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Executing QProcess in QThread: memory leak

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  • jsulmJ jsulm

    @sitesv I'm still wondering why you think you need a local event loop...

    sitesvS Offline
    sitesvS Offline
    sitesv
    wrote on last edited by
    #67

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

    @sitesv I'm still wondering why you think you need a local event loop...

    Hi! I have done variant as you recommend. It's working!

    void PingTester::doPing(){
        QStringList ip_list = {"192.168.0.1", "192.168.0.2"};
        int success_count = 0;
        int pingsToDo = ip_list.count();
        int ipCnt = pingsToDo;
        foreach(auto ip, ip_list)
        {
            QProcess ping;
            ping.setProcessChannelMode(QProcess::MergedChannels);
            connect(&ping,
                    QOverload<int, QProcess::ExitStatus>::of(&QProcess::finished),
                    [this, &ping, &success_count, &pingsToDo, ipCnt]() {
                        --pingsToDo;
                        QString output(ping.readAll());
                        if(output.contains("ttl",Qt::CaseInsensitive)){
                            success_count++;
                        }
                        if(!pingsToDo){
                            if(success_count == ipCnt) emit setStatus(true);
                            else                       emit setStatus(false);
                            m_timer->start();
                        }
                    });
            ping.start("/bin/ping", QStringList() << ip << "-c" << "1" << "-w" << "1");
        }
    }
    

    I made another experiment:

    1. Created a QThread
    2. In QThread::run() method::
    • made a QTimer* object,
    • set him as "one shot kind",
    • ran QTimer, and in final
      * ran QThread::exec() (for run local EventLoop)...
    1. There is timer->start() in timeout slot, It executed, but QTimer doesn't start again.

    Any ideas?

    JonBJ KroMignonK 2 Replies Last reply
    0
    • sitesvS sitesv

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

      @sitesv I'm still wondering why you think you need a local event loop...

      Hi! I have done variant as you recommend. It's working!

      void PingTester::doPing(){
          QStringList ip_list = {"192.168.0.1", "192.168.0.2"};
          int success_count = 0;
          int pingsToDo = ip_list.count();
          int ipCnt = pingsToDo;
          foreach(auto ip, ip_list)
          {
              QProcess ping;
              ping.setProcessChannelMode(QProcess::MergedChannels);
              connect(&ping,
                      QOverload<int, QProcess::ExitStatus>::of(&QProcess::finished),
                      [this, &ping, &success_count, &pingsToDo, ipCnt]() {
                          --pingsToDo;
                          QString output(ping.readAll());
                          if(output.contains("ttl",Qt::CaseInsensitive)){
                              success_count++;
                          }
                          if(!pingsToDo){
                              if(success_count == ipCnt) emit setStatus(true);
                              else                       emit setStatus(false);
                              m_timer->start();
                          }
                      });
              ping.start("/bin/ping", QStringList() << ip << "-c" << "1" << "-w" << "1");
          }
      }
      

      I made another experiment:

      1. Created a QThread
      2. In QThread::run() method::
      • made a QTimer* object,
      • set him as "one shot kind",
      • ran QTimer, and in final
        * ran QThread::exec() (for run local EventLoop)...
      1. There is timer->start() in timeout slot, It executed, but QTimer doesn't start again.

      Any ideas?

      JonBJ Offline
      JonBJ Offline
      JonB
      wrote on last edited by JonB
      #68

      @sitesv
      I don't know how/whether your issue relates this, but in your code: you set off ping.start(), but QProcess ping; is a local variable in your foreach loop and so immediately goes out of scope (not to mention, you also re-use the same local variable for each time round the loop, overwriting/destroying the previous one). Nothing should work (it might actually "crash"), I don't understand how you say it does.

      On top of all of this: I think we've said it already here above, but goodness only knows why you are using a thread, with all the complications that involves? If you want to run a QProcess and the main thread to know when it's finished, it's asynchronous anyway, it would be a whole lot simpler not to have any thread. I think I said this earlier, but up to you.

      And finally, while I'm on a roll: I think you are just using a /bin/ping in order to read the textual output, parse it, and see whether something is there/alive. In which case I'd be tempted to just write it myself in Qt instead of running some external command, I would have thought it's only a few lines of code. Your "parsing" of the output is beyond hokey, not even sure what you think it tells you....

      1 Reply Last reply
      0
      • sitesvS sitesv

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

        @sitesv I'm still wondering why you think you need a local event loop...

