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Executing QProcess in QThread: memory leak

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  • mrjjM mrjj

    Hi
    How do you know there is a leak ?

    sitesvS Offline
    sitesvS Offline
    sitesv
    wrote on last edited by
    #3

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

    Hi
    How do you know there is a leak ?

    By system monitor...
    A leak is about 4k/sec. I have been checking for a few minutes...

    mrjjM Christian EhrlicherC 2 Replies Last reply
    0
    • sitesvS sitesv

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

      Hi
      How do you know there is a leak ?

      By system monitor...
      A leak is about 4k/sec. I have been checking for a few minutes...

      mrjjM Offline
      mrjjM Offline
      mrjj
      Lifetime Qt Champion
      wrote on last edited by
      #4

      @sitesv
      Ok. it might internally allocate something
      that is first freed on app termination.

      If you reuse the same QProcess
      (let it be a member of the TMyThread, allocate once)

      Does it still then still leak ?

      sitesvS 1 Reply Last reply
      0
      • mrjjM mrjj

        @sitesv
        Ok. it might internally allocate something
        that is first freed on app termination.

        If you reuse the same QProcess
        (let it be a member of the TMyThread, allocate once)

        Does it still then still leak ?

        sitesvS Offline
        sitesvS Offline
        sitesv
        wrote on last edited by
        #5

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

        Does it still then still leak ?

        Yes, there is still a leak.
        QProcess myProcess; moved into the class.

        sitesvS 1 Reply Last reply
        0
        • sitesvS sitesv

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

          Does it still then still leak ?

          Yes, there is still a leak.
          QProcess myProcess; moved into the class.

          sitesvS Offline
          sitesvS Offline
          sitesv
          wrote on last edited by
          #6

          @mrjj
          If I would use this code in while(1) of the 'main' function of the console app - there is NO memory leak.

          mrjjM 1 Reply Last reply
          0
          • sitesvS sitesv

            @mrjj
            If I would use this code in while(1) of the 'main' function of the console app - there is NO memory leak.

            mrjjM Offline
            mrjjM Offline
            mrjj
            Lifetime Qt Champion
            wrote on last edited by
            #7

            @sitesv
            but you only create the thread once , so it should be the same ?

            sitesvS 1 Reply Last reply
            0
            • mrjjM mrjj

              @sitesv
              but you only create the thread once , so it should be the same ?

              sitesvS Offline
              sitesvS Offline
              sitesv
              wrote on last edited by
              #8

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

              but you only create the thread once ,

              Yes.

              1 Reply Last reply
              0
              • mrjjM Offline
                mrjjM Offline
                mrjj
                Lifetime Qt Champion
                wrote on last edited by
                #9

                Hi
                Hmm really strange then.
                Is this on windows ?
                I did something similar on linux and didnt notice it would leak 4K

                sitesvS 1 Reply Last reply
                0
                • sitesvS sitesv

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

                  Hi
                  How do you know there is a leak ?

                  By system monitor...
                  A leak is about 4k/sec. I have been checking for a few minutes...

                  Christian EhrlicherC Offline
                  Christian EhrlicherC Offline
                  Christian Ehrlicher
                  Lifetime Qt Champion
                  wrote on last edited by
                  #10

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

                  By system monitor...

                  This is no valid memory leak checker. Use a correct to to find leaks like e.g. valgrind.

                  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
                  2
                  • mrjjM mrjj

                    Hi
                    Hmm really strange then.
                    Is this on windows ?
                    I did something similar on linux and didnt notice it would leak 4K

                    sitesvS Offline
                    sitesvS Offline
                    sitesv
                    wrote on last edited by
                    #11

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

                    Is this on windows ?

                    Linux

                    @Christian-Ehrlicher
                    Is it correct, If a memory value is increasing for a few minutes?

                    Christian EhrlicherC 1 Reply Last reply
                    0
                    • sitesvS sitesv

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

                      Is this on windows ?

                      Linux

                      @Christian-Ehrlicher
                      Is it correct, If a memory value is increasing for a few minutes?

                      Christian EhrlicherC Offline
                      Christian EhrlicherC Offline
                      Christian Ehrlicher
                      Lifetime Qt Champion
                      wrote on last edited by
                      #12

                      @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.

                      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

                        @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
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