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QProgressbar unresponsive with qthread

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  • M meganathan

    @J.Hilk

    I tried like this
    QEventLoop loop;
    ansysThread->start();
    loop.exec();
    connect(ansysThread, SIGNAL(finished()),this,SLOT(onQProcessFinish()));

    finished() signal emits before Qthread::run() completes the execution. Hot to approach this, if i use ansysthread->wait() it blocks the main GUI thread.. So please suggest any other suggestion.

    jsulmJ Offline
    jsulmJ Offline
    jsulm
    Lifetime Qt Champion
    wrote on last edited by
    #11

    @meganathan said in QProgressbar unresponsive with qthread:

    QEventLoop loop;
    ansysThread->start();
    loop.exec();
    connect(ansysThread, SIGNAL(finished()),this,SLOT(onQProcessFinish()));

    Why do you block your thread with

    loop.exec();
    

    ?!
    It should be

    connect(ansysThread, SIGNAL(finished()),this,SLOT(onQProcessFinish()));
    ansysThread->start();
    

    https://forum.qt.io/topic/113070/qt-code-of-conduct

    M 1 Reply Last reply
    1
    • jsulmJ jsulm

      @meganathan said in QProgressbar unresponsive with qthread:

      QEventLoop loop;
      ansysThread->start();
      loop.exec();
      connect(ansysThread, SIGNAL(finished()),this,SLOT(onQProcessFinish()));

      Why do you block your thread with

      loop.exec();
      

      ?!
      It should be

      connect(ansysThread, SIGNAL(finished()),this,SLOT(onQProcessFinish()));
      ansysThread->start();
      
      M Offline
      M Offline
      meganathan
      wrote on last edited by
      #12

      @jsulm

      I need to wait for thread to completed the process..how can i approach without using ansysthread->wait()

      jsulmJ 1 Reply Last reply
      0
      • M meganathan

        @jsulm

        I need to wait for thread to completed the process..how can i approach without using ansysthread->wait()

        jsulmJ Offline
        jsulmJ Offline
        jsulm
        Lifetime Qt Champion
        wrote on last edited by jsulm
        #13

        @meganathan Why do you need to wait? If you wait you block the waiting thread - and then you complain that the thread is blocking and progress bar not updating?! And if you want to wait then what is the point to use threads?
        You get the finished() signal when it is finished and can do whatever needs to be done when the thread finishes.
        Qt is asynchronous and you should avoid waiting for something. Learn how to program in an asynchronous way else there is no point to use Qt or threads.

        https://forum.qt.io/topic/113070/qt-code-of-conduct

        M 1 Reply Last reply
        0
        • jsulmJ jsulm

          @meganathan Why do you need to wait? If you wait you block the waiting thread - and then you complain that the thread is blocking and progress bar not updating?! And if you want to wait then what is the point to use threads?
          You get the finished() signal when it is finished and can do whatever needs to be done when the thread finishes.
          Qt is asynchronous and you should avoid waiting for something. Learn how to program in an asynchronous way else there is no point to use Qt or threads.

          M Offline
          M Offline
          meganathan
          wrote on last edited by
          #14

          @jsulm
          Based of the files generated by script inside ansysthread, i need to proceed after the script completes execution. i am struct there without using ansysthread->wait()

          jsulmJ 1 Reply Last reply
          0
          • M meganathan

            @jsulm
            Based of the files generated by script inside ansysthread, i need to proceed after the script completes execution. i am struct there without using ansysthread->wait()

            jsulmJ Offline
            jsulmJ Offline
            jsulm
            Lifetime Qt Champion
            wrote on last edited by
            #15

            @meganathan Again: you know when the thread finishes - you get the finished() signal. So, why don't you simply connect a slot to that signal and process in that slot?

            https://forum.qt.io/topic/113070/qt-code-of-conduct

            M 1 Reply Last reply
            0
            • jsulmJ jsulm

              @meganathan Again: you know when the thread finishes - you get the finished() signal. So, why don't you simply connect a slot to that signal and process in that slot?

              M Offline
              M Offline
              meganathan
              wrote on last edited by
              #16

              @jsulm
              By the time thread emits finished() signal, all my remaining things that to done(after script execution) are already executed. This makes no sense. By using QEventloop can we block the until thread emits finished() signal.?

