Skip to content
  • Categories
  • Recent
  • Tags
  • Popular
  • Users
  • Groups
  • Search
  • Get Qt Extensions
  • Unsolved
Collapse
Brand Logo
  1. Home
  2. Qt Development
  3. General and Desktop
  4. How to know thread is running from different button ?
Forum Updated to NodeBB v4.3 + New Features

How to know thread is running from different button ?

Scheduled Pinned Locked Moved Solved General and Desktop
22 Posts 5 Posters 6.8k Views 1 Watching
  • Oldest to Newest
  • Newest to Oldest
  • Most Votes
Reply
  • Reply as topic
Log in to reply
This topic has been deleted. Only users with topic management privileges can see it.
  • A a normal worker

    @Hiloshi Maybe my idea is not clear. Your code is created with two different objects, so their states are different. You should make sure that you use a class member variable or they point to the same object

    jsulmJ Offline
    jsulmJ Offline
    jsulm
    Lifetime Qt Champion
    wrote on last edited by
    #7

    @a-normal-worker "You should make sure that you use a class member variable or they point to the same object" - he already does in his last post.

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

    1 Reply Last reply
    1
    • H Offline
      H Offline
      Hiloshi
      wrote on last edited by
      #8

      Dear @jsulm , @a-normal-worker ,

      Thank you all. First, the "redefine of class xxxxx" issue may cause by a silly mistake:

      #ifndef MYTHREAD_H
      #define MYTHREAD_H
      #endif 
      class MyThread   // <--I put my code here.
      

      After fix above mistake and declare T3Thread pointer correctly then can compiler successfully.

      But running the program show a strange message: "Process killed by signal"

      In MyThread.h:

      class MyThread : public QThread
      {
          Q_OBJECT
      
      private:
          void run()
           {       
              for (int i = 0; i <= 100; i++)
              {            
                  delay(20);
              }       
           }
      };
      

      In mainwindow.h:

      class MyThread;
      
      class MainWindow : public QMainWindow
      {
          Q_OBJECT
      
      public:
          explicit MainWindow(QWidget *parent = 0);
          ~MainWindow();
      
      private slots:
          void on_pushButton_pressed();
      
          void on_pushButton_2_clicked();
      
      private:
          Ui::MainWindow *ui;
          MyThread *T3Thread;
      };
      

      In mainwindow.cpp:

      #include "mythread.h"
      
      MainWindow::MainWindow(QWidget *parent) :
          QMainWindow(parent),
          ui(new Ui::MainWindow)
      {
          ui->setupUi(this);   
          MyThread  *T3Thread = new MyThread;
          T3Thread->start();
      }
      void MainWindow::on_pushButton_12_clicked()
      {
          T3Thread->start();
      }
      

      When I run the program, the screen show as normal, but when I press button_2, the screen close suddently, and show "Process killed by signal" on QT terminal.

      I suspect that problem is cause by T3Thread->start(), however, if I didn't press button_2, nothing happened.
      T3Thread should also executed while creating main window?

      Do I lack some declaration ?

      jsulmJ 1 Reply Last reply
      0
      • SGaistS Offline
        SGaistS Offline
        SGaist
        Lifetime Qt Champion
        wrote on last edited by
        #9

        Your constructor is wrong. You are shadowing your T3Thread member variable. Thus when you call on_pushButton_12_clicked you are trying to access an uninitialised pointer hence the crash.

        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
        • H Hiloshi

          Dear @jsulm , @a-normal-worker ,

          Thank you all. First, the "redefine of class xxxxx" issue may cause by a silly mistake:

          #ifndef MYTHREAD_H
          #define MYTHREAD_H
          #endif 
          class MyThread   // <--I put my code here.
          

          After fix above mistake and declare T3Thread pointer correctly then can compiler successfully.

          But running the program show a strange message: "Process killed by signal"

          In MyThread.h:

          class MyThread : public QThread
          {
              Q_OBJECT
          
          private:
              void run()
               {       
                  for (int i = 0; i <= 100; i++)
                  {            
                      delay(20);
                  }       
               }
          };
          

          In mainwindow.h:

          class MyThread;
          
          class MainWindow : public QMainWindow
          {
              Q_OBJECT
          
          public:
              explicit MainWindow(QWidget *parent = 0);
              ~MainWindow();
          
          private slots:
              void on_pushButton_pressed();
          
              void on_pushButton_2_clicked();
          
          private:
              Ui::MainWindow *ui;
              MyThread *T3Thread;
          };
          

          In mainwindow.cpp:

          #include "mythread.h"
          
          MainWindow::MainWindow(QWidget *parent) :
              QMainWindow(parent),
              ui(new Ui::MainWindow)
          {
              ui->setupUi(this);   
              MyThread  *T3Thread = new MyThread;
              T3Thread->start();
          }
          void MainWindow::on_pushButton_12_clicked()
          {
              T3Thread->start();
          }
          

          When I run the program, the screen show as normal, but when I press button_2, the screen close suddently, and show "Process killed by signal" on QT terminal.

