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QEventDispatcherWin32: fix posted events delivering

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To avoid livelocks, posted events should be delivered when all pending
messages have been processed, and the thread's message queue becomes
empty. Although the logic of the previous patch is correct, it turned
out that determining the moment when the message queue is really empty
is not so simple. It is worth noting that the GetQueueStatus function
sometimes reports unexpected results due to internal filtering and
processing. Indeed, Windows docs say that "the return value from
GetQueueStatus should be considered only a hint as to whether
GetMessage or PeekMessage should be called". Thus, we cannot rely on
GetQueueStatus in unambiguous logic inside the qt_GetMessageHook.

To solve the problem, this patch introduces a guard timer which
guarantees low priority processing for posted events in foreign loop.
The wakeUps flag reset logic has also been changed to provide clearer
synchronization of the Qt internal loop.

Fixes: QTBUG-82701
Fixes: QTBUG-83151
Change-Id: I33d5001a40d2a4879ef4eb878c09bc1c0616e289
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>
This commit is contained in:
Alex Trotsenko 2020-03-18 20:04:47 +02:00 committed by Volker Hilsheimer
parent 9834536cfa
commit e0d80167c1
2 changed files with 49 additions and 32 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

80
src/corelib/kernel/qeventdispatcher_win.cpp
View File

@ -84,10 +84,8 @@ enum {
WM_QT_ACTIVATENOTIFIERS = WM_USER + 2
};
// WM_QT_SENDPOSTEDEVENTS message parameter
enum {
WMWP_QT_TOFOREIGNLOOP = 0,
WMWP_QT_FROMWAKEUP
SendPostedEventsTimerId = ~1u
};
class QEventDispatcherWin32Private;
@ -100,8 +98,8 @@ LRESULT QT_WIN_CALLBACK qt_internal_proc(HWND hwnd, UINT message, WPARAM wp, LPA
QEventDispatcherWin32Private::QEventDispatcherWin32Private()
: threadId(GetCurrentThreadId()), interrupt(false), internalHwnd(0),
getMessageHook(0), wakeUps(0), activateNotifiersPosted(false),
winEventNotifierActivatedEvent(NULL)
getMessageHook(0), sendPostedEventsTimerId(0), wakeUps(0),
activateNotifiersPosted(false), winEventNotifierActivatedEvent(NULL)
{
}
@ -129,6 +127,18 @@ void WINAPI QT_WIN_CALLBACK qt_fast_timer_proc(uint timerId, uint /*reserved*/,
QCoreApplication::postEvent(t->dispatcher, new QTimerEvent(t->timerId));
}
static inline UINT inputQueueMask()
{
UINT result = QS_ALLEVENTS;
// QTBUG 28513, QTBUG-29097, QTBUG-29435: QS_TOUCH, QS_POINTER became part of
// QS_INPUT in Windows Kit 8. They should not be used when running on pre-Windows 8.
#if WINVER > 0x0601
if (QOperatingSystemVersion::current() < QOperatingSystemVersion::Windows8)
result &= ~(QS_TOUCH | QS_POINTER);
#endif // WINVER > 0x0601
return result;
}
LRESULT QT_WIN_CALLBACK qt_internal_proc(HWND hwnd, UINT message, WPARAM wp, LPARAM lp)
{
if (message == WM_NCCREATE)
@ -240,47 +250,39 @@ LRESULT QT_WIN_CALLBACK qt_internal_proc(HWND hwnd, UINT message, WPARAM wp, LPA
case WM_TIMER:
Q_ASSERT(d != 0);
d->sendTimerEvent(wp);
if (wp == d->sendPostedEventsTimerId)
q->sendPostedEvents();
else
d->sendTimerEvent(wp);
return 0;
case WM_QT_SENDPOSTEDEVENTS:
Q_ASSERT(d != 0);
// We send posted events manually, if the window procedure was invoked
// by the foreign event loop (e.g. from the native modal dialog).
q->sendPostedEvents();
// Skip sending, if the message queue is not empty.
// sendPostedEventsTimer will deliver posted events later.
static const UINT mask = inputQueueMask();
if (HIWORD(GetQueueStatus(mask)) == 0)
q->sendPostedEvents();
return 0;
