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QEventDispatcherWin32: rework sending of posted events

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Since its initial implementation, QEventDispatcherWin32 manages a
delivery of the posted events from the window procedure through
WM_QT_SENDPOSTEDEVENTS message. That makes the implementation quite
difficult and unclear. As a result, posted events get stalled,
in case of using nested event loops or other recursion.

The proposed solution is to send posted events at the beginning of
processEvents() only once per iteration of the event loop. However,
in case of using a foreign event loop (e.g. by opening a native
modal dialog), we should leave the emission in the window procedure,
as we don't control its execution.

Task-number: QTBUG-74564
Change-Id: Ib7ce85b65405af6124823dda1451d1370aed9b1a
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>
This commit is contained in:
Alex Trotsenko 2019-03-25 18:05:14 +02:00
parent f239cd5797
commit 6a7cea64d2
2 changed files with 56 additions and 70 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

124
src/corelib/kernel/qeventdispatcher_win.cpp
View File

@ -82,8 +82,13 @@ extern uint qGlobalPostedEventsCount();
enum {
WM_QT_SOCKETNOTIFIER = WM_USER,
WM_QT_SENDPOSTEDEVENTS = WM_USER + 1,
WM_QT_ACTIVATENOTIFIERS = WM_USER + 2,
SendPostedEventsWindowsTimerId = ~1u
WM_QT_ACTIVATENOTIFIERS = WM_USER + 2
};
// WM_QT_SENDPOSTEDEVENTS message parameter
enum {
WMWP_QT_TOFOREIGNLOOP = 0,
WMWP_QT_FROMWAKEUP
};
class QEventDispatcherWin32Private;
@ -96,8 +101,8 @@ LRESULT QT_WIN_CALLBACK qt_internal_proc(HWND hwnd, UINT message, WPARAM wp, LPA
QEventDispatcherWin32Private::QEventDispatcherWin32Private()
: threadId(GetCurrentThreadId()), interrupt(false), internalHwnd(0),
getMessageHook(0), serialNumber(0), lastSerialNumber(0), sendPostedEventsWindowsTimerId(0),
wakeUps(0), activateNotifiersPosted(false), winEventNotifierActivatedEvent(NULL)
getMessageHook(0), wakeUps(0), activateNotifiersPosted(false),
winEventNotifierActivatedEvent(NULL)
{
}
@ -234,22 +239,20 @@ LRESULT QT_WIN_CALLBACK qt_internal_proc(HWND hwnd, UINT message, WPARAM wp, LPA
return 0;
}
case WM_TIMER:
if (d->sendPostedEventsWindowsTimerId == 0
|| wp != uint(d->sendPostedEventsWindowsTimerId)) {
Q_ASSERT(d != 0);
d->sendTimerEvent(wp);
return 0;
}
// we also use a Windows timer to send posted events when the message queue is full
Q_FALLTHROUGH();
case WM_QT_SENDPOSTEDEVENTS: {
const int localSerialNumber = d->serialNumber.load();
if (localSerialNumber != d->lastSerialNumber) {
d->lastSerialNumber = localSerialNumber;
q->sendPostedEvents();
}
Q_ASSERT(d != 0);
d->sendTimerEvent(wp);
return 0;
case WM_QT_SENDPOSTEDEVENTS:
Q_ASSERT(d != 0);
// Allow posting WM_QT_SENDPOSTEDEVENTS message.
d->wakeUps.store(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();
return 0;
}
} // switch (message)
return DefWindowProc(hwnd, message, wp, lp);
@ -272,39 +275,6 @@ LRESULT QT_WIN_CALLBACK qt_GetMessageHook(int code, WPARAM wp, LPARAM lp)
QEventDispatcherWin32 *q = qobject_cast<QEventDispatcherWin32 *>(QAbstractEventDispatcher::instance());
Q_ASSERT(q != 0);
if (wp == PM_REMOVE) {
if (q) {
MSG *msg = (MSG *) lp;
QEventDispatcherWin32Private *d = q->d_func();
const int localSerialNumber = d->serialNumber.load();
static const UINT mask = inputTimerMask();
if (HIWORD(GetQueueStatus(mask)) == 0) {
// no more input or timer events in the message queue, we can allow posted events to be sent normally now
if (d->sendPostedEventsWindowsTimerId != 0) {
// stop the timer to send posted events, since we now allow the WM_QT_SENDPOSTEDEVENTS message
KillTimer(d->internalHwnd, d->sendPostedEventsWindowsTimerId);
d->sendPostedEventsWindowsTimerId = 0;
}
(void) d->wakeUps.fetchAndStoreRelease(0);
if (localSerialNumber != d->lastSerialNumber
// if this message IS the one that triggers sendPostedEvents(), no need to post it again
&& (msg->hwnd != d->internalHwnd
|| msg->message != WM_QT_SENDPOSTEDEVENTS)) {
PostMessage(d->internalHwnd, WM_QT_SENDPOSTEDEVENTS, 0, 0);
}
} else if (d->sendPostedEventsWindowsTimerId == 0
