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Executing QProcess in QThread: memory leak

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  • Christian EhrlicherC Christian Ehrlicher

    @sitesv A system monitor is not a valid tool for such an investigation. It may be a hint that there is something wrong but nothing more. The system monitor only shows what the OS gave the process, but the OS may not free resources immediately but only when it needs it later on so use a correct tool for this.

    sitesvS Offline
    sitesvS Offline
    sitesv
    wrote on last edited by
    #13

    @Christian-Ehrlicher
    Checked app by Valgrind. There is no memory leak...
    Thank you. I hope there really are no errors.

    mrjjM 1 Reply Last reply
    2
    • sitesvS sitesv

      @Christian-Ehrlicher
      Checked app by Valgrind. There is no memory leak...
      Thank you. I hope there really are no errors.

      mrjjM Offline
      mrjjM Offline
      mrjj
      Lifetime Qt Champion
      wrote on last edited by
      #14

      @sitesv
      I would leave it running for like 48 hours and see it would stabilize.
      If its related to actually running the process on Os level, it might only allocate up to some max.

      sitesvS 1 Reply Last reply
      1
      • Christian EhrlicherC Offline
        Christian EhrlicherC Offline
        Christian Ehrlicher
        Lifetime Qt Champion
        wrote on last edited by
        #15

        Since Qt cleans up a lot of stuff during exit maybe also stop the application started with valgrind with CTRL+C and take a look at the reachable memory in the valgrind output to see if there is something interesting (start valgrind with '--show-reachable=yes')

        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
        3
        • mrjjM mrjj

          @sitesv
          I would leave it running for like 48 hours and see it would stabilize.
          If its related to actually running the process on Os level, it might only allocate up to some max.

          sitesvS Offline
          sitesvS Offline
          sitesv
          wrote on last edited by
          #16

          @mrjj, @Christian-Ehrlicher
          Thank you!

          1 Reply Last reply
          0
          • sitesvS Offline
            sitesvS Offline
            sitesv
            wrote on last edited by sitesv
            #17

            Hi!
            Made a simple test:

            void mythread::run(){
                while(work){
                    bool boolRESULT;
                    QString output_str;
                    QByteArray output;
                    QStringList output_strlst;
                    QTextCodec *codec;
                    QString exe_path = "/bin/ping";;
                    QStringList arguments;
                    arguments << "127.0.0.1" << "-c" << "1";
            
                    if(myProcess == nullptr) myProcess = new QProcess;
                    myProcess->start(exe_path, arguments);
                    myProcess->waitForFinished(500);
            
                    output = myProcess->readAll();
                    output_str = codec->toUnicode(output);
                    output_strlst = output_str.split("\r\n");
            
                    myProcess->close();
                     
                    boolRESULT = false;
                    for (int i = 0; i < output_strlst.count(); i++){
                        boolRESULT = output_strlst[i].contains("ttl",Qt::CaseInsensitive);
                        if (boolRESULT) break;
                    }
                    emit setStatus(boolRESULT);
               
                    msleep(1000);
                }
            }
            

            Valgrind output:
            ...
            ==23633== 2,400 bytes in 15 blocks are still reachable in loss record 2,049 of 2,114
            ==23633== at 0x4C2BBEF: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
            ==23633== by 0x6267251: resizeSignalVector (qobject_p.h:297)
            ==23633== by 0x6267251: QObjectPrivate::addConnection(int, QObjectPrivate::Connection*) (qobject.cpp:330)
            ==23633== by 0x6268A18: QMetaObjectPrivate::connect(QObject const*, int, QMetaObject const*, QObject const*, int, QMetaObject const*, int, int*) (qobject.cpp:3453)
            ==23633== by 0x626FD58: QObject::connect(QObject const*, char const*, QObject const*, char const*, Qt::ConnectionType) (qobject.cpp:2911)
            ==23633== by 0x61BFB1F: QProcessPrivate::startProcess() (qprocess_unix.cpp:384)
            ==23633== by 0x61BA34D: QProcessPrivate::start(QFlagsQIODevice::OpenModeFlag) (qprocess.cpp:2246)
            ==23633== by 0x61BA582: QProcess::start(QString const&, QStringList const&, QFlagsQIODevice::OpenModeFlag) (qprocess.cpp:2094)
            ==23633== by 0x10BBBF: mythread::run() (mythread.cpp:19)

            ==23633== by 0x605A3B4: QThreadPrivate::start(void*) (qthread_unix.cpp:342)
            ==23633== by 0x6A164A3: start_thread (pthread_create.c:456)
            ==23633== by 0x75B1D0E: clone (clone.S:97)
            ...

            mythread.cpp 19 line is:

            myProcess->start(exe_path, arguments);
            

            My log by system monitor:

            • 16:50 4300 KB
            • 17:06 4790 KB
            • 17:20 5200 KB
            • 17:30 5552 KB

            Any ideas?

