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When program quit, QSystemTrayIcon crashed.

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qsystemtrayiconcrashed
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  • ugiwghU ugiwgh

    @SGaist I want it new once, and call it in some other functions. It seems that it carsh, does not because of singletons. I new QTray, and show it, and then delete it, and then it crash.

    kshegunovK Offline
    kshegunovK Offline
    kshegunov
    Moderators
    wrote on last edited by
    #5

    @ugiwgh
    Your problem is you're calling destructors of QObject instances, after the root QObject (i.e. QApplication) has been destroyed. You just can't, shouldn't and mustn't do that. So yes, the singleton is responsible for that bloody mess, because variables with global storage are allocated before (but not necessarily constructed) and destroyed after main().

    One more remark:
    That trick with having a special object for cleanup is very tricky. You can lose the pointer to the object before invoking the delete operator, so you can be deleting a memory location pointed by an invalid variable that may (or may not) still hold a valid address; it would depend on the compiler implementation.
    I haven't actually checked the standard to see whether integral types are freed after objects with non-trivial destructors, but whatsoever it says, this way - to depend on the order of construction/destruction of static variables - is a terrible technique.

    Read and abide by the Qt Code of Conduct

    ugiwghU 2 Replies Last reply
    1
    • kshegunovK kshegunov

      @ugiwgh
      Your problem is you're calling destructors of QObject instances, after the root QObject (i.e. QApplication) has been destroyed. You just can't, shouldn't and mustn't do that. So yes, the singleton is responsible for that bloody mess, because variables with global storage are allocated before (but not necessarily constructed) and destroyed after main().

      One more remark:
      That trick with having a special object for cleanup is very tricky. You can lose the pointer to the object before invoking the delete operator, so you can be deleting a memory location pointed by an invalid variable that may (or may not) still hold a valid address; it would depend on the compiler implementation.
      I haven't actually checked the standard to see whether integral types are freed after objects with non-trivial destructors, but whatsoever it says, this way - to depend on the order of construction/destruction of static variables - is a terrible technique.

      ugiwghU Offline
      ugiwghU Offline
      ugiwgh
      wrote on last edited by
      #6

      @kshegunov I think you are right. Thanks for your help.

      1 Reply Last reply
      0
      • kshegunovK kshegunov

        @ugiwgh
        Your problem is you're calling destructors of QObject instances, after the root QObject (i.e. QApplication) has been destroyed. You just can't, shouldn't and mustn't do that. So yes, the singleton is responsible for that bloody mess, because variables with global storage are allocated before (but not necessarily constructed) and destroyed after main().

        One more remark:
        That trick with having a special object for cleanup is very tricky. You can lose the pointer to the object before invoking the delete operator, so you can be deleting a memory location pointed by an invalid variable that may (or may not) still hold a valid address; it would depend on the compiler implementation.
        I haven't actually checked the standard to see whether integral types are freed after objects with non-trivial destructors, but whatsoever it says, this way - to depend on the order of construction/destruction of static variables - is a terrible technique.

        ugiwghU Offline
        ugiwghU Offline
        ugiwgh
        wrote on last edited by
        #7

        @kshegunov

        It is nessary to add "instance_=NULL;" into destructor?

        class Tray : public QSystemTrayIcon
        {
        Q_OBJECT
        public:
        ~Tray() { instance_=NULL; }
        static Tray* instance()
        {
        if(NULL==instance_)
        {
        instance_=new PTray();
        }
        return instance_;
        }
        private:
        Tray(){}
        static Tray *instance_;
        };

        kshegunovK 1 Reply Last reply
        0
        • ugiwghU ugiwgh

          @kshegunov

          It is nessary to add "instance_=NULL;" into destructor?

          class Tray : public QSystemTrayIcon
          {
          Q_OBJECT
          public:
          ~Tray() { instance_=NULL; }
          static Tray* instance()
          {
          if(NULL==instance_)
          {
          instance_=new PTray();
          }
          return instance_;
          }
          private:
          Tray(){}
          static Tray *instance_;
          };

          kshegunovK Offline
          kshegunovK Offline
          kshegunov
          Moderators
          wrote on last edited by kshegunov
          #8

          @ugiwgh

          It is nessary to add "instance_=NULL;" into destructor?

