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Executing QProcess in QThread: memory leak

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  • 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
                      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?

                        KroMignonK Offline
                        KroMignonK Offline
                        KroMignon
                        wrote on last edited by
                        #54

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

                        How to set a timeout for the process execution in this case?

                        Have you tried to look at ping parameters (ping --help)

                        And I would only wait once, for all pings to be done:

                        QStringList ip_list = {"192.168.0.1", "192.168.0.2"};
                        int success_count = 0;
                        int pingsToDo = ip_list.count();
                        QEventLoop l;
                        foreach(auto ip, ip_list)
                        {
                            QProcess ping;
                            ping.setProcessChannelMode(QProcess::MergedChannels);
                            connect(&ping,
                                    QOverload<int, QProcess::ExitStatus>::of(&QProcess::finished),
                                    [&l, &ping, &success_count, &pingsToDo]() {
                                        --pingsToDo;
                                        QString output(ping.readAll());
                                        if(output.contains("ttl",Qt::CaseInsensitive)) success_count++;
                                        if(!pingsToDo)
                                            l.exit();
                                    });
                            ping.start("/bin/ping", QStringList() << ip << "-c" << "1");
                        }
                        
                        // wait all pings done
                        l.exec();
                        if(success_count == ip_list.count())
                           emit setStatus(true);
                        else
                           emit setStatus(false);
                        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 said in Executing QProcess in QThread: memory leak:

                          How to set a timeout for the process execution in this case?

                          Have you tried to look at ping parameters (ping --help)

                          And I would only wait once, for all pings to be done:

                          QStringList ip_list = {"192.168.0.1", "192.168.0.2"};
                          int success_count = 0;
                          int pingsToDo = ip_list.count();
                          QEventLoop l;
                          foreach(auto ip, ip_list)
                          {
                              QProcess ping;
                              ping.setProcessChannelMode(QProcess::MergedChannels);
                              connect(&ping,
                                      QOverload<int, QProcess::ExitStatus>::of(&QProcess::finished),
                                      [&l, &ping, &success_count, &pingsToDo]() {
                                          --pingsToDo;
                                          QString output(ping.readAll());
                                          if(output.contains("ttl",Qt::CaseInsensitive)) success_count++;
                                          if(!pingsToDo)
                                              l.exit();
                                      });
                              ping.start("/bin/ping", QStringList() << ip << "-c" << "1");
                          }
                          
                          // wait all pings done
                          l.exec();
                          if(success_count == ip_list.count())
                             emit setStatus(true);
                          else
                             emit setStatus(false);
                          m_timer->start();
                          
                          sitesvS Offline
                          sitesvS Offline
                          sitesv
                          wrote on last edited by sitesv
                          #55

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

                          And I would only wait once, for all pings to be done:

                          Wow! Very nice!! Thank you!

                          @KroMignon
                          UPD: app is freezing on line l.exec() althought l.exit() is done....

                          1 Reply Last reply
                          0
                          • sitesvS Offline
                            sitesvS Offline
                            sitesv
                            wrote on last edited by
                            #56

                            Guys, how to resolve this?

                            KroMignonK 1 Reply Last reply
                            0
                            • sitesvS sitesv

                              Guys, how to resolve this?

                              KroMignonK Offline
                              KroMignonK Offline
                              KroMignon
                              wrote on last edited by
                              #57

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

                              Guys, how to resolve this?

                              Hmm, I think it is a tricky issue. I would start with forcing QueuedConnection, to avoid threading issues:

                              connect(&ping,
                                          QOverload<int, QProcess::ExitStatus>::of(&QProcess::finished),
                                          [&l, &ping, &success_count, &pingsToDo]() {
                                              ...
                                          }, Qt::QueuedConnection);
                              

                              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:

                                Guys, how to resolve this?

                                Hmm, I think it is a tricky issue. I would start with forcing QueuedConnection, to avoid threading issues:

                                connect(&ping,
                                            QOverload<int, QProcess::ExitStatus>::of(&QProcess::finished),
                                            [&l, &ping, &success_count, &pingsToDo]() {
                                                ...
                                            }, Qt::QueuedConnection);
                                
                                sitesvS Offline
                                sitesvS Offline
                                sitesv
                                wrote on last edited by
                                #58

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

                                connect(&ping,
                                QOverload<int, QProcess::ExitStatus>::of(&QProcess::finished),
                                &l, &ping, &success_count, &pingsToDo {
                                ...
                                }, Qt::QueuedConnection);

                                'connect' failed again
                                img1.png

                                KroMignonK 2 Replies Last reply
                                0
                                • sitesvS sitesv

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

                                  connect(&ping,
                                  QOverload<int, QProcess::ExitStatus>::of(&QProcess::finished),
                                  &l, &ping, &success_count, &pingsToDo {
                                  ...
                                  }, Qt::QueuedConnection);

                                  'connect' failed again
                                  img1.png

                                  KroMignonK Offline
                                  KroMignonK Offline
                                  KroMignon
                                  wrote on last edited by KroMignon
                                  #59

                                  @sitesv Can you show the code you have written

                                  Sorry my fault, should be:

                                  connect(&ping,
                                          QOverload<int, QProcess::ExitStatus>::of(&QProcess::finished),
                                          &l, // receiver!
                                          [&l, &ping, &success_count, &pingsToDo]() {
                                              ...
                                          }, Qt::QueuedConnection);
                                  

                                  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 Can you show the code you have written

                                    Sorry my fault, should be:

