Cocoa: Fix several issues with the event dispatcher

Autotest: qcoreapplication, qapplication, qtimer
qwidget_window, qwidget

Issue 1: stacking order of modal windows was not
working correctly. With this patch, we remove the
need for rebuilding modal sessions all the time,
and when we do, we rebuild them all in the correct
order.

Issue 2: When running the event processor manually
(that is, just calling processEvents in a loop), we
sometimes spendt 100% cpu if a window was pending to
become modal. The reason was that we need to keep
reposting the QCocoaRequestModal event until we
could block the calling thread (that is, one of
the exec flags was given to processEvents). With this
patch, the need for posting QCocoaRequestModal is
completly removed in favor of an 'interrupt'
approach instead.

Issue 3: If using Qt as a plugin, or just add widget
to a native cocoa application, it would often lead
to closing down the application. The reason is that
the event dispatcher needs to restart [NSApp run]
now and then. But this approach fails if Qt was not
the code that started [NSApp run] in the first place.
This patch removes the need to restart NSApp in this
situation, at the cost of modal windows not beeing
modal if Qt is not spinning the event dispatcher.
Normal QDialog::exec etc will always work.

6 files changed, 308 insertions, 193 deletions

diff --git a/src/gui/kernel/qapplication.cpp b/src/gui/kernel/qapplication.cpp
index fea3e2dae..df85809ff 100644
--- a/src/gui/kernel/qapplication.cpp
+++ b/src/gui/kernel/qapplication.cpp
@@ -2311,10 +2311,6 @@ bool QApplication::event(QEvent *e)
         } else if (te->timerId() == d->toolTipFallAsleep.timerId()) {
             d->toolTipFallAsleep.stop();
         }
-#ifdef QT_MAC_USE_COCOA
-    } else if (e->type() == QEvent::CocoaRequestModal) {
-        d->_q_runAppModalWindow();
-#endif
     }
     return QCoreApplication::event(e);
 }
diff --git a/src/gui/kernel/qapplication_mac.mm b/src/gui/kernel/qapplication_mac.mm
index 5b503b35d..0c1789293 100644
--- a/src/gui/kernel/qapplication_mac.mm
+++ b/src/gui/kernel/qapplication_mac.mm
@@ -1409,13 +1409,8 @@ void QApplicationPrivate::enterModal_sys(QWidget *widget)
     qt_button_down = 0;
 
 #ifdef QT_MAC_USE_COCOA
-    if (!qt_mac_is_macsheet(widget)) {
-        // Add a new, empty (null), NSModalSession to the stack.
-        // The next time we spin the event dispatcher, it will
-        // check the stack, and recurse into a modal session for it:
-        QCocoaModalSessionInfo info = {widget, 0};
-        QEventDispatcherMacPrivate::cocoaModalSessionStack.push(info);
-    }
+    if (!qt_mac_is_macsheet(widget))
+        QEventDispatcherMacPrivate::beginModalSession(widget);
 #endif
 }
 
@@ -1441,7 +1436,7 @@ void QApplicationPrivate::leaveModal_sys(QWidget *widget)
         }
 #ifdef QT_MAC_USE_COCOA
         if (!qt_mac_is_macsheet(widget))
-            QEventDispatcherMacPrivate::rebuildModalSessionStack(true);
+            QEventDispatcherMacPrivate::endModalSession(widget);
 #endif
     }
 #ifdef DEBUG_MODAL_EVENTS
@@ -1452,21 +1447,6 @@ void QApplicationPrivate::leaveModal_sys(QWidget *widget)
         qt_event_request_menubarupdate();
 }
 