            KroMignonK JonBJ 2 Replies Last reply
            0
            • sitesvS sitesv

              Hi!
              Made a simple test:

              void mythread::run(){
                  while(work){
                      bool boolRESULT;
                      QString output_str;
                      QByteArray output;
                      QStringList output_strlst;
                      QTextCodec *codec;
                      QString exe_path = "/bin/ping";;
                      QStringList arguments;
                      arguments << "127.0.0.1" << "-c" << "1";
              
                      if(myProcess == nullptr) myProcess = new QProcess;
                      myProcess->start(exe_path, arguments);
                      myProcess->waitForFinished(500);
              
                      output = myProcess->readAll();
                      output_str = codec->toUnicode(output);
                      output_strlst = output_str.split("\r\n");
              
                      myProcess->close();
                       
                      boolRESULT = false;
                      for (int i = 0; i < output_strlst.count(); i++){
                          boolRESULT = output_strlst[i].contains("ttl",Qt::CaseInsensitive);
                          if (boolRESULT) break;
                      }
                      emit setStatus(boolRESULT);
                 
                      msleep(1000);
                  }
              }
              

              Valgrind output:
              ...
              ==23633== 2,400 bytes in 15 blocks are still reachable in loss record 2,049 of 2,114
              ==23633== at 0x4C2BBEF: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
              ==23633== by 0x6267251: resizeSignalVector (qobject_p.h:297)
              ==23633== by 0x6267251: QObjectPrivate::addConnection(int, QObjectPrivate::Connection*) (qobject.cpp:330)
              ==23633== by 0x6268A18: QMetaObjectPrivate::connect(QObject const*, int, QMetaObject const*, QObject const*, int, QMetaObject const*, int, int*) (qobject.cpp:3453)
              ==23633== by 0x626FD58: QObject::connect(QObject const*, char const*, QObject const*, char const*, Qt::ConnectionType) (qobject.cpp:2911)
              ==23633== by 0x61BFB1F: QProcessPrivate::startProcess() (qprocess_unix.cpp:384)
              ==23633== by 0x61BA34D: QProcessPrivate::start(QFlagsQIODevice::OpenModeFlag) (qprocess.cpp:2246)
              ==23633== by 0x61BA582: QProcess::start(QString const&, QStringList const&, QFlagsQIODevice::OpenModeFlag) (qprocess.cpp:2094)
              ==23633== by 0x10BBBF: mythread::run() (mythread.cpp:19)

              ==23633== by 0x605A3B4: QThreadPrivate::start(void*) (qthread_unix.cpp:342)
              ==23633== by 0x6A164A3: start_thread (pthread_create.c:456)
              ==23633== by 0x75B1D0E: clone (clone.S:97)
              ...

              mythread.cpp 19 line is:

              myProcess->start(exe_path, arguments);
              

              My log by system monitor:

              • 16:50 4300 KB
              • 17:06 4790 KB
              • 17:20 5200 KB
              • 17:30 5552 KB

              Any ideas?

              KroMignonK Offline
              KroMignonK Offline
              KroMignon
              wrote on last edited by KroMignon
              #18

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

              Made a simple test:

              You are aware that doing so (subclassing QThread and redefining slot run()), there will be not QEventLoop to handle signals/slots for all QObjects running in this thread?
              For example QTimer::singleShot() will not work.

              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

                Hi!
                Made a simple test:

                void mythread::run(){
                    while(work){
                        bool boolRESULT;
                        QString output_str;
                        QByteArray output;
                        QStringList output_strlst;
                        QTextCodec *codec;
                        QString exe_path = "/bin/ping";;
                        QStringList arguments;
                        arguments << "127.0.0.1" << "-c" << "1";
                
                        if(myProcess == nullptr) myProcess = new QProcess;
                        myProcess->start(exe_path, arguments);
                        myProcess->waitForFinished(500);
                
                        output = myProcess->readAll();
                        output_str = codec->toUnicode(output);
                        output_strlst = output_str.split("\r\n");
                
                        myProcess->close();
                         