              J.HilkJ jsulmJ 2 Replies Last reply
              0
              • M meganathan

                @jsulm
                By the time thread emits finished() signal, all my remaining things that to done(after script execution) are already executed. This makes no sense. By using QEventloop can we block the until thread emits finished() signal.?

                J.HilkJ Offline
                J.HilkJ Offline
                J.Hilk
                Moderators
                wrote on last edited by
                #17

                @meganathan as a rule of thumb,

                if you're using QEventLoop or QProcessEvents, you're doing something wrong(95% chance).


                Be aware of the Qt Code of Conduct, when posting : https://forum.qt.io/topic/113070/qt-code-of-conduct


                Q: What's that?
                A: It's blue light.
                Q: What does it do?
                A: It turns blue.

                1 Reply Last reply
                2
                • M meganathan

                  @jsulm
                  By the time thread emits finished() signal, all my remaining things that to done(after script execution) are already executed. This makes no sense. By using QEventloop can we block the until thread emits finished() signal.?

                  jsulmJ Offline
                  jsulmJ Offline
                  jsulm
                  Lifetime Qt Champion
                  wrote on last edited by
                  #18

                  @meganathan said in QProgressbar unresponsive with qthread:

                  all my remaining things that to done(after script execution) are already executed

                  Then do all these things in the slot connected to finished() signal as I already suggested.
                  "By using QEventloop can we block the until thread emits finished() signal.?" - you can, but then your progress bar will not update which was your first question in this thread, right? And if you anyway want to block, then why do you want to use threads? I don't see the point...

                  https://forum.qt.io/topic/113070/qt-code-of-conduct

                  M 1 Reply Last reply
                  0
                  • J.HilkJ Offline
                    J.HilkJ Offline
                    J.Hilk
                    Moderators
                    wrote on last edited by
                    #19

                    here:

                    #ifndef SUBTHREAD_H
                    #define SUBTHREAD_H
                    
                    #include <QObject>
                    #include <QThread>
                    
                    class SubThread : public QThread
                    {
                        Q_OBJECT
                    public:
                        explicit SubThread(QObject *parent = nullptr);
                    
                    protected:
                        virtual void run()override;
                    
                    signals:
                        void status(int stat);
                    
                    public slots:
                    };
                    
                    #endif // SUBTHREAD_H
                    
                    
                    #include "subthread.h"
                    #include <QTime>
                    
                    SubThread::SubThread(QObject *parent) : QThread(parent)
                    {
                    
                    }
                    
                    void SubThread::run()
                    {
                        QTime t;
                        t.start();
                    
                        while(t.elapsed() < 10000){
                            if(t.elapsed() % 100 == 0)
                                emit status(t.elapsed()/100);
                        }
                    }
                    
                    #include <QApplication>
                    #include <QProgressBar>
                    #include "subthread.h"
                    
                    int main(int argc, char *argv[])
                    {
                        QApplication a(argc, argv);
                    
                        QProgressBar bar;
                        bar.show();
                    
                        SubThread myThread;
                    
                        QObject::connect(&myThread, &SubThread::status, &bar, &QProgressBar::setValue);
                        QObject::connect(&myThread, &SubThread::finished, &a, &QApplication::quit);
                        myThread.start();
                    
                    
                        return  a.exec();
                    }
                    

                    Be aware of the Qt Code of Conduct, when posting : https://forum.qt.io/topic/113070/qt-code-of-conduct


                    Q: What's that?
                    A: It's blue light.
                    Q: What does it do?
                    A: It turns blue.

                    JonBJ 1 Reply Last reply
                    1
                    • J.HilkJ J.Hilk

                      here:

                      #ifndef SUBTHREAD_H
                      #define SUBTHREAD_H
                      
                      #include <QObject>
                      #include <QThread>
                      
                      class SubThread : public QThread
                      {
                          Q_OBJECT
                      public:
                          explicit SubThread(QObject *parent = nullptr);
                      
                      protected:
                          virtual void run()override;
                      
                      signals:
                          void status(int stat);
                      
                      public slots:
                      };
                      
                      #endif // SUBTHREAD_H
                      
                      
                      #include "subthread.h"
                      #include <QTime>
                      
                      SubThread::SubThread(QObject *parent) : QThread(parent)
                      {
                      
                      }
                      
                      void SubThread::run()
                      {
                          QTime t;
                          t.start();
                      