-#if defined(QT_MAC_USE_COCOA)
-void QApplicationPrivate::_q_runAppModalWindow()
-{
-    if (QEventDispatcherMacPrivate::blockCocoaRequestModal) {
-        // Just postpone the event until the event dispatcher tells
-        // us (by releasing the block) that it is OK to recurse into
-        // a new event loop for our non-execing modal window:
-        qApp->postEvent(qApp, new QEvent(QEvent::CocoaRequestModal));
-    } else {
-        // Recurse into a new event loop for the current app modal window:
-        threadData->eventDispatcher->processEvents(QEventLoop::DialogExec);
-    }
-}
-#endif
-
 QWidget *QApplicationPrivate::tryModalHelper_sys(QWidget *top)
 {
 #ifndef QT_MAC_USE_COCOA
diff --git a/src/gui/kernel/qapplication_p.h b/src/gui/kernel/qapplication_p.h
index c90ebfef1..5d409f47b 100644
--- a/src/gui/kernel/qapplication_p.h
+++ b/src/gui/kernel/qapplication_p.h
@@ -484,12 +484,6 @@ public:
     void _q_alertTimeOut();
     QHash<QWidget *, QTimer *> alertTimerHash;
 #endif
-#if defined(QT_MAC_USE_COCOA)
-    void _q_runAppModalWindow();
-#endif
-#if defined(QT_MAC_USE_COCOA)
-    void _q_runModalWindow();
-#endif
 #ifndef QT_NO_STYLE_STYLESHEET
     static QString styleSheet;
 #endif
diff --git a/src/gui/kernel/qeventdispatcher_mac.mm b/src/gui/kernel/qeventdispatcher_mac.mm
index 2e454790b..efe6375a1 100644
--- a/src/gui/kernel/qeventdispatcher_mac.mm
+++ b/src/gui/kernel/qeventdispatcher_mac.mm
@@ -497,6 +497,40 @@ static bool IsMouseOrKeyEvent( NSEvent* event )
 }
 #endif
 
+static inline void qt_mac_waitForMoreEvents()
+{
+#ifndef QT_MAC_USE_COCOA
+    while(CFRunLoopRunInMode(kCFRunLoopDefaultMode, 1.0e20, true) == kCFRunLoopRunTimedOut);
+#else
+    // If no event exist in the cocoa event que, wait
+    // (and free up cpu time) until at least one event occur.
+    // This implementation is a bit on the edge, but seems to
+    // work fine:
+    NSEvent* event = [NSApp nextEventMatchingMask:NSAnyEventMask
+        untilDate:[NSDate distantFuture]
+        inMode:NSDefaultRunLoopMode
+        dequeue:YES];
+    if (event)
+        [NSApp postEvent:event atStart:YES];
+#endif
+}
+
+#ifdef QT_MAC_USE_COCOA
+static inline void qt_mac_waitForMoreModalSessionEvents()
+{
+    // If no event exist in the cocoa event que, wait
+    // (and free up cpu time) until at least one event occur.
+    // This implementation is a bit on the edge, but seems to
+    // work fine:
+    NSEvent* event = [NSApp nextEventMatchingMask:NSAnyEventMask
+        untilDate:[NSDate distantFuture]
+        inMode:NSModalPanelRunLoopMode
+        dequeue:YES];
+    if (event)
+        [NSApp postEvent:event atStart:YES];
+}
+#endif
+
 bool QEventDispatcherMac::processEvents(QEventLoop::ProcessEventsFlags flags)
 {
     Q_D(QEventDispatcherMac);
@@ -515,55 +549,42 @@ bool QEventDispatcherMac::processEvents(QEventLoop::ProcessEventsFlags flags)
         QMacCocoaAutoReleasePool pool;
         NSEvent* event = 0;
 