          I suspect that problem is cause by T3Thread->start(), however, if I didn't press button_2, nothing happened.
          T3Thread should also executed while creating main window?

          Do I lack some declaration ?

          jsulmJ Offline
          jsulmJ Offline
          jsulm
          Lifetime Qt Champion
          wrote on last edited by
          #10

          @Hiloshi To add to @SGaist : why do you start the thread twice (once in the constructor and then in on_pushButton_12_clicked())?

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

          1 Reply Last reply
          1
          • H Offline
            H Offline
            Hiloshi
            wrote on last edited by Hiloshi
            #11

            Dear @jsulm , @SGaist

            Sorry to confuse you, I didn't explain clearly.

            If I use "new" and "T3Thread->start" in the same area, then it will no error(process killed by signal),
            as below:
            https://www.dropbox.com/s/0488sqlhgn9u4wf/Screenshot from 2017-04-06 09-28-32.png?dl=0
            alt text

            However, if I put them in different place, application will crash and return "process killed by signal",
            as below:
            https://www.dropbox.com/s/3dfists06z3c5q9/Screenshot from 2017-04-06 09-33-10.png?dl=0
            alt text

            Moreover, if I put "new" just after the "ui->setupUi(this)" and "T3Thread in the on_pushButton_clicked,
            it will show a warning message "unused variable ‘T3Thread’ [-Wunused-variable]".

            @SGaist , I think maybe this is what you said : "uninitialised pointer " .

            But, I am sorry, I don't know how to correct it.

            jsulmJ 1 Reply Last reply
            0
            • SGaistS Offline
              SGaistS Offline
              SGaist
              Lifetime Qt Champion
              wrote on last edited by
              #12

              Remove MyThread * from your constructor.

              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
              • H Hiloshi

                Dear @jsulm , @SGaist

                Sorry to confuse you, I didn't explain clearly.

                If I use "new" and "T3Thread->start" in the same area, then it will no error(process killed by signal),
                as below:
                https://www.dropbox.com/s/0488sqlhgn9u4wf/Screenshot from 2017-04-06 09-28-32.png?dl=0
                alt text

                However, if I put them in different place, application will crash and return "process killed by signal",
                as below:
                https://www.dropbox.com/s/3dfists06z3c5q9/Screenshot from 2017-04-06 09-33-10.png?dl=0
                alt text

                Moreover, if I put "new" just after the "ui->setupUi(this)" and "T3Thread in the on_pushButton_clicked,
                it will show a warning message "unused variable ‘T3Thread’ [-Wunused-variable]".

                @SGaist , I think maybe this is what you said : "uninitialised pointer " .

                But, I am sorry, I don't know how to correct it.

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

                @Hiloshi You should really read more carefully what others are writing. What @SGaist said is:

                MainWindow::MainWindow(QWidget *parent) :
                    QMainWindow(parent),
                    ui(new Ui::MainWindow)
                {
                    ui->setupUi(this);   
                    T3Thread = new MyThread; // Remove MyThread* - else you are declaring a local variable which is completely unrelated to the one in your header!
                    T3Thread->start();
                }
                

                And after this change think about where to start the thread: in the code you posted you're doing it twice.

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

                1 Reply Last reply
                1
                • H Offline
                  H Offline
                  Hiloshi
                  wrote on last edited by
                  #14

                  Very happy to learn from here. Thanks everyone.

                  1 Reply Last reply
                  0
                  • H Offline
                    H Offline
                    Hiloshi
                    wrote on last edited by
                    #15

                    I want to study in depth in this question. In the original question, I have a running T3Thread, mainwindow cannot reach T3Thread, thanks for @a-normal-worker 's suggestion, we can make T3Thread as a class member of mainwindow then mainwindow have ability to access T3Thread.

                    Can we use signal/slot instead of using class member ?