        Hi! I have done variant as you recommend. It's working!

        void PingTester::doPing(){
            QStringList ip_list = {"192.168.0.1", "192.168.0.2"};
            int success_count = 0;
            int pingsToDo = ip_list.count();
            int ipCnt = pingsToDo;
            foreach(auto ip, ip_list)
            {
                QProcess ping;
                ping.setProcessChannelMode(QProcess::MergedChannels);
                connect(&ping,
                        QOverload<int, QProcess::ExitStatus>::of(&QProcess::finished),
                        [this, &ping, &success_count, &pingsToDo, ipCnt]() {
                            --pingsToDo;
                            QString output(ping.readAll());
                            if(output.contains("ttl",Qt::CaseInsensitive)){
                                success_count++;
                            }
                            if(!pingsToDo){
                                if(success_count == ipCnt) emit setStatus(true);
                                else                       emit setStatus(false);
                                m_timer->start();
                            }
                        });
                ping.start("/bin/ping", QStringList() << ip << "-c" << "1" << "-w" << "1");
            }
        }
        

        I made another experiment:

        1. Created a QThread
        2. In QThread::run() method::
        • made a QTimer* object,
        • set him as "one shot kind",
        • ran QTimer, and in final
          * ran QThread::exec() (for run local EventLoop)...
        1. There is timer->start() in timeout slot, It executed, but QTimer doesn't start again.

        Any ideas?

        KroMignonK Offline
        KroMignonK Offline
        KroMignon
        wrote on last edited by
        #69

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

        Hi! I have done variant as you recommend. It's working!

        I am not sure this is really working!
        I think you have to (re)learn C++ object life cycle.
        You create a QProcess local instance in the for loop, this object will be destroyed at loop end.

        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 sitesv
          #70

          @JonB @KroMignon
          Agree with you, guys.
          But it works...
          I can reimplement to QProcess pointers of PingTester class...

          KroMignonK 1 Reply Last reply
          0
          • sitesvS sitesv

            @JonB @KroMignon
            Agree with you, guys.
            But it works...
            I can reimplement to QProcess pointers of PingTester class...

            KroMignonK Offline
            KroMignonK Offline
            KroMignon
            wrote on last edited by
            #71

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

            But it works...

            It don't, "it seems to work" would be the correct answer ;)

            If you try to ping a not valid/accessible IP address, I am pretty sure it will not work.

            If you want to do it sequentially, you have to be consistent in your choice:

            foreach(auto ip, ip_list)
            {
                QProcess ping;
                ping.setProcessChannelMode(QProcess::MergedChannels);
                ping.start("/bin/ping", QStringList() << ip << "-c" << "1" << "-w" << "1");
                ping.waitForFinished(5000); // wait up to 5 seconds
                QString output(ping.readAll());
                if(output.contains("ttl",Qt::CaseInsensitive)){
                    success_count++;
                }
            }
            

            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 JonBJ 2 Replies Last reply
            0
            • KroMignonK KroMignon

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

              But it works...

              It don't, "it seems to work" would be the correct answer ;)

              If you try to ping a not valid/accessible IP address, I am pretty sure it will not work.

              If you want to do it sequentially, you have to be consistent in your choice:

              foreach(auto ip, ip_list)
              {
                  QProcess ping;
                  ping.setProcessChannelMode(QProcess::MergedChannels);
                  ping.start("/bin/ping", QStringList() << ip << "-c" << "1" << "-w" << "1");
                  ping.waitForFinished(5000); // wait up to 5 seconds
                  QString output(ping.readAll());
                  if(output.contains("ttl",Qt::CaseInsensitive)){
                      success_count++;
                  }
              }
              
              sitesvS Offline
              sitesvS Offline
              sitesv
              wrote on last edited by
              #72

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

              If you try to ping a not valid/accessible IP address, I am pretty sure it will not work.

              There is "-w 1" key. It helps with unaccessible IP.

              KroMignonK 1 Reply Last reply
              0
              • KroMignonK KroMignon

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

                But it works...

                It don't, "it seems to work" would be the correct answer ;)

                If you try to ping a not valid/accessible IP address, I am pretty sure it will not work.

                If you want to do it sequentially, you have to be consistent in your choice:

                foreach(auto ip, ip_list)
                {
                    QProcess ping;
                    ping.setProcessChannelMode(QProcess::MergedChannels);
                    ping.start("/bin/ping", QStringList() << ip << "-c" << "1" << "-w" << "1");
                    ping.waitForFinished(5000); // wait up to 5 seconds
                    QString output(ping.readAll());
                    if(output.contains("ttl",Qt::CaseInsensitive)){
                        success_count++;
                    }
                }
                
                JonBJ Offline
                JonBJ Offline
                JonB
                wrote on last edited by JonB
                #73

                @KroMignon
                I would think doing it sequentially, with waitForFinished(), for his multiple IP addresses would be a poor way to do things. He has a number of IP addresses to check, these should be done in parallel....

                1 Reply Last reply
                0
                • sitesvS sitesv

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

                  If you try to ping a not valid/accessible IP address, I am pretty sure it will not work.

                  There is "-w 1" key. It helps with unaccessible IP.

                  KroMignonK Offline
                  KroMignonK Offline
                  KroMignon
                  wrote on last edited by
                  #74

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

                  There is "-w 1" key. It helps with unaccessible IP.

                  AFAIK "-w 1" will wait up to 1 second.
                  I am sure you will got QProcess warnings about killing a process which is still running.

                  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 "-w 1" key. It helps with unaccessible IP.

                    AFAIK "-w 1" will wait up to 1 second.
                    I am sure you will got QProcess warnings about killing a process which is still running.

                    sitesvS Offline
                    sitesvS Offline
                    sitesv
                    wrote on last edited by sitesv
                    #75

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

                    AFAIK "-w 1" will wait up to 1 second.