-        if (flags & QEventLoop::DialogExec || flags & QEventLoop::EventLoopExec) {
-            // The point of the CocoaRequestModal event is to make sure that a
-            // non-execed app modal window recurses into it's own dialog exec
-            // once cocoa is spinning the event loop for us (e.g on top of [NSApp run]).
-            // We expect only one event to notify us about this, regardless of how many
-            // widgets that are waiting to be modal. So we remove all other pending
-            // events, if any. And since cocoa will now take over event processing for us,
-            // we allow new app modal widgets to recurse on top of us, hence the release of
-            // the block:
-            QBoolBlocker block(d->blockCocoaRequestModal, false);
-            QCoreApplication::removePostedEvents(qApp, QEvent::CocoaRequestModal);
-
-            if (NSModalSession session = d->activeModalSession())
-                while ([NSApp runModalSession:session] == NSRunContinuesResponse) {
-                    // runModalSession will not wait for events, so we do it
-                    // ourselves (otherwise we would spend 100% CPU inside this loop):
-                    event = [NSApp nextEventMatchingMask:NSAnyEventMask
-                        untilDate:[NSDate distantFuture] inMode:NSModalPanelRunLoopMode dequeue:YES];
-                    if (event)
-                        [NSApp postEvent:event atStart:YES];
-                }
-            else
+        // If Qt is used as a plugin, or just added into a native cocoa
+        // application, we should not run or stop NSApplication;
+        // This will be done from outside Qt.
+        // And if processEvents is called manually (rather than from QEventLoop), we
+        // cannot enter a tight loop and block the call, but instead return after one flush:
+        bool canExec_3rdParty = d->nsAppRunCalledByQt || ![NSApp isRunning];
+        bool canExec_Qt = flags & QEventLoop::DialogExec || flags & QEventLoop::EventLoopExec;
+
+        if (canExec_Qt && canExec_3rdParty) {
+            // We can use exec-mode, meaning that we can stay in a tight loop until
+            // interrupted. This is mostly an optimization, but it also allow us
+            // to use [NSApp run], which is the recommended way of running applications
+            // in cocoa. [NSApp run] should be called at least once for any cocoa app.
+            if (NSModalSession session = d->currentModalSession()) {
+                QBoolBlocker execGuard(d->currentExecIsNSAppRun, false);
+                while (!d->interrupt && [NSApp runModalSession:session] == NSRunContinuesResponse)
+                    qt_mac_waitForMoreModalSessionEvents();
+            } else {
+                d->nsAppRunCalledByQt = true;
+                QBoolBlocker execGuard(d->currentExecIsNSAppRun, true);
                 [NSApp run];
-
-            d->rebuildModalSessionStack(false);
+            }
             retVal = true;
         } else do {
-            // Since we now are going to spin the event loop just _one_ round
-            // we need to block all incoming CocoaRequestModal events to ensure
-            // that we don't recurse into a new exec-ing event loop while doing
-            // so (and as such, 'hang' the thread inside the recursion):
-            QBoolBlocker block(d->blockCocoaRequestModal, true);
+            // INVARIANT: We cannot block the thread (and run in a tight loop).
+            // Instead we will process all current pending events and return.
             bool mustRelease = false;
 
             if (!(flags & QEventLoop::ExcludeUserInputEvents) && !d->queuedUserInputEvents.isEmpty()) {
-                // process a pending user input event
+                // Process a pending user input event
                 mustRelease = true;
                 event = static_cast<NSEvent *>(d->queuedUserInputEvents.takeFirst());
             } else {
-                if (NSModalSession session = d->activeModalSession()) {
-                    // There's s a modal widget showing, run it's session:
-                    if (flags & QEventLoop::WaitForMoreEvents) {
-                        // Wait for at least one event
-                        // before spinning the session:
-                        event = [NSApp nextEventMatchingMask:NSAnyEventMask
-                            untilDate:[NSDate distantFuture] inMode:NSModalPanelRunLoopMode dequeue:YES];
-                        if (event)
-                            [NSApp postEvent:event atStart:YES];
-                    }
+                if (NSModalSession session = d->currentModalSession()) {
+                    if (flags & QEventLoop::WaitForMoreEvents)
+                        qt_mac_waitForMoreModalSessionEvents();
                     [NSApp runModalSession:session];
                     retVal = true;
                     break;
@@ -634,41 +655,35 @@ bool QEventDispatcherMac::processEvents(QEventLoop::ProcessEventsFlags flags)
                 && (flags & QEventLoop::WaitForMoreEvents));
         if (canWait) {
             // INVARIANT: We haven't processed any events yet. And we're told
-            // to stay inside this function until at least one event is processed
-            // (WaitForMoreEvents). So we wait on the window server:
-#ifndef QT_MAC_USE_COCOA
-            while(CFRunLoopRunInMode(kCFRunLoopDefaultMode, 1.0e20, true) == kCFRunLoopRunTimedOut);
-#else
-            QMacCocoaAutoReleasePool pool;
-            NSEvent *manualEvent = [NSApp nextEventMatchingMask:NSAnyEventMask
-                untilDate:[NSDate distantFuture] inMode:NSDefaultRunLoopMode
-                dequeue:YES];
-            if (manualEvent)
-                [NSApp sendEvent:manualEvent];
-#endif
+            // to stay inside this function until at least one event is processed.
+            qt_mac_waitForMoreEvents();
             flags &= ~QEventLoop::WaitForMoreEvents;
         } else {
-            // Done with event processing for now. Leave the function:
+            // Done with event processing for now.
+            // Leave the function:
             break;
         }
     }
 