                                    connect(&ping,
                                            QOverload<int, QProcess::ExitStatus>::of(&QProcess::finished),
                                            &l, // receiver!
                                            [&l, &ping, &success_count, &pingsToDo]() {
                                                ...
                                            }, Qt::QueuedConnection);
                                    
                                    sitesvS Offline
                                    sitesvS Offline
                                    sitesv
                                    wrote on last edited by
                                    #60

                                    @KroMignon

                                    QStringList ip_list = {"192.168.0.1", "192.168.0.2"};
                                        int success_count = 0;
                                        int pingsToDo = ip_list.count();
                                        QEventLoop l; // used for passive wait until process finished
                                        foreach(auto ip, ip_list)
                                        {
                                            QProcess ping;
                                            ping.setProcessChannelMode(QProcess::MergedChannels);
                                            connect(&ping,
                                                    QOverload<int, QProcess::ExitStatus>::of(&QProcess::finished), &l,
                                                    [&l, &ping, &success_count, &pingsToDo]() {
                                                        --pingsToDo;
                                                        QString output(ping.readAll()); // <<<<<<<<<<<<<<<< SIGSEGV Segmentation fault
                                                        if(output.contains("ttl",Qt::CaseInsensitive)){
                                                            success_count++;
                                                        }
                                                        if(!pingsToDo){
                                                            l.exit();
                                                        }
                                                    }, Qt::QueuedConnection);
                                            ping.start("/bin/ping", QStringList() << ip << "-c" << "1");
                                        }
                                        l.exec();
                                        if(success_count == ip_list.count()) emit setLedStatus(0, 0, true);
                                        else                                 emit setLedStatus(0, 0, false);
                                    
                                        m_timer->start();
                                    
                                    

                                    There is SIGSEGV Segmentation fault on ping.readAll string. :((

                                    1 Reply Last reply
                                    0
                                    • sitesvS sitesv

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

                                      connect(&ping,
                                      QOverload<int, QProcess::ExitStatus>::of(&QProcess::finished),
                                      &l, &ping, &success_count, &pingsToDo {
                                      ...
                                      }, Qt::QueuedConnection);

                                      'connect' failed again
                                      img1.png

                                      KroMignonK Offline
                                      KroMignonK Offline
                                      KroMignon
                                      wrote on last edited by KroMignon
                                      #61

                                      @sitesv Sorry but I was a little bit confused when I suggest you this code.
                                      This cannot work, because QProcess is killed/destroyed at end of the for loop!
                                      Should be:

                                      QStringList ip_list = {"192.168.0.1", "192.168.0.2"};
                                      int success_count = 0;
                                      int pingsToDo = ip_list.count();
                                      QEventLoop l;
                                      foreach(auto ip, ip_list)
                                      {
                                          auto ping = new QProcess();
                                          ping->setProcessChannelMode(QProcess::MergedChannels);
                                          connect(ping,
                                                  QOverload<int, QProcess::ExitStatus>::of(&QProcess::finished),
                                                  [&l, ping, &success_count, &pingsToDo]() {
                                                      --pingsToDo;
                                                      QString output(ping->readAll());
                                                      if(output.contains("ttl",Qt::CaseInsensitive))
                                                          success_count++;
                                                      // free memory
                                                      ping->deleteLater();
                                                      //  exit event loop after all pings done
                                                      if(!pingsToDo)
                                                          l.exit();
                                                  });
                                          ping->start("/bin/ping", QStringList() << ip << "-c" << "1");
                                      }
                                      
                                      // wait all pings done
                                      l.exec();
                                      

                                      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
                                      0
                                      • JonBJ Offline
                                        JonBJ Offline
                                        JonB
                                        wrote on last edited by
                                        #62

                                        @sitesv , @KroMignon
                                        I will say one thing.

                                        You are writing code which will call QEventLoop::exec(), blocking whatever calls it. It relies on hitting the QEventLoop::exit() statement, which you only have in response to the QProcess::finished signal. If for whatever reason that does not get hit, your event loop will never be exited.

                                        I would not write production (or even development) code like this, and certainly not for distribution. It is asking for an "unseen hang" to occur, one day. I would at minimum hook onto QProcess::errorOccurred, maybe stateChanged() too. And I would put in some sort of timer/timeout, so that if something goes badly wrong you get out of the blocking loop (with perhaps an error flag) instead of waiting for Hell to freeze over....

                                        KroMignonK 1 Reply Last reply
                                        3
                                        • JonBJ JonB

                                          @sitesv , @KroMignon
                                          I will say one thing.

                                          You are writing code which will call QEventLoop::exec(), blocking whatever calls it. It relies on hitting the QEventLoop::exit() statement, which you only have in response to the QProcess::finished signal. If for whatever reason that does not get hit, your event loop will never be exited.

                                          I would not write production (or even development) code like this, and certainly not for distribution. It is asking for an "unseen hang" to occur, one day. I would at minimum hook onto QProcess::errorOccurred, maybe stateChanged() too. And I would put in some sort of timer/timeout, so that if something goes badly wrong you get out of the blocking loop (with perhaps an error flag) instead of waiting for Hell to freeze over....

                                          KroMignonK Offline
                                          KroMignonK Offline
                                          KroMignon
                                          wrote on last edited by
                                          #63

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

                                          I would not write production (or even development) code like this, and certainly not for distribution. It is asking for an "unseen hang" to occur, one day. I would at minimum hook onto QProcess::errorOccurred, maybe stateChanged() too. And I would put in some sort of timer/timeout, so that if something goes badly wrong you get out of the blocking loop (with perhaps an error flag) instead of waiting for Hell to freeze over....

                                          Yes, this is a good advice.

                                          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
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