offline
                                      jsulmJ Offline
                                      jsulm
                                      Lifetime Qt Champion
                                      wrote on last edited by jsulm
                                      #51

                                      @sitesv Why do you actually use a local event loop? You can implement this functionality without blocking your app with a local event loop.
                                      Also, you terminate that event loop already in the first lambda call (when the first process finishes)...

                                      sitesvS 1 Reply Last reply
                                      0
                                      • jsulmJ jsulm

                                        @sitesv Why do you actually use a local event loop? You can implement this functionality without blocking your app with a local event loop.
                                        Also, you terminate that event loop already in the first lambda call (when the first process finishes)...

                                        sitesvS Offline
                                        sitesvS Offline
                                        sitesv
                                        wrote on last edited by
                                        #52

                                        @jsulm Local EventLoop was recommended before. Could you please advise something?

                                        jsulmJ 1 Reply Last reply
                                        0
                                        • sitesvS sitesv

                                          @jsulm Local EventLoop was recommended before. Could you please advise something?

                                          jsulmJ Offline
                                          jsulmJ Offline
                                          jsulm
                                          Lifetime Qt Champion
                                          wrote on last edited by
                                          #53

                                          @sitesv You know how many processes you started. So, count how many processes already finished (inside the lambda). And as soon as all processes finished you can check success_count and emit the signal. All this can be done inside lambda.

                                          1 Reply Last reply
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