                          while(t.elapsed() < 10000){
                              if(t.elapsed() % 100 == 0)
                                  emit status(t.elapsed()/100);
                          }
                      }
                      
                      #include <QApplication>
                      #include <QProgressBar>
                      #include "subthread.h"
                      
                      int main(int argc, char *argv[])
                      {
                          QApplication a(argc, argv);
                      
                          QProgressBar bar;
                          bar.show();
                      
                          SubThread myThread;
                      
                          QObject::connect(&myThread, &SubThread::status, &bar, &QProgressBar::setValue);
                          QObject::connect(&myThread, &SubThread::finished, &a, &QApplication::quit);
                          myThread.start();
                      
                      
                          return  a.exec();
                      }
                      
                      JonBJ Offline
                      JonBJ Offline
                      JonB
                      wrote on last edited by
                      #20

                      @J.Hilk

                        while(t.elapsed() < 10000){
                      

                      Now, you doubtless know more than I about threads, because I don't use them. But I don't get this approach. It looks like you're spinning an awfully busy loop. It's true than your main thread will run uninterrupted, but half the CPU will be executing this all the time/your mobile battery is going to drain, no? Could you explain?

                      This is why the OP is asking about QEventLoop etc. Does a QThread run its own event loop? Does it exit when it gets to end of run() or does it have to be terminated explicitly?

                      jsulmJ J.HilkJ 2 Replies Last reply
                      0
                      • JonBJ JonB

                        @J.Hilk

                          while(t.elapsed() < 10000){
                        

                        Now, you doubtless know more than I about threads, because I don't use them. But I don't get this approach. It looks like you're spinning an awfully busy loop. It's true than your main thread will run uninterrupted, but half the CPU will be executing this all the time/your mobile battery is going to drain, no? Could you explain?

                        This is why the OP is asking about QEventLoop etc. Does a QThread run its own event loop? Does it exit when it gets to end of run() or does it have to be terminated explicitly?

                        jsulmJ Offline
                        jsulmJ Offline
                        jsulm
                        Lifetime Qt Champion
                        wrote on last edited by
                        #21

                        @JonB I think this is just a simple example not optimised for real world usage :-)

                        https://forum.qt.io/topic/113070/qt-code-of-conduct

                        1 Reply Last reply
                        1
                        • JonBJ JonB

                          @J.Hilk

                            while(t.elapsed() < 10000){
                          

                          Now, you doubtless know more than I about threads, because I don't use them. But I don't get this approach. It looks like you're spinning an awfully busy loop. It's true than your main thread will run uninterrupted, but half the CPU will be executing this all the time/your mobile battery is going to drain, no? Could you explain?

                          This is why the OP is asking about QEventLoop etc. Does a QThread run its own event loop? Does it exit when it gets to end of run() or does it have to be terminated explicitly?

                          J.HilkJ Offline
                          J.HilkJ Offline
                          J.Hilk
                          Moderators
                          wrote on last edited by
                          #22

                          @JonB I usually don't subclass QThread, but that's what the OP did so I went with the example.

                          It looks like you're spinning an awfully busy loop. It's true than your main thread will run uninterrupted, but half the CPU will be executing this all the time/your mobile battery is going to drain, no?

                          absolute correct. But this is really only a simulation of any busy calculation, that also shows, you don't need to to pause or spin the event loop to emit a signal that is handled in another thread.

                          Does a QThread run its own event loop? Does it exit when it gets to end of run() or does it have to be terminated explicitly?

                          the default QThread does indeed spin its own event loop. By overwriting run my subclass does this not by default.
                          everything inside run is executed in the new thread
                          If I want an event loop in SubThread, I would have to call exec()at the end of the run function. If not, the thread finishes as soon as the run function finishes.


                          Be aware of the Qt Code of Conduct, when posting : https://forum.qt.io/topic/113070/qt-code-of-conduct


                          Q: What's that?
                          A: It's blue light.
                          Q: What does it do?
                          A: It turns blue.

                          1 Reply Last reply
                          1
                          • JonBJ Offline
                            JonBJ Offline
                            JonB
                            wrote on last edited by
                            #23

                            @jsulm , @J-Hilk
                            Thank you for replies. I think I would really need to play with QThreads if it is to sink in! I thought this was code the OP was to type in & use, that's what happens here!

                            So just to be clear: if one really wanted to do what you have here --- emit a signal every so often --- one would set up a QTimer in the thread and then execute QThread::exec(), right?

