Details
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Bug
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Resolution: Incomplete
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Not Evaluated
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None
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5.12.5
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None
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Linux/Wayland
Description
Hi,
the stacktrace is from my own project, but it highly looks like my main (render) thread is frozen because of a recursive lock in QWaylandWindow::waitForFrameSync(int).
It is noteworthy that in this stack trace, for some reason my application's TerminalWindow::event(QEvent*) is also recursively invoked, which I am not sure that this is intended, however, in the inner event handling, the mutex is already locked by the outer call to waitForFrameSync() in the wayland code base, hence the freeze.
It looks like a bug in the QtWayland code base, that's why I am posting it here. I hope however, that I am wrong and it's my fault instead. 
- OS: Ubuntu 19.10, with Qt 5.12.5; I upgraded from 19.04 (Qt 5.12.4) in the hopes to get this issue fixed.
- Window Manager: Sway
- running the app in with xcb backend works just fine.
The following snipped is the stack trace as captured at SIGINT:
46: syscall (syscall.S:38) 45: _q_futex (qfutex_p.h:92) 44: futexWait<QBasicAtomicPointer<QMutexData> > (qfutex_p.h:107) 43: lockInternal_helper<false> (qmutex_linux.cpp:142) 42: QBasicMutex::lockInternal() (qmutex_linux.cpp:159) 41: ??? (in /usr/lib/x86_64-linux-gnu/valgrind/vgpreload_helgrind-amd64-linux.so) 40: QMutexLocker (qmutex.h:206) 39: QtWaylandClient::QWaylandWindow::waitForFrameSync(int) (qwaylandwindow.cpp:664) 38: QtWaylandClient::QWaylandGLContext::swapBuffers(QPlatformSurface*) (qwaylandglcontext.cpp:566) 37: QOpenGLContext::swapBuffers(QSurface*) (qopenglcontext.cpp:1112) 36: QOpenGLWindowPrivate::flush(QRegion const&) (qopenglwindow.cpp:335) 35: doFlush (qpaintdevicewindow_p.h:105) 34: handleUpdateEvent (qpaintdevicewindow_p.h:112) 33: QPaintDeviceWindow::event(QEvent*) (qpaintdevicewindow.cpp:202) 32: contour::TerminalWindow::event(QEvent*) (TerminalWindow.cpp:581) 31: QCoreApplication::notifyInternal2(QObject*, QEvent*) (qcoreapplication.cpp:1088) 30: QPlatformWindow::deliverUpdateRequest() (qplatformwindow.cpp:793) 29: operator() (qwaylandwindow.cpp:650) 28: operator() (qwaylandwindow.cpp:641) 27: QtWaylandClient::QWaylandWindow::handleFrameCallback() (qwaylandwindow.cpp:656) 26: ffi_call_unix64 (unix64.S:101) 25: ffi_call_int (ffi64.c:669) 24: wl_closure_invoke (connection.c:1018) 23: dispatch_event.isra.0 (wayland-client.c:1445) 22: dispatch_queue (wayland-client.c:1591) 21: wl_display_dispatch_queue_pending (wayland-client.c:1833) 20: QtWaylandClient::QWaylandDisplay::dispatchQueueWhile(wl_event_queue*, std::function<bool ()>, int) (qwaylanddisplay.cpp:225) 19: QtWaylandClient::QWaylandWindow::waitForFrameSync(int) (qwaylandwindow.cpp:669) 18: QtWaylandClient::QWaylandGLContext::swapBuffers(QPlatformSurface*) (qwaylandglcontext.cpp:566) 17: QOpenGLContext::swapBuffers(QSurface*) (qopenglcontext.cpp:1112) 16: QOpenGLWindowPrivate::flush(QRegion const&) (qopenglwindow.cpp:335) 15: doFlush (qpaintdevicewindow_p.h:105) 14: QPaintDeviceWindow::exposeEvent(QExposeEvent*) (qpaintdevicewindow.cpp:189) 13: QWindow::event(QEvent*) (qwindow.cpp:2347) 12: QPaintDeviceWindow::event(QEvent*) (qpaintdevicewindow.cpp:206) 11: contour::TerminalWindow::event(QEvent*) (TerminalWindow.cpp:581) 10: QCoreApplication::notifyInternal2(QObject*, QEvent*) (qcoreapplication.cpp:1088) 9: QGuiApplicationPrivate::processExposeEvent(QWindowSystemInterfacePrivate::ExposeEvent*) (qguiapplication.cpp:3071) 8: QGuiApplicationPrivate::processWindowSystemEvent(QWindowSystemInterfacePrivate::WindowSystemEvent*) (qguiapplication.cpp:1907) 7: QWindowSystemInterface::sendWindowSystemEvents(QFlags<QEventLoop::ProcessEventsFlag>) (qwindowsysteminterface.cpp:1151) 6: userEventSourceDispatch(_GSource*, int (*)(void*), void*) (in /usr/lib/x86_64-linux-gnu/libQt5WaylandClient.so.5.12.5) 5: g_main_context_dispatch (in /usr/lib/x86_64-linux-gnu/libglib-2.0.so.0.6400.1) 4: ??? (in /usr/lib/x86_64-linux-gnu/libglib-2.0.so.0.6400.1) 3: g_main_context_iteration (in /usr/lib/x86_64-linux-gnu/libglib-2.0.so.0.6400.1) 2: QEventDispatcherGlib::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) (qeventdispatcher_glib.cpp:422) 1: QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) (qeventloop.cpp:225) 1378: QCoreApplication::exec() (qcoreapplication.cpp:1389) 1: main (main.cpp:77)