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Thread: Signal isn't catched in Thread

  1. #1
    Join Date
    Feb 2016
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    Qt products
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    Platforms
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    Default Signal isn't catched in Thread

    I want to fire a signal to an Object that moved into a QThread, it doesn't receive fired "startFlash" signal. Below is my code:

    Qt Code:
    1. //mainwindow.cpp
    2. .....
    3. ThreadFlasher = new QThread;
    4. flasher = new Flasher(0);
    5. .....
    6. connect(ThreadFlasher, SIGNAL(started()), flasher, SLOT(process())); // This works, process function in flasher runs
    7. connect(this, SIGNAL(stopThread()), flasher, SLOT(stopThread()));
    8. connect(this, SIGNAL(startFlash()), flasher, SLOT(startFlash()));
    9. ...
    10.  
    11. void MainWindow::on_pushButtonFW_clicked()
    12. {
    13. emit startFlash();
    14. }
    15. void MainWindow::on_openButtonConnect_clicked()
    16. {
    17. flasher->moveToThread(ThreadFlasher);
    18. ThreadFlasher->start();
    19. }
    20.  
    21.  
    22. ....
    23. //Flasher.cpp
    24.  
    25. void Flasher::process()
    26. {
    27. while(run)
    28. {
    29. msleep(10); // I think There is not enough time to get variable startFlashing?
    30. if(startFlashing)
    31. {
    32. FLASH_StartFlash();
    33. startFlashing = false;
    34. }
    35. }
    36. emit finished();
    37. }
    38.  
    39. void Flasher::startFlash()
    40. {
    41. startFlashing = true;
    42. }
    43. void Flasher::stopThread()
    44. {
    45. run = false;
    46. }
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  2. #2
    Join Date
    Sep 2011
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    Qt products
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    Default Re: Signal isn't catched in Thread

    Ok then, I tell You how I solved this problem. I will explain to You what seems to be going on in Your code.
    When You start process() function which is a slot You block event loop in QThread because of while loop. I did the same.
    The solution is to use code whith QEventLoop and QTimer. Here is a loop You can try.

    Qt Code:
    1. void
    2. QTimer timer;
    3. timer.setSingleShot(true);
    4. QObject::connect(&timer, SIGNAL(timeout), &loop, SLOT(quit());
    5.  
    6. startLoop:
    7. {
    8. timer.start(20);
    9. loop.exec()
    10.  
    11.  
    12. // (...)
    13.  
    14.  
    15.  
    16. }
    17. if(run)
    18. {
    19. gotoLoop:
    20. }
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  3. #3
    Join Date
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    Qt products
    Qt3 Qt4 Qt5
    Platforms
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    Default Re: Signal isn't catched in Thread

    The solution is to not block the thread's event loop.

    This looks like there is no need for process() at all, this could just call FLASH_StartFlash() in startFlash()

    Cheers,
    _

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