Fix crash in flushWindowSystemEvents() in QGuiApplication-cleanup.

Check for existence of QGuiApplication, discard events if it is 0.

Change-Id: I04b27679033fb13ef2fa38e39757d89465cba94b
Reviewed-by: Shawn Rutledge <shawn.rutledge@digia.com>
Reviewed-by: Samuel Rødal <samuel.rodal@digia.com>

2 files changed, 13 insertions, 2 deletions

diff --git a/src/gui/kernel/qwindowsysteminterface.cpp b/src/gui/kernel/qwindowsysteminterface.cpp
index 8c5a3bc215..3609d5dce6 100644
--- a/src/gui/kernel/qwindowsysteminterface.cpp
+++ b/src/gui/kernel/qwindowsysteminterface.cpp
@@ -527,6 +527,16 @@ void QWindowSystemInterface::deferredFlushWindowSystemEvents()
 
 void QWindowSystemInterface::flushWindowSystemEvents()
 {
+    const int count = QWindowSystemInterfacePrivate::windowSystemEventQueue.count();
+    if (!count)
+        return;
+    if (!QGuiApplication::instance()) {
+        qWarning().nospace()
+            << "QWindowSystemInterface::flushWindowSystemEvents() invoked after "
+               "QGuiApplication destruction, discarding " << count << " events.";
+        QWindowSystemInterfacePrivate::windowSystemEventQueue.clear();
+        return;
+    }
     if (QThread::currentThread() != QGuiApplication::instance()->thread()) {
         QMutexLocker locker(&QWindowSystemInterfacePrivate::flushEventMutex);
         QWindowSystemInterfacePrivate::FlushEventsEvent *e = new QWindowSystemInterfacePrivate::FlushEventsEvent();
diff --git a/src/gui/kernel/qwindowsysteminterface_p.h b/src/gui/kernel/qwindowsysteminterface_p.h
index 431b2cbe1e..eca559abfa 100644
--- a/src/gui/kernel/qwindowsysteminterface_p.h
+++ b/src/gui/kernel/qwindowsysteminterface_p.h
@@ -387,9 +387,10 @@ public:
         mutable QMutex mutex;
     public:
         WindowSystemEventList() : impl(), mutex() {}
-        ~WindowSystemEventList()
-        { const QMutexLocker locker(&mutex); qDeleteAll(impl); impl.clear(); }
+        ~WindowSystemEventList() { clear(); }
 
+        void clear()
+        { const QMutexLocker locker(&mutex); qDeleteAll(impl); impl.clear(); }
         void prepend(WindowSystemEvent *e)
         { const QMutexLocker locker(&mutex); impl.prepend(e); }
         WindowSystemEvent *takeFirstOrReturnNull()