} // switch (message)
return DefWindowProc(hwnd, message, wp, lp);
}
static inline UINT inputQueueMask()
{
UINT result = QS_ALLEVENTS;
// QTBUG 28513, QTBUG-29097, QTBUG-29435: QS_TOUCH, QS_POINTER became part of
// QS_INPUT in Windows Kit 8. They should not be used when running on pre-Windows 8.
#if WINVER > 0x0601
if (QOperatingSystemVersion::current() < QOperatingSystemVersion::Windows8)
result &= ~(QS_TOUCH | QS_POINTER);
#endif // WINVER > 0x0601
return result;
}
LRESULT QT_WIN_CALLBACK qt_GetMessageHook(int code, WPARAM wp, LPARAM lp)
{
QEventDispatcherWin32 *q = qobject_cast<QEventDispatcherWin32 *>(QAbstractEventDispatcher::instance());
Q_ASSERT(q != 0);
QEventDispatcherWin32Private *d = q->d_func();
MSG *msg = reinterpret_cast<MSG *>(lp);
static const UINT mask = inputQueueMask();
if (HIWORD(GetQueueStatus(mask)) == 0 && wp == PM_REMOVE) {
// Allow posting WM_QT_SENDPOSTEDEVENTS message.
d->wakeUps.storeRelaxed(0);
if (!(msg->hwnd == d->internalHwnd && msg->message == WM_QT_SENDPOSTEDEVENTS)) {
PostMessage(d->internalHwnd, WM_QT_SENDPOSTEDEVENTS,
WMWP_QT_TOFOREIGNLOOP, 0);
}
if (msg->hwnd == d->internalHwnd && msg->message == WM_QT_SENDPOSTEDEVENTS
&& wp == PM_REMOVE && d->sendPostedEventsTimerId == 0) {
// Start a timer to deliver posted events when the message queue is emptied.
d->sendPostedEventsTimerId = SetTimer(d->internalHwnd, SendPostedEventsTimerId,
USER_TIMER_MINIMUM, NULL);
}
return d->getMessageHook ? CallNextHookEx(0, code, wp, lp) : 0;
}
@ -571,12 +573,15 @@ bool QEventDispatcherWin32::processEvents(QEventLoop::ProcessEventsFlags flags)
}
if (haveMessage) {
if (d->internalHwnd == msg.hwnd && msg.message == WM_QT_SENDPOSTEDEVENTS) {
// Set result to 'true', if the message was sent by wakeUp().
if (msg.wParam == WMWP_QT_FROMWAKEUP)
retVal = true;
// Set result to 'true' because the message was sent by wakeUp().
retVal = true;
continue;
}
if (msg.message == WM_TIMER) {
// Skip timer event intended for use inside foreign loop.
if (d->internalHwnd == msg.hwnd && msg.wParam == d->sendPostedEventsTimerId)
continue;
// avoid live-lock by keeping track of the timers we've already sent
bool found = false;
for (int i = 0; !found && i < processedTimers.count(); ++i) {
@ -964,8 +969,7 @@ void QEventDispatcherWin32::wakeUp()
Q_D(QEventDispatcherWin32);
if (d->internalHwnd && d->wakeUps.testAndSetAcquire(0, 1)) {
// post a WM_QT_SENDPOSTEDEVENTS to this thread if there isn't one already pending
if (!PostMessage(d->internalHwnd, WM_QT_SENDPOSTEDEVENTS,
WMWP_QT_FROMWAKEUP, 0))
if (!PostMessage(d->internalHwnd, WM_QT_SENDPOSTEDEVENTS, 0, 0))
qErrnoWarning("QEventDispatcherWin32::wakeUp: Failed to post a message");
}
}
@ -1007,6 +1011,10 @@ void QEventDispatcherWin32::closingDown()
if (d->getMessageHook)
UnhookWindowsHookEx(d->getMessageHook);
d->getMessageHook = 0;
if (d->sendPostedEventsTimerId != 0)
KillTimer(d->internalHwnd, d->sendPostedEventsTimerId);
d->sendPostedEventsTimerId = 0;
}
bool QEventDispatcherWin32::event(QEvent *e)
@ -1048,6 +1056,14 @@ bool QEventDispatcherWin32::event(QEvent *e)
void QEventDispatcherWin32::sendPostedEvents()
{
Q_D(QEventDispatcherWin32);
if (d->sendPostedEventsTimerId != 0)
KillTimer(d->internalHwnd, d->sendPostedEventsTimerId);
d->sendPostedEventsTimerId = 0;
// Allow posting WM_QT_SENDPOSTEDEVENTS message.
d->wakeUps.storeRelaxed(0);
QCoreApplicationPrivate::sendPostedEvents(0, 0, d->threadData);
}

1
src/corelib/kernel/qeventdispatcher_win_p.h
View File

@ -170,6 +170,7 @@ public:
HHOOK getMessageHook;
// for controlling when to send posted events
UINT_PTR sendPostedEventsTimerId;
QAtomicInt wakeUps;
// timers