          Well, no. This does nothing, as delete NULL is valid and does nothing. The object will be still in memory anyway. Beside refactoring your code and not using globally available objects (which the singleton is - basically a global variable) you can hook up the destruction to be tied to Qt's application object's life cycle. To do that you just parent the QObject you're creating to the QApplication object like this:

          class Tray : public QSystemTrayIcon
          {
              Q_OBJECT
          
          public:
              Tray(QObject *);
              ~Tray();
          
              static Tray * instance();
          };
          
          Tray::Tray(QObject * parent = NULL)
              : QSystemTrayIcon(parent)
          {
          }
          
          Tray::~Tray()
          {
              // Don't delete the object. Qt will delete it when the parent goes out of scope.
          }
          
          Tray * Tray::instance()
          {
              QCoreApplication * app = QCoreApplication::instance();
              Q_ASSERT(app); //< Make sure this is not called before the application was constructed.
              
              static Tray * trayInstance = new Tray(app);
              return trayInstance;
          }
          

          Again, it's better to not have singletons at all, C++ is not Java and not everything that's written in books about Java (or is common there) is applicable to C++. But the above snippet should work, although I haven't tested it.

          Read and abide by the Qt Code of Conduct

          ugiwghU 1 Reply Last reply
          0
          • kshegunovK kshegunov

            @ugiwgh

            It is nessary to add "instance_=NULL;" into destructor?

            Well, no. This does nothing, as delete NULL is valid and does nothing. The object will be still in memory anyway. Beside refactoring your code and not using globally available objects (which the singleton is - basically a global variable) you can hook up the destruction to be tied to Qt's application object's life cycle. To do that you just parent the QObject you're creating to the QApplication object like this:

            class Tray : public QSystemTrayIcon
            {
                Q_OBJECT
            
            public:
                Tray(QObject *);
                ~Tray();
            
                static Tray * instance();
            };
            
            Tray::Tray(QObject * parent = NULL)
                : QSystemTrayIcon(parent)
            {
            }
            
            Tray::~Tray()
            {
                // Don't delete the object. Qt will delete it when the parent goes out of scope.
            }
            
            Tray * Tray::instance()
            {
                QCoreApplication * app = QCoreApplication::instance();
                Q_ASSERT(app); //< Make sure this is not called before the application was constructed.
                
                static Tray * trayInstance = new Tray(app);
                return trayInstance;
            }
            

            Again, it's better to not have singletons at all, C++ is not Java and not everything that's written in books about Java (or is common there) is applicable to C++. But the above snippet should work, although I haven't tested it.

            ugiwghU Offline
            ugiwghU Offline
            ugiwgh
            wrote on last edited by
            #9

            @kshegunov
            I have tested that. It crashed.
            If I add tray->hide() after app.exec(). It normal exit.

            (gdb) bt
            #0 0x000000000045821a in QWidget::~QWidget() ()
            #1 0x00000000008b79a9 in QBalloonTip::~QBalloonTip() ()
            #2 0x00000000008b6cca in QBalloonTip::hideBalloon() ()
            #3 0x00000000008c6e33 in QSystemTrayIconPrivate::remove_sys() ()
            #4 0x00000000008b7bef in QSystemTrayIcon::~QSystemTrayIcon() ()
            #5 0x00000000004124b9 in Tray::~Tray (this=0x2878cc0, __in_chrg=<value optimized out>)
            at tray.cpp:26
            #6 0x00000000004124f0 in Tray::~Tray (this=0x2878cc0, __in_chrg=<value optimized out>)
            at tray.cpp:26
            #7 0x0000000000ba1f67 in QObjectPrivate::deleteChildren() ()
            #8 0x0000000000ba84b6 in QObject::~QObject() ()
            #9 0x000000000042568c in QApplication::~QApplication() ()
            #10 0x00000000004121af in QtSingleApplication::~QtSingleApplication (this=0x7fff44a4b6f0,
            __in_chrg=<value optimized out>) at ../qtsingleapplication/src/qtsingleapplication.h:65
            #11 0x0000000000411c8f in main (argc=1, argv=0x7fff44a4b898) at main.cpp:103

            kshegunovK 1 Reply Last reply
            0
            • ugiwghU ugiwgh

              @kshegunov
              I have tested that. It crashed.
              If I add tray->hide() after app.exec(). It normal exit.

