Details
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Bug
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Resolution: Invalid
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P1: Critical
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None
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5.12.9, 5.12.10, 6.4.2
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None
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Windows 10, x64
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Windows
Description
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**Edit** Some of our users can't start app at all due to this bug.
I think, this bug affects all the desktop applications using QML under Windows, in case there A-Volute's Sonic Studio is installed on the user's PC.
This software is installed by e.g. Asus and Dell.
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One of our users reported this:
"Another bug which usually occurs is that when I hibernate my system and then resume the FDM will enter the non-responding state. I usually close it via task manager and then restart."
He sent me the process dump. I've analyzed it and found the culprit, and also the possible reason of the bug.
First of all, the main thread hangs here:
ntdll.dll!NtWaitForSingleObject () KERNELBASE.dll!WaitForSingleObjectEx () Qt5Core.dll!QWaitCondition::wait(QMutex * mutex, unsigned long time) Line 178 Qt5Quick.dll!QSGThreadedRenderLoop::polishAndSync(QSGThreadedRenderLoop::Window * w, bool inExpose) Line 1218 Qt5Quick.dll!QSGThreadedRenderLoop::handleExposure(QQuickWindow * window) Line 1012 Qt5Gui.dll!QWindow::event(QEvent * ev) Line 2365 Qt5Widgets.dll!QApplicationPrivate::notify_helper(QObject * receiver, QEvent * e) Line 3702 Qt5Widgets.dll!QApplication::notify(QObject * receiver, QEvent * e) Line 3529 Qt5Core.dll!QCoreApplication::notifyInternal2(QObject * receiver, QEvent * event) Line 1088 Qt5Gui.dll!QGuiApplicationPrivate::processExposeEvent(QWindowSystemInterfacePrivate::ExposeEvent * e) Line 3078 Qt5Gui.dll!QWindowSystemInterface::sendWindowSystemEvents(QFlags<enum QEventLoop::ProcessEventsFlag> flags) Line 1163 Qt5Gui.dll!QWindowSystemInterface::flushWindowSystemEvents(QFlags<enum QEventLoop::ProcessEventsFlag> flags) Line 1123 qwindows.dll!00007ff876a1668b() qwindows.dll!00007ff876a235de() qwindows.dll!00007ff876a243ab() user32.dll!UserCallWinProcCheckWow() user32.dll!DispatchClientMessage() user32.dll!__fnDWORD () ntdll.dll!KiUserCallbackDispatcherContinue () win32u.dll!NtUserDispatchMessage () user32.dll!DispatchMessageWorker() Qt5Core.dll!QEventDispatcherWin32::processEvents(QFlags<enum QEventLoop::ProcessEventsFlag> flags) Line 640 qwindows.dll!00007ff876a735b9() Qt5Core.dll!QEventLoop::exec(QFlags<enum QEventLoop::ProcessEventsFlag> flags) Line 225 Qt5Core.dll!QCoreApplication::exec() Line 1389 fdm.exe!main () fdm.exe!WinMain () fdm.exe!__scrt_common_main_seh() Line 288 kernel32.dll!BaseThreadInitThunk () ntdll.dll!RtlUserThreadStart ()
Here it's seen that QSGThreadedRenderLoop::polishAndSync hangs waiting for a mutex (deadlock). Why? I don't have sources of Qt (did not look into them) and neither I have Windows sources 
. But... Here is the another thread:
win32u.dll!NtUserEnumDisplayMonitors () d3d9.dll!CEnum::GetAdapterMonitor() NahimicOSD.dll!00007ff889e4ef5b() NahimicOSD.dll!00007ff889e4d755() NahimicOSD.dll!00007ff889e4ad52() gdi32full.dll!SwapBuffers () Qt5Gui.dll!QOpenGLContext::swapBuffers(QSurface * surface) Line 1112 Qt5Quick.dll!QSGRenderThread::syncAndRender() Line 653 Qt5Quick.dll!QSGRenderThread::run() Line 733 Qt5Core.dll!QThreadPrivate::start(void * arg) Line 405 kernel32.dll!BaseThreadInitThunk () ntdll.dll!RtlUserThreadStart ()
Here I suspect that QSGRenderThread::syncAndRender locked that mutex and then called NtUserEnumDisplayMonitors. And it seems that this NtUserEnumDisplayMonitors hangs too. I think it somehow waits for Windows UI functions to release their locks (main thread is calling DispatchMessage).
So, main thread locks Windows's internal UI objects and then attempts to lock some SG Render's object. In the same time another thread already locked that SG Render's object and tries to lock UI object. Classic dead lock.
Here is another report, but it was closed with "Incomplete" state: https://bugreports.qt.io/browse/QTBUG-42162