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Image Scaling Example freezes (qt concurrent issue)

  • I built and run the official Image Scaling Example, it freezes if 12 or more files were selected.

    My env:

    the debug call stack show

  • Found some clues.

    My CPU is AMD Ryzen 5 1600, 6 cores, 12 logical cores.

    When AMD SMT is enabled, there are 12 logical cores available, and QFutureWatcher::setFuture() will freeze if 12 or more concurrent tasks are queued.
    When SMT feature is disabled, setFuture() will freeze when 6 tasks or more are queued.

    The qt freezes when 12 (or 6 w/o SMT) tasks complete.

    OS: Windows 10 Pro, 1903, 18362.1016

  • Is it possible to use qtconcurrent function without OpenGL involved? It seems that qt blocks in OpenGL relative calls.


  • This bug has been resolved in Qt 5.15.1.

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