              (gdb) bt
              #0 0x000000000045821a in QWidget::~QWidget() ()
              #1 0x00000000008b79a9 in QBalloonTip::~QBalloonTip() ()
              #2 0x00000000008b6cca in QBalloonTip::hideBalloon() ()
              #3 0x00000000008c6e33 in QSystemTrayIconPrivate::remove_sys() ()
              #4 0x00000000008b7bef in QSystemTrayIcon::~QSystemTrayIcon() ()
              #5 0x00000000004124b9 in Tray::~Tray (this=0x2878cc0, __in_chrg=<value optimized out>)
              at tray.cpp:26
              #6 0x00000000004124f0 in Tray::~Tray (this=0x2878cc0, __in_chrg=<value optimized out>)
              at tray.cpp:26
              #7 0x0000000000ba1f67 in QObjectPrivate::deleteChildren() ()
              #8 0x0000000000ba84b6 in QObject::~QObject() ()
              #9 0x000000000042568c in QApplication::~QApplication() ()
              #10 0x00000000004121af in QtSingleApplication::~QtSingleApplication (this=0x7fff44a4b6f0,
              __in_chrg=<value optimized out>) at ../qtsingleapplication/src/qtsingleapplication.h:65
              #11 0x0000000000411c8f in main (argc=1, argv=0x7fff44a4b898) at main.cpp:103

              kshegunovK Offline
              kshegunovK Offline
              kshegunov
              Moderators
              wrote on last edited by
              #10

              @ugiwgh
              Can you provide a minimal project that reproduces the crash (e.g. in a git repository somewhere)?

              That's strange, but what's stranger is this:

              #10 0x00000000004121af in QtSingleApplication::~QtSingleApplication (this=0x7fff44a4b6f0,
              __in_chrg=<value optimized out>) at ../qtsingleapplication/src/qtsingleapplication.h:65
              

              What is this and how it got there?

              Read and abide by the Qt Code of Conduct

              ugiwghU 1 Reply Last reply
              0
              • kshegunovK kshegunov

                @ugiwgh
                Can you provide a minimal project that reproduces the crash (e.g. in a git repository somewhere)?

                That's strange, but what's stranger is this:

                #10 0x00000000004121af in QtSingleApplication::~QtSingleApplication (this=0x7fff44a4b6f0,
                __in_chrg=<value optimized out>) at ../qtsingleapplication/src/qtsingleapplication.h:65
                

                What is this and how it got there?

                ugiwghU Offline
                ugiwghU Offline
                ugiwgh
                wrote on last edited by
                #11

                @kshegunov
                I have upload it there.
                https://github.com/ugiwgh/qsystemtray/
                https://github.com/ugiwgh/qsystemtray.git

                kshegunovK 1 Reply Last reply
                0
                • ugiwghU ugiwgh

                  @kshegunov
                  I have upload it there.
                  https://github.com/ugiwgh/qsystemtray/
                  https://github.com/ugiwgh/qsystemtray.git

                  kshegunovK Offline
                  kshegunovK Offline
                  kshegunov
                  Moderators
                  wrote on last edited by
                  #12

                  @ugiwgh
                  Well works okay on my machine - no crashes. I even see an empty space in the tray where when I click I get a context menu and I can choose to quit. When I do, everything works as expected and the program exits.

                  However, you shouldn't use QtSingleApplication as it seems to be ancient, you'd be better off looking for newer alternatives.

                  Read and abide by the Qt Code of Conduct

                  ugiwghU 1 Reply Last reply
                  0
                  • kshegunovK kshegunov

                    @ugiwgh
                    Well works okay on my machine - no crashes. I even see an empty space in the tray where when I click I get a context menu and I can choose to quit. When I do, everything works as expected and the program exits.

                    However, you shouldn't use QtSingleApplication as it seems to be ancient, you'd be better off looking for newer alternatives.

                    ugiwghU Offline
                    ugiwghU Offline
                    ugiwgh
                    wrote on last edited by
                    #13

                    @kshegunov
                    Yes. I have disabled QtSingleApplication. And I have update the code on github.
                    It also crashed, when I choose to quit.

