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Details

Type: Bug
Resolution: Incomplete
Priority: Not Evaluated
Fix Version/s: None
Affects Version/s: 4.8.4
Component/s: Core: Event loop
Labels:
None
Environment:
Windows 7 x64, Windows XP x86, Windows Server 2003 x64, release & debug Visual Studio 2010 SP1

Description

Similar issue: https://bugreports.qt-project.org/browse/QTBUG-28513

I'm seeing a weird issue in Qt 4.8.4 Visual Studio 2010 SP1. The symptoms - QEventDispatcher goes into an infinite loop while processing WM_QT_SENDPOSTEDEVENTS. This was first not reproducible on all computers I'm testing on, but using remote debugging, I tracked something weird in qeventdispatcher_win.cpp on some of them and managed to actually catch this on all machines later that day.

entry: bool QEventDispatcherWin32::processEvents(QEventLoop::ProcessEventsFlags flags)
726:         while (!d->interrupt) {
742:             haveMessage = PeekMessage(&msg, 0, 0, 0, PM_REMOVE);
783:             if (d->internalHwnd == msg.hwnd && msg.message == WM_QT_SENDPOSTEDEVENTS) {
784:                 if (seenWM_QT_SENDPOSTEDEVENTS) {
790:                 seenWM_QT_SENDPOSTEDEVENTS = true;
807:         if (!filterEvent(&msg)) {
808:             TranslateMessage(&msg);
726:         while (!d->interrupt) {
742:             haveMessage = PeekMessage(&msg, 0, 0, 0, PM_REMOVE);
783:             if (d->internalHwnd == msg.hwnd && msg.message == WM_QT_SENDPOSTEDEVENTS) {
784:                 if (seenWM_QT_SENDPOSTEDEVENTS) {
787:                     needWM_QT_SENDPOSTEDEVENTS = true;
788:                     continue;
726:         while (!d->interrupt) {
742:             haveMessage = PeekMessage(&msg, 0, 0, 0, PM_REMOVE);
838: } while (canWait);
845: if (needWM_QT_SENDPOSTEDEVENTS)
846:     PostMessage(d->internalHwnd, WM_QT_SENDPOSTEDEVENTS, 0, 0);
848: exit: return retVal;
708: entry: bool QEventDispatcherWin32::processEvents(QEventLoop::ProcessEventsFlags flags)
726:         while (!d->interrupt) {
742:             haveMessage = PeekMessage(&msg, 0, 0, 0, PM_REMOVE);
783:             if (d->internalHwnd == msg.hwnd && msg.message == WM_QT_SENDPOSTEDEVENTS) {
784:                 if (seenWM_QT_SENDPOSTEDEVENTS) {
790:                 seenWM_QT_SENDPOSTEDEVENTS = true;
807:         if (!filterEvent(&msg)) {
808:             TranslateMessage(&msg);
726:         while (!d->interrupt) {
742:             haveMessage = PeekMessage(&msg, 0, 0, 0, PM_REMOVE);
783:             if (d->internalHwnd == msg.hwnd && msg.message == WM_QT_SENDPOSTEDEVENTS) {
784:                 if (seenWM_QT_SENDPOSTEDEVENTS) {
787:                     needWM_QT_SENDPOSTEDEVENTS = true;
788:                     continue;
726:         while (!d->interrupt) {
742:             haveMessage = PeekMessage(&msg, 0, 0, 0, PM_REMOVE);
838: } while (canWait);
845: if (needWM_QT_SENDPOSTEDEVENTS)
846:     PostMessage(d->internalHwnd, WM_QT_SENDPOSTEDEVENTS, 0, 0);
848: exit: return retVal;

The message gets re-posted. The place that controls this checks if it's just been posted on line 783, just to be re-posted on line 846. I don't know the meaning of d->internalHwnd == msg.hwnd on line 783, though. It's clear that an infinite loop will arise, if you're posting it with d->internalHwnd on line 846.

This may affect both x64, x86 and x86 debug Qt libraries and seems to be related to ZeroTimerEvent. The event results in QApplication::notify, with receiver having its virtual function table pointing to QtWebKitd4.dll!WebCore::SharedTimerQt::metaObject(void)const. But, the window containing the web view has been long supposed to be closed (The close() method has already been called on it). In other words, closing the window containing a QWebView causes some timer go haywire under specific conditions.