                    1 Reply Last reply
                    0
                    • SGaistS Offline
                      SGaistS Offline
                      SGaist
                      Lifetime Qt Champion
                      wrote on last edited by
                      #16

                      What exactly do you want to do with your thread ?

                      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
                      • H Offline
                        H Offline
                        Hiloshi
                        wrote on last edited by
                        #17

                        Dear @SGaist ,

                        I am thinking to create a breathing LED in my thread, "run" function is keep turn on/off LED.
                        I want to put one button on mainwindow to start the thread.

                        I do not want this button to be pressed twice ( or thread will create twice), so in the button I put:

                        void MainWindow::on_pushButton_3_clicked()
                        {
                            if(T3Thread->isRunning()==false)
                            {
                                MyThread  *T3Thread = new MyThread;  // local variable
                                T3Thread->start;
                            }
                            else
                                qDebug()<<"T3 thread is running";
                        }
                        

                        If I do not want to use class member, can I use signal/slot to know T3Thread is running or not ?

                        Thanks.

                        J.HilkJ 1 Reply Last reply
                        0
                        • H Hiloshi

                          Dear @SGaist ,

                          I am thinking to create a breathing LED in my thread, "run" function is keep turn on/off LED.
                          I want to put one button on mainwindow to start the thread.

                          I do not want this button to be pressed twice ( or thread will create twice), so in the button I put:

                          void MainWindow::on_pushButton_3_clicked()
                          {
                              if(T3Thread->isRunning()==false)
                              {
                                  MyThread  *T3Thread = new MyThread;  // local variable
                                  T3Thread->start;
                              }
                              else
                                  qDebug()<<"T3 thread is running";
                          }
                          

                          If I do not want to use class member, can I use signal/slot to know T3Thread is running or not ?

                          Thanks.

                          J.HilkJ Offline
                          J.HilkJ Offline
                          J.Hilk
                          Moderators
                          wrote on last edited by J.Hilk
                          #18

                          @Hiloshi
                          ok, I think we talk at cross here.

                          Here's a basic setup to check if your thread is running when you press a Button, if its not running the button will start the thread:

                          //in your header:
                          example.h
                          
                          #include <QThread>
                          #include <qDebug>
                          
                          private:
                          QThread *thread;
                          
                          //in your source file
                          
                          //Constructor
                          {
                              ui->setupUi(this);   
                              thread = new QThread;
                          ....
                          }
                          
                          
                          void on_pushButton_clicked(){
                             if(thread->isRunning())
                                qDebug() << "Thread is running";
                             else{
                                qDebug() << "Thread started";
                                thread->start(); 
                             }
                          }
                          
                          //Destructor
                          {
                            if(thread->isRunning()){
                             thread->quit();
                             thread-> wait();
                            }
                          ...
                            delete ui;
                          }
                          

                          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
                          • SGaistS Offline
                            SGaistS Offline
                            SGaist
                            Lifetime Qt Champion
                            wrote on last edited by
                            #19

                            What is the problem with using a member variable to handle that thread object properly ?

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

                            H 1 Reply Last reply
                            1
                            • SGaistS SGaist

                              What is the problem with using a member variable to handle that thread object properly ?

                              H Offline
                              H Offline
                              Hiloshi
                              wrote on last edited by
                              #20

                              @SGaist , There is no problem using member variable. I just thinking if it possible to use signal/slot to reach the same purpose.

                              1 Reply Last reply
                              0
                              • SGaistS Offline
                                SGaistS Offline
                                SGaist
                                Lifetime Qt Champion
                                wrote on last edited by
                                #21

                                There could be ways however you are talking about creating an object somewhere without any reference to it and still want to interact with it. That's bad by design.

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

                                H 1 Reply Last reply
                                1
                                • SGaistS SGaist

                                  There could be ways however you are talking about creating an object somewhere without any reference to it and still want to interact with it. That's bad by design.

                                  H Offline
                                  H Offline
                                  Hiloshi
                                  wrote on last edited by Hiloshi
                                  #22

                                  @SGaist , Understood, thanks for the help.

                                  1 Reply Last reply
                                  0

                                  • Login

                                  • Login or register to search.
                                  • First post
                                    Last post
                                  0
                                  • Categories
                                  • Recent
                                  • Tags
                                  • Popular
                                  • Users
                                  • Groups
                                  • Search
                                  • Get Qt Extensions
                                  • Unsolved