                    #0 0x00007f094a93564a in QWidget::~QWidget() ()
                    from /opt/qt-5.4.1/5.4/gcc_64/lib/libQt5Widgets.so.5
                    #1 0x00007f094ac92f0e in ?? () from /opt/qt-5.4.1/5.4/gcc_64/lib/libQt5Widgets.so.5
                    #2 0x00007f094ac92b25 in ?? () from /opt/qt-5.4.1/5.4/gcc_64/lib/libQt5Widgets.so.5
                    #3 0x00007f094ac735eb in QSystemTrayIcon::~QSystemTrayIcon() ()
                    from /opt/qt-5.4.1/5.4/gcc_64/lib/libQt5Widgets.so.5
                    #4 0x0000000000403625 in PTray::~PTray (this=0x22a1e60,
                    __in_chrg=<value optimized out>) at para_tray.cpp:26
                    #5 0x000000000040365c in PTray::~PTray (this=0x22a1e60,
                    __in_chrg=<value optimized out>) at para_tray.cpp:26
                    #6 0x00007f0949ba4b1a in QObjectPrivate::deleteChildren() ()
                    from /opt/qt-5.4.1/5.4/gcc_64/lib/libQt5Core.so.5
                    #7 0x00007f0949baa259 in QObject::~QObject() ()
                    from /opt/qt-5.4.1/5.4/gcc_64/lib/libQt5Core.so.5
                    #8 0x00007f094a8edda8 in QApplication::~QApplication() ()
                    from /opt/qt-5.4.1/5.4/gcc_64/lib/libQt5Widgets.so.5
                    #9 0x0000000000403129 in main (argc=1, argv=0x7ffff084acf8) at main.cpp:23

                    kshegunovK 1 Reply Last reply
                    0
                    • ugiwghU ugiwgh

                      @kshegunov
                      Yes. I have disabled QtSingleApplication. And I have update the code on github.
                      It also crashed, when I choose to quit.

                      #0 0x00007f094a93564a in QWidget::~QWidget() ()
                      from /opt/qt-5.4.1/5.4/gcc_64/lib/libQt5Widgets.so.5
                      #1 0x00007f094ac92f0e in ?? () from /opt/qt-5.4.1/5.4/gcc_64/lib/libQt5Widgets.so.5
                      #2 0x00007f094ac92b25 in ?? () from /opt/qt-5.4.1/5.4/gcc_64/lib/libQt5Widgets.so.5
                      #3 0x00007f094ac735eb in QSystemTrayIcon::~QSystemTrayIcon() ()
                      from /opt/qt-5.4.1/5.4/gcc_64/lib/libQt5Widgets.so.5
                      #4 0x0000000000403625 in PTray::~PTray (this=0x22a1e60,
                      __in_chrg=<value optimized out>) at para_tray.cpp:26
                      #5 0x000000000040365c in PTray::~PTray (this=0x22a1e60,
                      __in_chrg=<value optimized out>) at para_tray.cpp:26
                      #6 0x00007f0949ba4b1a in QObjectPrivate::deleteChildren() ()
                      from /opt/qt-5.4.1/5.4/gcc_64/lib/libQt5Core.so.5
                      #7 0x00007f0949baa259 in QObject::~QObject() ()
                      from /opt/qt-5.4.1/5.4/gcc_64/lib/libQt5Core.so.5
                      #8 0x00007f094a8edda8 in QApplication::~QApplication() ()
                      from /opt/qt-5.4.1/5.4/gcc_64/lib/libQt5Widgets.so.5
                      #9 0x0000000000403129 in main (argc=1, argv=0x7ffff084acf8) at main.cpp:23

                      kshegunovK Offline
                      kshegunovK Offline
                      kshegunov
                      Moderators
                      wrote on last edited by kshegunov
                      #14

                      @ugiwgh
                      Well, I don't know man. As I said, I had run your code (the link you provided in your previous post) and it worked okay on my machine, no crashes whatsoever.
                      If it helps I'm running Debian stretch (4.4.0 kernel) + KDE plasma desktop and I used Qt 5.5.1 for the test run. You may have stumbled on a bug or possibly some platform dependent code is not executing properly, I can't tell really.

                      EDIT:
                      I only just now saw something:

                      #4 0x0000000000403625 in PTray::~PTray (this=0x22a1e60,
                      __in_chrg=<value optimized out>) at para_tray.cpp:26
                      #5 0x000000000040365c in PTray::~PTray (this=0x22a1e60,
                      __in_chrg=<value optimized out>) at para_tray.cpp:26
                      

                      Why do you have 2 calls to your destructor??!

                      Read and abide by the Qt Code of Conduct

                      1 Reply Last reply
                      0
                      • SGaistS Offline
                        SGaistS Offline
                        SGaist
                        Lifetime Qt Champion
                        wrote on last edited by
                        #15

                        Like @kshegunov already wrote using singleton should be avoided when possible and your use case really does't need any singleton.

                        It sounds that you are rather creating tight coupling between your different classes rather that have a lean path to use system tray.

                        So what are all these classes doing with the system tray icon and that menu ?

                        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
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