Make flushWindowSystemEvents return ev. accepted

flushWindowSystemEvents() now returns whether the
most recent event added to the queue was accepted
by Qt or not.

Use QAtomicInt to store the accepted state in order
to avoid a data race on it between the Gui thread
and the event poster thread.

Change-Id: I6c111fdaecda5c514307ca0749a54075fe8e872f
Reviewed-by: Jørgen Lind <jorgen.lind@theqtcompany.com>

3 files changed, 19 insertions, 4 deletions

diff --git a/src/gui/kernel/qwindowsysteminterface.cpp b/src/gui/kernel/qwindowsysteminterface.cpp
index 88cf2dac93..01f4be6dd0 100644
--- a/src/gui/kernel/qwindowsysteminterface.cpp
+++ b/src/gui/kernel/qwindowsysteminterface.cpp
@@ -49,6 +49,7 @@ QElapsedTimer QWindowSystemInterfacePrivate::eventTime;
 bool QWindowSystemInterfacePrivate::synchronousWindowSystemEvents = false;
 QWaitCondition QWindowSystemInterfacePrivate::eventsFlushed;
 QMutex QWindowSystemInterfacePrivate::flushEventMutex;
+QAtomicInt QWindowSystemInterfacePrivate::eventAccepted;
 QWindowSystemEventHandler *QWindowSystemInterfacePrivate::eventHandler;
 
 //------------------------------------------------------------
@@ -618,17 +619,21 @@ void QWindowSystemInterface::deferredFlushWindowSystemEvents(QEventLoop::Process
     QWindowSystemInterfacePrivate::eventsFlushed.wakeOne();
 }
 
-void QWindowSystemInterface::flushWindowSystemEvents(QEventLoop::ProcessEventsFlags flags)
+/*!
+    Make Qt Gui process all events on the event queue immediately. Return the
+    accepted state for the last event on the queue.
+*/
+bool QWindowSystemInterface::flushWindowSystemEvents(QEventLoop::ProcessEventsFlags flags)
 {
     const int count = QWindowSystemInterfacePrivate::windowSystemEventQueue.count();
     if (!count)
-        return;
+        return false;
     if (!QGuiApplication::instance()) {
         qWarning().nospace()
             << "QWindowSystemInterface::flushWindowSystemEvents() invoked after "
                "QGuiApplication destruction, discarding " << count << " events.";
         QWindowSystemInterfacePrivate::windowSystemEventQueue.clear();
-        return;
+        return false;
     }
     if (QThread::currentThread() != QGuiApplication::instance()->thread()) {
         QMutexLocker locker(&QWindowSystemInterfacePrivate::flushEventMutex);
@@ -638,6 +643,7 @@ void QWindowSystemInterface::flushWindowSystemEvents(QEventLoop::ProcessEventsFl
     } else {
         sendWindowSystemEvents(flags);
     }
+    return QWindowSystemInterfacePrivate::eventAccepted.load() > 0;
 }
 
 bool QWindowSystemInterface::sendWindowSystemEvents(QEventLoop::ProcessEventsFlags flags)
@@ -659,6 +665,13 @@ bool QWindowSystemInterface::sendWindowSystemEvents(QEventLoop::ProcessEventsFla
             nevents++;
             QGuiApplicationPrivate::processWindowSystemEvent(event);
         }
+
+        // Record the accepted state for the processed event
+        // (excluding flush events). This state can then be
+        // returned by flushWindowSystemEvents().
+        if (event->type != QWindowSystemInterfacePrivate::FlushEvents)
+            QWindowSystemInterfacePrivate::eventAccepted.store(event->eventAccepted);
+
         delete event;
     }
 
diff --git a/src/gui/kernel/qwindowsysteminterface.h b/src/gui/kernel/qwindowsysteminterface.h
index ace1a4fe24..3e0b788c0f 100644
--- a/src/gui/kernel/qwindowsysteminterface.h
+++ b/src/gui/kernel/qwindowsysteminterface.h
@@ -213,7 +213,7 @@ public:
     // For event dispatcher implementations
     static bool sendWindowSystemEvents(QEventLoop::ProcessEventsFlags flags);
     static void setSynchronousWindowSystemEvents(bool enable);
-    static void flushWindowSystemEvents(QEventLoop::ProcessEventsFlags flags = QEventLoop::AllEvents);
+    static bool flushWindowSystemEvents(QEventLoop::ProcessEventsFlags flags = QEventLoop::AllEvents);
     static void deferredFlushWindowSystemEvents(QEventLoop::ProcessEventsFlags flags);
     static int windowSystemEventsQueued();
 };
diff --git a/src/gui/kernel/qwindowsysteminterface_p.h b/src/gui/kernel/qwindowsysteminterface_p.h
index cc0ca6bf81..430800f137 100644
--- a/src/gui/kernel/qwindowsysteminterface_p.h
+++ b/src/gui/kernel/qwindowsysteminterface_p.h
@@ -51,6 +51,7 @@
 #include <QMutex>
 #include <QList>
 #include <QWaitCondition>
+#include <QAtomicInt>
 
 QT_BEGIN_NAMESPACE
 
@@ -488,6 +489,7 @@ public:
 
     static QWaitCondition eventsFlushed;
     static QMutex flushEventMutex;
+    static QAtomicInt eventAccepted;
 
     static QList<QTouchEvent::TouchPoint>
         fromNativeTouchPoints(const QList<QWindowSystemInterface::TouchPoint> &points,