                        boolRESULT = false;
                        for (int i = 0; i < output_strlst.count(); i++){
                            boolRESULT = output_strlst[i].contains("ttl",Qt::CaseInsensitive);
                            if (boolRESULT) break;
                        }
                        emit setStatus(boolRESULT);
                   
                        msleep(1000);
                    }
                }
                

                Valgrind output:
                ...
                ==23633== 2,400 bytes in 15 blocks are still reachable in loss record 2,049 of 2,114
                ==23633== at 0x4C2BBEF: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
                ==23633== by 0x6267251: resizeSignalVector (qobject_p.h:297)
                ==23633== by 0x6267251: QObjectPrivate::addConnection(int, QObjectPrivate::Connection*) (qobject.cpp:330)
                ==23633== by 0x6268A18: QMetaObjectPrivate::connect(QObject const*, int, QMetaObject const*, QObject const*, int, QMetaObject const*, int, int*) (qobject.cpp:3453)
                ==23633== by 0x626FD58: QObject::connect(QObject const*, char const*, QObject const*, char const*, Qt::ConnectionType) (qobject.cpp:2911)
                ==23633== by 0x61BFB1F: QProcessPrivate::startProcess() (qprocess_unix.cpp:384)
                ==23633== by 0x61BA34D: QProcessPrivate::start(QFlagsQIODevice::OpenModeFlag) (qprocess.cpp:2246)
                ==23633== by 0x61BA582: QProcess::start(QString const&, QStringList const&, QFlagsQIODevice::OpenModeFlag) (qprocess.cpp:2094)
                ==23633== by 0x10BBBF: mythread::run() (mythread.cpp:19)

                ==23633== by 0x605A3B4: QThreadPrivate::start(void*) (qthread_unix.cpp:342)
                ==23633== by 0x6A164A3: start_thread (pthread_create.c:456)
                ==23633== by 0x75B1D0E: clone (clone.S:97)
                ...

                mythread.cpp 19 line is:

                myProcess->start(exe_path, arguments);
                

                My log by system monitor:

                • 16:50 4300 KB
                • 17:06 4790 KB
                • 17:20 5200 KB
                • 17:30 5552 KB

                Any ideas?

                JonBJ Offline
                JonBJ Offline
                JonB
                wrote on last edited by JonB
                #19

                @sitesv
                In addition, from @KroMignon no QEventLoop also means no deleting/disposing/freeing of Qt objects.

                On a side note: nothing to do with your findings, but for the record

                 arguments << "127.0.0.1" << "-c 1";
                

                is wrong: -c & 1 are separate arguments, it ought to be << "-c" << "1". You are lucky it works as one argument.

                sitesvS 1 Reply Last reply
                1
                • sitesvS Offline
                  sitesvS Offline
                  sitesv
                  wrote on last edited by
                  #20

                  @KroMignon @JonB
                  Are there any methods to do this correctly?
                  If I do this in the main thread: the app will freeze while QProcess execution - this is unacceptable for me.

                  KroMignonK 1 Reply Last reply
                  0
                  • sitesvS sitesv

                    @KroMignon @JonB
                    Are there any methods to do this correctly?
                    If I do this in the main thread: the app will freeze while QProcess execution - this is unacceptable for me.

                    KroMignonK Offline
                    KroMignonK Offline
                    KroMignon
                    wrote on last edited by
                    #21

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

                    Are there any methods to do this correctly?

                    I don't say this is incorrect.
                    I depends what you want to achieve.
                    If you don't need an event queue, it works. If you are using signals/slots, this will not work.

                    I do not know what is the purpose of this code extract, so maybe it is the best way to do.

                    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:

                      Are there any methods to do this correctly?

                      I don't say this is incorrect.
                      I depends what you want to achieve.
                      If you don't need an event queue, it works. If you are using signals/slots, this will not work.

                      I do not know what is the purpose of this code extract, so maybe it is the best way to do.

                      sitesvS Offline
                      sitesvS Offline
                      sitesv
                      wrote on last edited by
                      #22

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

                      If you don't need an event queue, it works. If you are using signals/slots, this will not work.

                      I don't know, but from this qthread in my main app I emit signal... and it is emitted... slot is from the main thread. QThread starts by start() method.
                      The problem for me is memory leak only.

                      KroMignonK 1 Reply Last reply
                      0
                      • JonBJ JonB

                        @sitesv
                        In addition, from @KroMignon no QEventLoop also means no deleting/disposing/freeing of Qt objects.