-    // Because pending deffered-delete events are only sendt after
-    // returning from the loop level they were posted in, we schedule
-    // an extra wakup to force the _current_ run loop to process them (in
-    // case the application stands idle waiting for the delete event):
-    wakeUp();
+#ifdef QT_MAC_USE_COCOA
+    // In case we _now_ process events using [NSApp run], we need to stop it to
+    // ensure that:
+    //    1. the QEventLoop that called us is still executing, or
+    //    2. we have a modal session that needs to be spun instead.
+    // In case this is a plain call to processEvents (perhaps from a loop) 
+    // from the application (rather than from a QEventLoop), we delay the
+    // interrupting until we/ actually enter a lower loop level (hence the
+    // deffered delete of the object below):
+    QtMacInterruptDispatcherHelp::interruptLater();
+#endif
 
-    if (d->interrupt){
-        // We restart NSApplication by first stopping it, and then call 'run'
-        // again (NSApplication is actually already stopped, hence the need
-        // for a restart, but calling stop again will also make the call
-        // return from the current recursion). When the call returns to
-        // QEventLoop (mind, not from this recursion, but from the one we're
-        // about to stop), it will just call QEventDispatcherMac::processEvents()
-        // again.
+    if (d->interrupt) {
+        // We should continue to leave all recursion to processEvents until
+        // processEvents is called again (e.g. from a QEventLoop that 
+        // was not yet told to quit:
         interrupt();
     }
+
     return retVal;
 }
 
@@ -700,104 +715,169 @@ bool QEventDispatcherMacPrivate::blockSendPostedEvents = false;
 
 #ifdef QT_MAC_USE_COCOA
 QStack<QCocoaModalSessionInfo> QEventDispatcherMacPrivate::cocoaModalSessionStack;
-bool QEventDispatcherMacPrivate::blockCocoaRequestModal = false;
+bool QEventDispatcherMacPrivate::currentExecIsNSAppRun = false;
+bool QEventDispatcherMacPrivate::nsAppRunCalledByQt = false;
+NSModalSession QEventDispatcherMacPrivate::currentModalSessionCached = 0;
 