                    ...and QProcess will emit a "finished" signal. Why you are writing about "killing" process?

                    KroMignonK 1 Reply Last reply
                    0
                    • sitesvS sitesv

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

                      AFAIK "-w 1" will wait up to 1 second.

                      ...and QProcess will emit a "finished" signal. Why you are writing about "killing" process?

                      KroMignonK Offline
                      KroMignonK Offline
                      KroMignon
                      wrote on last edited by KroMignon
                      #76

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

                      ...and QProcess will emit a "finished" signal. Why you are writing about "killing" process?

                      This is the way I would implement multiple pings in parallel:

                      int PingTester::doPing(const QStringList &ip_list)
                      {
                          // to avoid issues ;)
                          if(ip_list.isEmpty())
                              return 0;
                      
                          int success_count = 0;
                          int pingsToDo = ip_list.count();
                          QEventLoop l;
                          QTimer timer;
                          foreach(auto ip, ip_list)
                          {
                              auto ping = new QProcess();
                              ping->setProcessChannelMode(QProcess::MergedChannels);
                              connect(timer, &QTimer::timeout, ping, &QProcess::kill);
                              connect(ping, &QProcess::stateChanged,
                                      [&l, ping, &success_count, &pingsToDo](QProcess::ProcessState newState) {
                                          if(newState != QProcess::NotRunning)
                                              return;
                                          --pingsToDo;
                                          QString output(ping->readAll());
                                          if(output.contains("ttl",Qt::CaseInsensitive))
                                              success_count++;
                                          // free memory
                                          ping->deleteLater();
                                          // exit loop when done.
                                          if(!pingsToDo)
                                              l.exit();
                                      });
                              ping->start("/bin/ping", QStringList() << ip << "-c" << "1" << "-w" << "1");
                          }
                          timer.start(1500); // kill process after 1.5 seconds if still running
                          // wait all pings done
                          l.exec();
                          return success_count;
                      }
                      

                      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
                      • sitesvS Offline
                        sitesvS Offline
                        sitesv
                        wrote on last edited by sitesv
                        #77

                        @jsulm There is a local QEventLoop...
                        @KroMignon I really don't understand why you are checking state changing of QProcess...
                        QProcess "Finished" method is not suitable?
                        And why kill a process?

                        KroMignonK 1 Reply Last reply
                        0
                        • sitesvS sitesv

                          @jsulm There is a local QEventLoop...
                          @KroMignon I really don't understand why you are checking state changing of QProcess...
                          QProcess "Finished" method is not suitable?
                          And why kill a process?

                          KroMignonK Offline
                          KroMignonK Offline
                          KroMignon
                          wrote on last edited by KroMignon
                          #78

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

                          QProcess "Finished" method is not suitable?

                          I found it easier to use QProcess::stateChanged(), because there is no overload of this slot, and I am not sure if QProcess::finished(int, QProcess::ExitStatus) is triggered if process is killed.

                          And why kill a process?

                          This is a security, when calling an external application, many things can happen: execution right issues, application not exist, network issues and so on.
                          99.9% of time it will not be useful, but it will ensure QEventLoop will exit at the end!

                          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
                          • KroMignonK KroMignon

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

                            ...and QProcess will emit a "finished" signal. Why you are writing about "killing" process?

                            This is the way I would implement multiple pings in parallel:

                            int PingTester::doPing(const QStringList &ip_list)
                            {
                                // to avoid issues ;)
                                if(ip_list.isEmpty())
                                    return 0;
                            
                                int success_count = 0;
                                int pingsToDo = ip_list.count();
                                QEventLoop l;
                                QTimer timer;
                                foreach(auto ip, ip_list)
                                {
                                    auto ping = new QProcess();
                                    ping->setProcessChannelMode(QProcess::MergedChannels);
                                    connect(timer, &QTimer::timeout, ping, &QProcess::kill);
                                    connect(ping, &QProcess::stateChanged,
                                            [&l, ping, &success_count, &pingsToDo](QProcess::ProcessState newState) {
                                                if(newState != QProcess::NotRunning)
                                                    return;
                                                --pingsToDo;
                                                QString output(ping->readAll());
                                                if(output.contains("ttl",Qt::CaseInsensitive))
                                                    success_count++;
                                                // free memory
                                                ping->deleteLater();
                                                // exit loop when done.
                                                if(!pingsToDo)
                                                    l.exit();
                                            });
                                    ping->start("/bin/ping", QStringList() << ip << "-c" << "1" << "-w" << "1");
                                }
                                timer.start(1500); // kill process after 1.5 seconds if still running
                                // wait all pings done
                                l.exec();
                                return success_count;
                            }
                            
                            sitesvS Offline
                            sitesvS Offline
                            sitesv
                            wrote on last edited by sitesv
                            #79

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

                            This is the way I would implement multiple pings in parallel:

                            This code doesn't work. Only one iteration.

                            1 Reply Last reply
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