&& localSerialNumber != d->lastSerialNumber) {
// start a special timer to continue delivering posted events while
// there are still input and timer messages in the message queue
d->sendPostedEventsWindowsTimerId = SetTimer(d->internalHwnd,
SendPostedEventsWindowsTimerId,
0, // we specify zero, but Windows uses USER_TIMER_MINIMUM
NULL);
// we don't check the return value of SetTimer()... if creating the timer failed, there's little
// we can do. we just have to accept that posted events will be starved
}
}
}
return q->d_func()->getMessageHook ? CallNextHookEx(0, code, wp, lp) : 0;
}
@ -559,9 +529,12 @@ bool QEventDispatcherWin32::processEvents(QEventLoop::ProcessEventsFlags flags)
d->interrupt.store(false);
emit awake();
// To prevent livelocks, send posted events once per iteration.
// QCoreApplication::sendPostedEvents() takes care about recursions.
sendPostedEvents();
bool canWait;
bool retVal = false;
bool seenWM_QT_SENDPOSTEDEVENTS = false;
bool needWM_QT_SENDPOSTEDEVENTS = false;
do {
DWORD waitRet = 0;
@ -615,14 +588,15 @@ bool QEventDispatcherWin32::processEvents(QEventLoop::ProcessEventsFlags flags)
(void) qt_GetMessageHook(0, PM_REMOVE, reinterpret_cast<LPARAM>(&msg));
if (d->internalHwnd == msg.hwnd && msg.message == WM_QT_SENDPOSTEDEVENTS) {
if (seenWM_QT_SENDPOSTEDEVENTS) {
// when calling processEvents() "manually", we only want to send posted
// events once
needWM_QT_SENDPOSTEDEVENTS = true;
continue;
// Set result to 'true', if the message was sent by wakeUp().
if (msg.wParam == WMWP_QT_FROMWAKEUP) {
d->wakeUps.store(0);
retVal = true;
}
seenWM_QT_SENDPOSTEDEVENTS = true;
} else if (msg.message == WM_TIMER) {
needWM_QT_SENDPOSTEDEVENTS = true;
continue;
}
if (msg.message == WM_TIMER) {
// 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) {
@ -639,10 +613,22 @@ bool QEventDispatcherWin32::processEvents(QEventLoop::ProcessEventsFlags flags)
}
if (!filterNativeEvent(QByteArrayLiteral("windows_generic_MSG"), &msg, 0)) {
// Post WM_QT_SENDPOSTEDEVENTS before calling external code,
// as it can start a foreign event loop.
if (needWM_QT_SENDPOSTEDEVENTS) {
needWM_QT_SENDPOSTEDEVENTS = false;
PostMessage(d->internalHwnd, WM_QT_SENDPOSTEDEVENTS,
WMWP_QT_TOFOREIGNLOOP, 0);
}
TranslateMessage(&msg);
DispatchMessage(&msg);
}
} else if (waitRet - WAIT_OBJECT_0 < nCount) {
if (needWM_QT_SENDPOSTEDEVENTS) {
needWM_QT_SENDPOSTEDEVENTS = false;
PostMessage(d->internalHwnd, WM_QT_SENDPOSTEDEVENTS,
WMWP_QT_TOFOREIGNLOOP, 0);
}
activateEventNotifiers();
} else {
// nothing todo so break
@ -660,19 +646,20 @@ bool QEventDispatcherWin32::processEvents(QEventLoop::ProcessEventsFlags flags)
waitRet = MsgWaitForMultipleObjectsEx(nCount, pHandles, INFINITE, QS_ALLINPUT, MWMO_ALERTABLE | MWMO_INPUTAVAILABLE);
emit awake();
if (waitRet - WAIT_OBJECT_0 < nCount) {
if (needWM_QT_SENDPOSTEDEVENTS) {
needWM_QT_SENDPOSTEDEVENTS = false;
PostMessage(d->internalHwnd, WM_QT_SENDPOSTEDEVENTS,
WMWP_QT_TOFOREIGNLOOP, 0);
}
activateEventNotifiers();
retVal = true;
}
}
} while (canWait);
if (!seenWM_QT_SENDPOSTEDEVENTS && (flags & QEventLoop::EventLoopExec) == 0) {
// when called "manually", always send posted events
sendPostedEvents();
}
if (needWM_QT_SENDPOSTEDEVENTS)
PostMessage(d->internalHwnd, WM_QT_SENDPOSTEDEVENTS, 0, 0);
PostMessage(d->internalHwnd, WM_QT_SENDPOSTEDEVENTS,
WMWP_QT_TOFOREIGNLOOP, 0);
return retVal;
}
@ -1016,10 +1003,11 @@ int QEventDispatcherWin32::remainingTime(int timerId)
void QEventDispatcherWin32::wakeUp()
{
Q_D(QEventDispatcherWin32);
d->serialNumber.ref();
if (d->internalHwnd && d->wakeUps.testAndSetAcquire(0, 1)) {
// post a WM_QT_SENDPOSTEDEVENTS to this thread if there isn't one already pending
PostMessage(d->internalHwnd, WM_QT_SENDPOSTEDEVENTS, 0, 0);
if (!PostMessage(d->internalHwnd, WM_QT_SENDPOSTEDEVENTS,
WMWP_QT_FROMWAKEUP, 0))
qErrnoWarning("QEventDispatcherWin32::wakeUp: Failed to post a message");
}
}

2
src/corelib/kernel/qeventdispatcher_win_p.h
View File

@ -172,8 +172,6 @@ public:
HHOOK getMessageHook;
// for controlling when to send posted events
QAtomicInt serialNumber;
int lastSerialNumber, sendPostedEventsWindowsTimerId;
QAtomicInt wakeUps;
// timers