-static void qt_mac_setChildDialogsResponsive(QWidget *widget, bool responsive)
+int QEventDispatcherMacPrivate::activeModalSessionCount()
 {
+    // Returns the number of modal sessions created
+    // (and not just pushed onto the stack, pending to be created)
+    int count = 0;
+    for (int i=cocoaModalSessionStack.size()-1; i>=0; --i) {
+        QCocoaModalSessionInfo &info = cocoaModalSessionStack[i];
+        if (info.session)
+            ++count;
+    }
+    return count;
+}
+
+void QEventDispatcherMacPrivate::temporarilyStopAllModalSessions()
+{
+    // Stop all created modal session, and as such, make then
+    // pending again. The next call to currentModalSession will
+    // recreate the session on top again:
+    int stackSize = cocoaModalSessionStack.size();
+    for (int i=stackSize-1; i>=0; --i) {
+        QCocoaModalSessionInfo &info = cocoaModalSessionStack[i];
+        if (info.session) {
+            [NSApp endModalSession:info.session];
+            info.session = 0;
+        }
+    }
+    currentModalSessionCached = 0;
+}
+
+NSModalSession QEventDispatcherMacPrivate::currentModalSession()
+{
+    // If we have one or more modal windows, this function will create
+    // a session for each of those, and return the one for the top.
+    if (currentModalSessionCached)
+        return currentModalSessionCached;
+
+    if (cocoaModalSessionStack.isEmpty())
+        return 0;
+
+    // Since this code will end up calling our Qt event handler
+    // (also from beginModalSessionForWindow), we need to block
+    // that to avoid side effects of events beeing delivered:
+    QBoolBlocker block(blockSendPostedEvents, true);
+
+    if (![NSApp isRunning]) {
+        // Sadly, we need to introduce this little event flush
+        // to stop dialogs from blinking/poping in front if a 
+        // modal session restart was needed:
+        while (NSEvent *event = [NSApp nextEventMatchingMask:NSAnyEventMask
+                untilDate:nil
+                inMode:NSDefaultRunLoopMode
+                dequeue: YES]) {
+            qt_mac_send_event(0, event, 0);
+        }
+    }
+
+    int sessionCount = cocoaModalSessionStack.size();
+    for (int i=0; i<sessionCount; ++i) {
+        QCocoaModalSessionInfo &info = cocoaModalSessionStack[i];
+        if (!info.widget)
+            continue;
+        if (info.widget->testAttribute(Qt::WA_DontShowOnScreen))
+            continue;
+        if (!info.session) {
+            QMacCocoaAutoReleasePool pool;
+            NSWindow *window = qt_mac_window_for(info.widget);
+            if (!window)
+                continue;
+            info.session = [NSApp beginModalSessionForWindow:window];
+        }
+        currentModalSessionCached = info.session;
+    }
+
+    return currentModalSessionCached;
+}
+
+static void setChildrenWorksWhenModal(QWidget *widget, bool worksWhenModal)
+{
+    // For NSPanels (but not NSWindows, sadly), we can set the flag
+    // worksWhenModal, so that they are active even when they are not modal. 
     QList<QDialog *> dialogs = widget->findChildren<QDialog *>();
     for (int i=0; i<dialogs.size(); ++i){
         NSWindow *window = qt_mac_window_for(dialogs[i]);
         if (window && [window isKindOfClass:[NSPanel class]]) {
-            [static_cast<NSPanel *>(window) setWorksWhenModal:responsive];
-            if (responsive && dialogs[i]->isVisible()){
+            [static_cast<NSPanel *>(window) setWorksWhenModal:worksWhenModal];
+            if (worksWhenModal && dialogs[i]->isVisible()){
                 [window orderFront:window];
             }
         }
     }
 }
 
-NSModalSession QEventDispatcherMacPrivate::activeModalSession()
+void QEventDispatcherMacPrivate::updateChildrenWorksWhenModal()
 {
-    // Create (if needed) and return the modal session
-    // for the  top-most modal dialog, if any:
-    if (cocoaModalSessionStack.isEmpty())
-        return 0;
-    QCocoaModalSessionInfo &info = cocoaModalSessionStack.last();
-    if (!info.widget)
-        return 0;
-    if (info.widget->testAttribute(Qt::WA_DontShowOnScreen)){
-        // INVARIANT: We have a modal widget, but it's not visible on screen.
-        // This will e.g. be true for native dialogs. Make the dialog children
-        // of the previous modal dialog unresponsive, so that the current dialog
-        // (native or not) is the only reponsive dialog on screen:
-        int size = cocoaModalSessionStack.size();
+    // Make the dialog children of the widget
+    // active. And make the dialog children of
+    // the previous modal dialog unactive again:
+    int size = cocoaModalSessionStack.size();
+    if (size > 0){
+        if (QWidget *prevModal = cocoaModalSessionStack[size-1].widget)
+            setChildrenWorksWhenModal(prevModal, true);
         if (size > 1){
             if (QWidget *prevModal = cocoaModalSessionStack[size-2].widget)
-                qt_mac_setChildDialogsResponsive(prevModal, false);
+                setChildrenWorksWhenModal(prevModal, false);
         }
-        return 0;
     }
+}
 
