Details
-
Bug
-
Resolution: Incomplete
-
P2: Important
-
None
-
6.4.2
-
None
-
Windows 10
-
Windows
Description
My app was running in background (i.e. main window was hidden). When I switched to it, I've found that it does not respond. I made dump of it and found that the main thread is stuck with the following stack trace:
ntdll.dll!NtWaitForSingleObject() KERNELBASE.dll!WaitForSingleObjectEx() [Inline Frame] Qt6Core.dll!QWaitConditionPrivate::wait(QWaitConditionEvent *) Line 75 Qt6Core.dll!QWaitCondition::wait(QMutex * mutex, unsigned long time) Line 133 Qt6Core.dll!QWaitCondition::wait(QMutex * mutex, QDeadlineTimer deadline) Line 144 Qt6Quick.dll!QSGThreadedRenderLoop::polishAndSync(QSGThreadedRenderLoop::Window * w, bool inExpose) Line 1586 Qt6Quick.dll!QSGThreadedRenderLoop::handleExposure(QQuickWindow * window) Line 1289 Qt6Gui.dll!QWindow::event(QEvent * ev) Line 2473 Qt6Widgets.dll!QApplicationPrivate::notify_helper(QObject * receiver, QEvent * e) Line 3317 Qt6Widgets.dll!QApplication::notify(QObject * receiver, QEvent * e) Line 3269 Qt6Core.dll!QCoreApplication::notifyInternal2(QObject * receiver, QEvent * event) Line 1026 Qt6Gui.dll!QGuiApplicationPrivate::processExposeEvent(QWindowSystemInterfacePrivate::ExposeEvent * e) Line 3188 Qt6Gui.dll!QWindowSystemInterface::sendWindowSystemEvents(QFlags<enum QEventLoop::ProcessEventsFlag> flags) Line 1109 Qt6Gui.dll!QWindowSystemInterface::flushWindowSystemEvents(QFlags<enum QEventLoop::ProcessEventsFlag> flags) Line 1074 qwindows.dll!00007ff8a1adc800() qwindows.dll!00007ff8a1a8b453() qwindows.dll!00007ff8a1a8c1d3() user32.dll!UserCallWinProcCheckWow() user32.dll!DispatchClientMessage() user32.dll!__fnDWORD() ntdll.dll!KiUserCallbackDispatcherContinue() win32u.dll!NtUserDispatchMessage() user32.dll!DispatchMessageWorker() Qt6Core.dll!QEventDispatcherWin32::processEvents(QFlags<enum QEventLoop::ProcessEventsFlag> flags) Line 533 Qt6Gui.dll!QWindowsGuiEventDispatcher::processEvents(QFlags<enum QEventLoop::ProcessEventsFlag> flags) Line 37 [Inline Frame] Qt6Core.dll!QEventLoop::processEvents(QFlags<enum QEventLoop::ProcessEventsFlag>) Line 100 Qt6Core.dll!QEventLoop::exec(QFlags<enum QEventLoop::ProcessEventsFlag> flags) Line 182 Qt6Core.dll!QCoreApplication::exec() Line 1347
This is similar to QTBUG-86329 except that it seems there is no interference from a third party software.
It seems the culprit of the deadlock is another thread stuck with the following stack trace:
ntdll.dll!NtWaitForSingleObject()
KERNELBASE.dll!WaitForSingleObjectEx()
[Inline Frame] Qt6Core.dll!QWaitConditionPrivate::wait(QWaitConditionEvent *) Line 75
Qt6Core.dll!QWaitCondition::wait(QMutex * mutex, unsigned long time) Line 133
Qt6Core.dll!QWaitCondition::wait(QMutex * mutex, QDeadlineTimer deadline) Line 144
[Inline Frame] Qt6Quick.dll!QSGRenderThreadEventQueue::takeEvent(bool) Line 204
[Inline Frame] Qt6Quick.dll!QSGRenderThread::processEventsAndWaitForMore() Line 831
Qt6Quick.dll!QSGRenderThread::run() Line 952
Qt6Core.dll!QThreadPrivate::start(void * arg) Line 292
kernel32.dll!BaseThreadInitThunk()
ntdll.dll!RtlUserThreadStart()
So, it seems (I'm not sure btw, never saw the code) that QSGRenderThreadEventQueue::takeEvent waits for a resource locked by QSGThreadedRenderLoop::polishAndSync (or someone who called it) while QSGThreadedRenderLoop::polishAndSync waits for another one locked by QSGRenderThreadEventQueue::takeEvent.