                        On a side note: nothing to do with your findings, but for the record

                         arguments << "127.0.0.1" << "-c 1";
                        

                        is wrong: -c & 1 are separate arguments, it ought to be << "-c" << "1". You are lucky it works as one argument.

                        sitesvS Offline
                        sitesvS Offline
                        sitesv
                        wrote on last edited by
                        #23

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

                        In addition, from @KroMignon no QEventLoop also means no deleting/disposing/freeing of Qt objects.

                        QCoreApplication::processEvents would help?

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

                        is wrong: -c & 1 are separate arguments, it ought to be << "-c" << "1". You are lucky it works as one argument.

                        Thank you! Fixed.

                        1 Reply Last reply
                        0
                        • sitesvS sitesv

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

                          If you don't need an event queue, it works. If you are using signals/slots, this will not work.

                          I don't know, but from this qthread in my main app I emit signal... and it is emitted... slot is from the main thread. QThread starts by start() method.
                          The problem for me is memory leak only.

                          KroMignonK Offline
                          KroMignonK Offline
                          KroMignon
                          wrote on last edited by
                          #24

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

                          I don't know, but from this qthread in my main app I emit signal... and it is emitted... slot is from the main thread. QThread starts by start() method.
                          The problem for me is memory leak only.

                          For my comprehension of QObject and QThread (cf Threads and QObjects), your implementation is not really Qt friendly.

                          If I right understand what you want to achieve: you want to run "ping" a regular interval and be informed when ping has failed.

                          To do this, I would create a QObject class which handles the ping requests and eventually moves this class instance to a dedicated thread to avoid lock on main thread.

                          Something like:

                          class PingTester : public QObject
                          {
                              Q_OBJECT
                          
                          public:
                              explicit PingTester(QObject* parent = nullptr): QObject(parent), m_timer(new QTimer(this))
                              {
                                  m_timer->setInterval(30*1000); // per default 30 seconds
                                  m_timer->setSingleShot(false);
                                  connect(m_timer, &QTimer::timeout, this, &PingTester::doPing);
                              }
                          
                              void setInterval(int interval) { m_timer->setInterval(interval); }
                          
                          public slots:
                               void start()
                               {
                                   if(QThread::currentThrea() != thread())
                                   {
                                        QTimer::singleShot(this, 0, &PingTester::start);
                                        return;
                                   }
                                   if(!m_timer->isActive())
                                       m_timer->start();
                               }
                               void stop()
                               {
                                   if(QThread::currentThrea() != thread())
                                   {
                                        QTimer::singleShot(this, 0, &PingTester::stop);
                                        return;
                                   }
                                   if(m_timer->isActive())
                                       m_timer->stop();
                               }
                               
                          private slots:
                              void doPing();
                          
                          signals:
                              void pingFailure();
                              void pingSuccess();
                          
                          private:
                               QTimer* m_timer;
                          };
                          

                          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
                          • SGaistS Offline
                            SGaistS Offline
                            SGaist
                            Lifetime Qt Champion
                            wrote on last edited by
                            #25

                            Hi,

                            Can you explain why exactly do you need that ping ?

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

                            1 Reply Last reply
                            1
                            • sitesvS Offline
                              sitesvS Offline
                              sitesv
                              wrote on last edited by
                              #26

                              @SGaist
                              ping needs to check the availability of pc from the internal network. I thought that this is the simplest way to do this.

                              1 Reply Last reply
                              0
                              • Christian EhrlicherC Offline
                                Christian EhrlicherC Offline
                                Christian Ehrlicher
                                Lifetime Qt Champion
                                wrote on last edited by
                                #27

                                But why a thread then?

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                                sitesvS 1 Reply Last reply
                                1
                                • sitesvS Offline
                                  sitesvS Offline
                                  sitesv
                                  wrote on last edited by sitesv
                                  #28

                                  @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 1 Reply Last reply
                                  0
                                  • Christian EhrlicherC Christian Ehrlicher

                                    But why a thread then?

                                    sitesvS Offline
                                    sitesvS Offline
                                    sitesv
                                    wrote on last edited by
                                    #29

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

                                    But why a thread then?

                                    I need to check availability constantly during the program. I thought the QThread is a good way to do this...

                                    1 Reply Last reply
                                    0
                                    • Christian EhrlicherC Offline
                                      Christian EhrlicherC Offline
                                      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/
                                      Visit the Qt Academy at https://academy.qt.io/catalog

                                      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 Offline
                                          Christian EhrlicherC Offline
                                          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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