-    if (!info.session) {
-        QMacCocoaAutoReleasePool pool;
-        NSWindow *window = qt_mac_window_for(info.widget);
-        if (!window)
-            return 0;
-        // 'beginModalSessionForWindow' will give the event loop a spin, and as
-        // such, deliver Qt events. This might lead to inconsistent behaviour
-        // (especially if CocoaRequestModal is delivered), so we need to block:
-        QBoolBlocker block(blockSendPostedEvents, true);
-        info.session = [NSApp beginModalSessionForWindow:window];
-        // Make the dialog children of the current modal dialog
-        // responsive. And make the dialog children of
-        // the previous modal dialog unresponsive again:
-        qt_mac_setChildDialogsResponsive(info.widget, true);
-        int size = cocoaModalSessionStack.size();
-        if (size > 1){
-            if (QWidget *prevModal = cocoaModalSessionStack[size-2].widget)
-                qt_mac_setChildDialogsResponsive(prevModal, false);
-        }
-    }
-    return info.session;
+void QEventDispatcherMacPrivate::beginModalSession(QWidget *widget)
+{
+    // Add a new, empty (null), NSModalSession to the stack.
+    // It will become active the next time QEventDispatcher::processEvents is called.
+    // A QCocoaModalSessionInfo is considered pending to become active if the widget pointer 
+    // is non-zero, and the session pointer is zero (it will become active upon a call to
+    // currentModalSession). A QCocoaModalSessionInfo is considered pending to be stopped if
+    // the widget pointer is zero, and the session pointer is non-zero (it will be fully
+    // stopped in endModalSession().
+    QCocoaModalSessionInfo info = {widget, 0};
+    cocoaModalSessionStack.push(info);
+    updateChildrenWorksWhenModal();
+    currentModalSessionCached = 0;
 }
 
-void QEventDispatcherMacPrivate::rebuildModalSessionStack(bool pop)
+void QEventDispatcherMacPrivate::endModalSession(QWidget *widget)
 {
-    // Calling [NSApp stopModal], or [NSApp stop], will stop all modal dialogs
-    // in one go. So to to not confuse cocoa, we need to stop all our modal
-    // sessions as well. QMacEventDispatcher will make them modal again
-    // in the correct order as long as they are left on the cocoaModalSessionStack
-    // and a CocoaRequestModal is posted:
-    if (cocoaModalSessionStack.isEmpty())
-        return;
+    // Mark all sessions attached to widget as pending to be stopped. We do this
+    // by setting the widget pointer to zero, but leave the session pointer.
+    // We don't tell cocoa to stop any sessions just yet, because cocoa only understands
+    // when we stop the _current_ modal session (which is the session on top of
+    // the stack, and might not belong to 'widget'). 
+    int stackSize = cocoaModalSessionStack.size();
+    for (int i=stackSize-1; i>=0; --i) {
+        QCocoaModalSessionInfo &info = cocoaModalSessionStack[i];
+        if (info.widget == widget)
+            info.widget = 0;
+    }
 
-    QMacCocoaAutoReleasePool pool;
-    [NSApp stopModal];
-    [NSApp postEvent:[NSEvent otherEventWithType:NSApplicationDefined location:NSZeroPoint
-        modifierFlags:0 timestamp:0. windowNumber:0 context:0
-        subtype:SHRT_MAX data1:0 data2:0] atStart:NO];
+    // Now we stop, and remove, all sessions marked as pending
+    // to be stopped on _top_ of the stack, if any:
+    bool needToInterruptEventDispatcher = false;
+    bool needToUpdateChildrenWorksWhenModal = false;
 
-    for (int i=0; i<cocoaModalSessionStack.size(); ++i){
+    for (int i=stackSize-1; i>=0; --i) {
         QCocoaModalSessionInfo &info = cocoaModalSessionStack[i];
+        if (info.widget)
+            break;
+        cocoaModalSessionStack.remove(i);
+        needToUpdateChildrenWorksWhenModal = true;
+        currentModalSessionCached = 0;
         if (info.session) {
             [NSApp endModalSession:info.session];
-            info.session = 0;
+            needToInterruptEventDispatcher = true;
         }
     }
 