                            J.HilkJ 1 Reply Last reply
                            0
                            • JonBJ JonB

                              @jsulm , @J-Hilk
                              Thank you for replies. I think I would really need to play with QThreads if it is to sink in! I thought this was code the OP was to type in & use, that's what happens here!

                              So just to be clear: if one really wanted to do what you have here --- emit a signal every so often --- one would set up a QTimer in the thread and then execute QThread::exec(), right?

                              J.HilkJ Offline
                              J.HilkJ Offline
                              J.Hilk
                              Moderators
                              wrote on last edited by
                              #24

                              @JonB If you want a regular Signal from the thread, triggered by a Timer then yes.

                              But the QTimer instance should be created inside run, or a function called from inside run. Otherwise the QTimer lives in the parent thread.


                              Be aware of the Qt Code of Conduct, when posting : https://forum.qt.io/topic/113070/qt-code-of-conduct


                              Q: What's that?
                              A: It's blue light.
                              Q: What does it do?
                              A: It turns blue.

                              1 Reply Last reply
                              0
                              • jsulmJ jsulm

                                @meganathan said in QProgressbar unresponsive with qthread:

                                all my remaining things that to done(after script execution) are already executed

                                Then do all these things in the slot connected to finished() signal as I already suggested.
                                "By using QEventloop can we block the until thread emits finished() signal.?" - you can, but then your progress bar will not update which was your first question in this thread, right? And if you anyway want to block, then why do you want to use threads? I don't see the point...

                                M Offline
                                M Offline
                                meganathan
                                wrote on last edited by
                                #25

                                @jsulm

                                QThread::finished signal() emits even before the thread completed it's process. The main reason for me to go for thread approach is because on using QProcess::waitforfinished(-1) makes my QProgress bar "Not responding" state.

                                Even i tried to emit the signal inside the Qthread::run() to update the GUI but on using thread->wait() makes GUI unresponsive yet again.

                                JonBJ J.HilkJ 2 Replies Last reply
                                0
                                • M meganathan

                                  @jsulm

                                  QThread::finished signal() emits even before the thread completed it's process. The main reason for me to go for thread approach is because on using QProcess::waitforfinished(-1) makes my QProgress bar "Not responding" state.

                                  Even i tried to emit the signal inside the Qthread::run() to update the GUI but on using thread->wait() makes GUI unresponsive yet again.

                                  JonBJ Offline
                                  JonBJ Offline
                                  JonB
                                  wrote on last edited by JonB
                                  #26

                                  @meganathan

                                  QThread::finished signal() emits even before the thread completed it's process.

                                  While you wait for @jsulm to reply, I imagine he'll want to ask you what you mean by the above? If you're not calling exec() it should emit when run() completes.

                                  1 Reply Last reply
                                  1
                                  • M meganathan

                                    @jsulm

                                    QThread::finished signal() emits even before the thread completed it's process. The main reason for me to go for thread approach is because on using QProcess::waitforfinished(-1) makes my QProgress bar "Not responding" state.

                                    Even i tried to emit the signal inside the Qthread::run() to update the GUI but on using thread->wait() makes GUI unresponsive yet again.

                                    J.HilkJ Offline
                                    J.HilkJ Offline
                                    J.Hilk
                                    Moderators
                                    wrote on last edited by
                                    #27

                                    @meganathan it would seriously help if you show us the content of your FelixThread class


                                    Be aware of the Qt Code of Conduct, when posting : https://forum.qt.io/topic/113070/qt-code-of-conduct


                                    Q: What's that?
                                    A: It's blue light.
                                    Q: What does it do?
                                    A: It turns blue.

                                    M 1 Reply Last reply
                                    4
                                    • J.HilkJ J.Hilk

                                      @meganathan it would seriously help if you show us the content of your FelixThread class

                                      M Offline
                                      M Offline
                                      meganathan
                                      wrote on last edited by
                                      #28

                                      @J.Hilk
                                      class FelixThread : public QThread
                                      {
                                      Q_OBJECT

                                      public:
                                      FelixThread(QDir tempDir,QString ansysPath,QMutex & mutexObj);
                                      public slots:
                                      void onExecutionFinished(int exitStatus);

                                      private:

                                      void run();    
                                      QProcess *process;
                                      

                                      signals:
                                      void progressChanged(int val);
                                      };

                                      1 Reply Last reply
                                      0

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