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qt application crash.

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  • A Offline
    A Offline
    Anas_Deshmukh
    wrote on last edited by Anas_Deshmukh
    #1

    hi everyone,
    i am getting below error, dont know how to figure out what exactly goin wrong.

    [xcb] Unknown sequence number while processing queue
    [xcb] Most likely this is a multi-threaded client and XInitThreads has not been called
    [xcb] Aborting, sorry about that.
    sps_v1: ../../src/xcb_io.c:274: poll_for_event: Assertion `!xcb_xlib_threads_sequence_lost' failed.
    The program has unexpectedly finished.

    thanx in advance.

    P.S. edit : also getting
    QPixmap: It is not safe to use pixmaps outside the GUI thread

    kshegunovK 1 Reply Last reply
    0
    • mrjjM Offline
      mrjjM Offline
      mrjj
      Lifetime Qt Champion
      wrote on last edited by
      #2

      Hi
      you should provide more details about OS version/platform
      and Qt version,
      when error happens.

      Also try it on other computer.

      1 Reply Last reply
      1
      • A Anas_Deshmukh

        hi everyone,
        i am getting below error, dont know how to figure out what exactly goin wrong.

        [xcb] Unknown sequence number while processing queue
        [xcb] Most likely this is a multi-threaded client and XInitThreads has not been called
        [xcb] Aborting, sorry about that.
        sps_v1: ../../src/xcb_io.c:274: poll_for_event: Assertion `!xcb_xlib_threads_sequence_lost' failed.
        The program has unexpectedly finished.

        thanx in advance.

        P.S. edit : also getting
        QPixmap: It is not safe to use pixmaps outside the GUI thread

        kshegunovK Offline
        kshegunovK Offline
        kshegunov
        Moderators
        wrote on last edited by
        #3

        I suspect you're using the GUI classes from different threads. Please provide code to confirm or deny this.

        Read and abide by the Qt Code of Conduct

        1 Reply Last reply
        0
        • A Offline
          A Offline
          Anas_Deshmukh
          wrote on last edited by
          #4

          @mrjj @kshegunov Thanks for reply.

          result of command : lsb_release -a
          No LSB modules are available.
          Distributor ID: Ubuntu
          Description: Ubuntu 14.04.2 LTS
          Release: 14.04
          Codename: trusty

          Qt version : 4.8.6

          @kshegunov : i cant provide code, its big application.

          I am having scanner class which continuously running in thread and detecting scanner available or not and emit the signal when scanning event happen. further i used this signal to various slot as per need.

          I create one more class to monitor all USB devices including scanner which are connected.
          error occurred when specifically scanner not connected.

          I am very thankful if you suggest me correct approach to monitor all usb connection status. so that any thread wont get affected.

          1 Reply Last reply
          0
          • A Offline
            A Offline
            Anas_Deshmukh
            wrote on last edited by
            #5

            meanwhile tried with flag Qt::AA_X11InitThreads. but nothing works
            for now i add below lines in .pro file

            QMAKE_CXXFLAGS += -std=c++0x -pthread
            LIBS += -pthread
            

            and add libraires in main.cpp and simply called XInitThreads();
            but after calling function XInitThreads().
            my application crash when i tried to call qmessagebox from some function.

            
            #include <thread>
            #include <X11/Xlib.h>
            
            Q_DECL_EXPORT int main(int argc, char *argv[])
            {
                QScopedPointer<QApplication> app(createApplication(argc, argv));
            
                XInitThreads();  // if coment  -  `!xcb_xlib_threads_sequence_lost' failed. appeared.
            
            
            //    app->setAttribute(Qt::AA_X11InitThreads, true);  // setting flag has no effect so far
            
                QmlApplicationViewer viewer;
            ...
            ...
            
            }
            
            // test.cpp
            
            someFunction() {
            ...
                QMessageBox *msgBox = new QMessageBox();
                int retValue=msgBox->exec(); // crash here.
            ...
            }
            
            1 Reply Last reply
            0
            • A Offline
              A Offline
              Anas_Deshmukh
              wrote on last edited by
              #6

              Hi everyone,

              I read about Qt::AA_X11InitThreads and it clearly mention as "Calls XInitThreads() as part of the QApplication construction in order to make Xlib calls thread-safe. This attribute must be set before QApplication is constructed."

              now I removed these flags from .pro file

              QMAKE_CXXFLAGS += -std=c++0x -pthread
              LIBS += -pthread
              

              and updated main.cpp file

              
              Q_DECL_EXPORT int main(int argc, char *argv[])
              {
                  QApplication::setAttribute(Qt::AA_X11InitThreads);
              
                  QScopedPointer<QApplication> app(createApplication(argc, argv));
              
              //    XInitThreads();
              //    app->setAttribute(Qt::AA_X11InitThreads, true);
              
                  QmlApplicationViewer viewer;
              
              ...
              }
              

              Problem is fixed so far. thanks.

              1 Reply Last reply
              1

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