-    if (pop) {
-        QCocoaModalSessionInfo info = cocoaModalSessionStack.pop();
-        if (info.widget)
-            qt_mac_setChildDialogsResponsive(info.widget, false);
-    }
-
-    if (!cocoaModalSessionStack.isEmpty()) {
-        // Since we now have pending modal sessions again, make
-        // sure that we enter modal for the one on the top later:
-        qApp->postEvent(qApp, new QEvent(QEvent::CocoaRequestModal));
-    } else {
-        QCoreApplication::removePostedEvents(qApp, QEvent::CocoaRequestModal);
-    }
+    if (needToUpdateChildrenWorksWhenModal)
+        updateChildrenWorksWhenModal();
+    if (needToInterruptEventDispatcher)
+        QEventDispatcherMac::instance()->interrupt();
 }
 
 #endif
@@ -858,27 +938,29 @@ void QEventDispatcherMacPrivate::postedEventsSourcePerformCallback(void *info)
     }
 }
 
-#ifdef QT_MAC_USE_COCOA
-static void stopNSApp()
-{
-    QMacCocoaAutoReleasePool pool;
-    static const short NSAppShouldStopForQt = SHRT_MAX;
-    [NSApp stop:NSApp];
-    [NSApp postEvent:[NSEvent otherEventWithType:NSApplicationDefined location:NSZeroPoint
-                                   modifierFlags:0 timestamp:0. windowNumber:0 context:0
-                                         subtype:NSAppShouldStopForQt data1:0 data2:0] atStart:NO];
-}
-#endif
-
 void QEventDispatcherMac::interrupt()
 {
     Q_D(QEventDispatcherMac);
     d->interrupt = true;
     wakeUp();
+
 #ifndef QT_MAC_USE_COCOA
     CFRunLoopStop(mainRunLoop());
 #else
-    stopNSApp();
+    QMacCocoaAutoReleasePool pool;
+    // In case we wait for more events inside
+    // processEvents (or NSApp run), post a dummy to wake it up:
+    static const short NSAppShouldStopForQt = SHRT_MAX;
+    [NSApp postEvent:[NSEvent otherEventWithType:NSApplicationDefined location:NSZeroPoint
+        modifierFlags:0 timestamp:0. windowNumber:0 context:0
+        subtype:NSAppShouldStopForQt data1:0 data2:0] atStart:NO];
+
+    if (d->activeModalSessionCount() == 0) {
+        // We should only stop NSApp if we actually started it (and
+        // not some 3rd party application, e.g. if we are a plugin).
+        if (d->nsAppRunCalledByQt)
+            [NSApp stop:NSApp];
+    }
 #endif
 }
 
@@ -916,5 +998,52 @@ QEventDispatcherMac::~QEventDispatcherMac()
     CFRelease(d->waitingObserver);
 }
 
+/////////////////////////////////////////////////////////////////////////////
+
+#ifdef QT_MAC_USE_COCOA
+
+QtMacInterruptDispatcherHelp* QtMacInterruptDispatcherHelp::instance = 0;
+
+QtMacInterruptDispatcherHelp::QtMacInterruptDispatcherHelp() : cancelled(false)
+{
+    // This is the whole point of encapsulation this code
+    // inside a class; we can make the code (inside destructor)
+    // execute on lower loop level:
+    deleteLater();
+}
+
+QtMacInterruptDispatcherHelp::~QtMacInterruptDispatcherHelp()
+{
+    if (cancelled)
+        return;
+
+    instance = 0;
+
+    if (QEventDispatcherMacPrivate::currentExecIsNSAppRun) {
+        int activeCount = QEventDispatcherMacPrivate::activeModalSessionCount();
+        if (activeCount > 0) {
+            // The problem we now have hit: [NSApp stop] will not stop NSApp
+            // if a session is active; it will stop the session instead.
+            // So to stop NSApp, we need to temporarily stop all the
+            // sessions, then stop NSApp, then restart the session on top again.
+            // We need to do this to ensure that we're not stuck inside
+            // [NSApp run] when we really should be running a modal session:
+            QEventDispatcherMacPrivate::temporarilyStopAllModalSessions();
+        }
+    }
+    // Always interrupt once more in case the modal session stack changed
+    // while processEvents was called manually from within the application:
+    QEventDispatcherMac::instance()->interrupt();
+}
+
+void QtMacInterruptDispatcherHelp::interruptLater() {
+    if (instance) {
+        instance->cancelled = true;
+        delete instance;
+    }
+    instance = new QtMacInterruptDispatcherHelp;
+}
+
+#endif
 
 QT_END_NAMESPACE
diff --git a/src/gui/kernel/qeventdispatcher_mac_p.h b/src/gui/kernel/qeventdispatcher_mac_p.h
index 225d32e5c..6747d5231 100644
--- a/src/gui/kernel/qeventdispatcher_mac_p.h
+++ b/src/gui/kernel/qeventdispatcher_mac_p.h
@@ -172,9 +172,15 @@ public:
 #ifdef QT_MAC_USE_COCOA
     // The following variables help organizing modal sessions:
     static QStack<QCocoaModalSessionInfo> cocoaModalSessionStack;
-    static bool blockCocoaRequestModal;
-    static NSModalSession activeModalSession();
-    static void rebuildModalSessionStack(bool pop);
+    static bool currentExecIsNSAppRun;
+    static bool nsAppRunCalledByQt;
+    static NSModalSession currentModalSessionCached;
+    static void updateChildrenWorksWhenModal();
+    static NSModalSession currentModalSession();
+    static int activeModalSessionCount();
+    static void temporarilyStopAllModalSessions();
+    static void beginModalSession(QWidget *widget);
+    static void endModalSession(QWidget *widget);
 #endif
 
     MacSocketHash macSockets;
@@ -192,6 +198,20 @@ private:
                                         CFRunLoopActivity activity, void *info);
 };
 
+#ifdef QT_MAC_USE_COCOA
+class QtMacInterruptDispatcherHelp : public QObject
+{
+    static QtMacInterruptDispatcherHelp *instance;
+    bool cancelled;
+
+    QtMacInterruptDispatcherHelp();
+    ~QtMacInterruptDispatcherHelp();
+
+    public:
+    static void interruptLater();
+};
+#endif
+
 QT_END_NAMESPACE
 
 #endif // QEVENTDISPATCHER_MAC_P_H
diff --git a/src/gui/kernel/qwidget_mac.mm b/src/gui/kernel/qwidget_mac.mm
index 48a4bc334..5948cd4c7 100644
--- a/src/gui/kernel/qwidget_mac.mm
+++ b/src/gui/kernel/qwidget_mac.mm
@@ -3197,10 +3197,13 @@ void QWidgetPrivate::show_sys()
 #else
             // sync the opacity value back (in case of a fade).
             [window setAlphaValue:q->windowOpacity()];
-
             [window makeKeyAndOrderFront:window];
+
+            // If this window is app modal, we need to start spinning
+            // a modal session for it. Interrupting
+            // the event dispatcher will make this happend:
             if (data.window_modality == Qt::ApplicationModal)
-                QCoreApplication::postEvent(qApp, new QEvent(QEvent::CocoaRequestModal));
+                QEventDispatcherMac::instance()->interrupt();
 #endif
             if (q->windowType() == Qt::Popup) {
 			    if (q->focusWidget())
@@ -3218,13 +3221,6 @@ void QWidgetPrivate::show_sys()
 #endif
         } else if (!q->testAttribute(Qt::WA_ShowWithoutActivating)) {
             qt_event_request_activate(q);
-#ifdef QT_MAC_USE_COCOA
-            if (q->windowModality() == Qt::ApplicationModal) {
-                // We call 'activeModalSession' early to force creation of q's modal
-                // session. This seems neccessary for child dialogs to pop to front:
-                QEventDispatcherMacPrivate::activeModalSession();
-            }
-#endif
         }
     } else if(topData()->embedded || !q->parentWidget() || q->parentWidget()->isVisible()) {
 #ifndef QT_MAC_USE_COCOA