Add QDeferredDeleteEvent

Use this to store the loop-level counter needed by QCoreApplication
when determining when it is safe to delete an object.

This removes the hack to hijack the QEvent::d pointer (even though
the pointer is unused).

Change-Id: I91c0b1aa00235ec6e13feb30bf928e56d2f80026
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/corelib/kernel/qcoreapplication.cpp

@@ -1105,13 +1105,7 @@ void QCoreApplication::postEvent(QObject *receiver, QEvent *event, int priority)
     if (event->type() == QEvent::DeferredDelete && data == QThreadData::current()) {
         // remember the current running eventloop for DeferredDelete
         // events posted in the receiver's thread
-
-        // check that QEvent's d pointer is unused before we store the loop level
-        // if further updates to QEvent have made the use of the d pointer necessary,
-        // then update this code to store the loop level somewhere else
-        Q_ASSERT_X(event->d == 0, "QCoreApplication::postEvent",
-                   "Internal error: this code relies on QEvent::d being null");
-        event->d = reinterpret_cast<QEventPrivate *>(quintptr(data->loopLevel));
+        static_cast<QDeferredDeleteEvent *>(event)->level = data->loopLevel;
     }
 
     // delete the event on exceptions to protect against memory leaks till the event is
@@ -1280,11 +1274,12 @@ void QCoreApplicationPrivate::sendPostedEvents(QObject *receiver, int event_type
             // DeferredDelete events are only sent when we are explicitly asked to
             // (s.a. QEvent::DeferredDelete), and then only if the event loop that
             // posted the event has returned.
+            int loopLevel = static_cast<QDeferredDeleteEvent *>(pe.event)->loopLevel();
             const bool allowDeferredDelete =
-                (quintptr(pe.event->d) > unsigned(data->loopLevel)
-                 || (!quintptr(pe.event->d) && data->loopLevel > 0)
+                (loopLevel > data->loopLevel
+                 || (!loopLevel && data->loopLevel > 0)
                  || (event_type == QEvent::DeferredDelete
-                     && quintptr(pe.event->d) == unsigned(data->loopLevel)));
+                     && loopLevel == data->loopLevel));
             if (!allowDeferredDelete) {
                 // cannot send deferred delete
                 if (!event_type && !receiver) {

src/corelib/kernel/qcoreevent.cpp

@@ -116,7 +116,7 @@ QT_BEGIN_NAMESPACE
     \value ContentsRectChange               The margins of the widget's content rect changed.
     \value ContextMenu                      Context popup menu (QContextMenuEvent).
     \value CursorChange                     The widget's cursor has changed.
-    \value DeferredDelete                   The object will be deleted after it has cleaned up.
+    \value DeferredDelete                   The object will be deleted after it has cleaned up (QDeferredDeleteEvent).
     \value DragEnter                        The cursor enters a widget during a drag and drop operation (QDragEnterEvent).
     \value DragLeave                        The cursor leaves a widget during a drag and drop operation (QDragLeaveEvent).
     \value DragMove                         A drag and drop operation is in progress (QDragMoveEvent).
@@ -580,4 +580,24 @@ QDynamicPropertyChangeEvent::~QDynamicPropertyChangeEvent()
     \sa QObject::setProperty(), QObject::dynamicPropertyNames()
 */
 
+/*!
+    Constructs a deferred delete event with an initial loopLevel() of zero.
+*/
+QDeferredDeleteEvent::QDeferredDeleteEvent()
+    : QEvent(QEvent::DeferredDelete)
+    , level(0)
+{ }
+
+/*! \internal */
+QDeferredDeleteEvent::~QDeferredDeleteEvent()
+{ }
+
+/*! \fn int QDeferredDeleteEvent::loopLevel() const
+
+    Returns the loop-level in which the event was posted. The
+    loop-level is set by QCoreApplication::postEvent().
+
+    \sa QObject::deleteLater()
+*/
+
 QT_END_NAMESPACE

src/corelib/kernel/qcoreevent.h

@@ -360,6 +360,17 @@ private:
     QByteArray n;
 };
 
+class Q_CORE_EXPORT QDeferredDeleteEvent : public QEvent
+{
+public:
+    explicit QDeferredDeleteEvent();
+    ~QDeferredDeleteEvent();
+    int loopLevel() const { return level; }
+private:
+    int level;
+    friend class QCoreApplication;
+};
+
 QT_END_NAMESPACE
 
 QT_END_HEADER

src/corelib/kernel/qobject.cpp

@@ -1907,7 +1907,7 @@ void QObject::removeEventFilter(QObject *obj)
 */
 void QObject::deleteLater()
 {
-    QCoreApplication::postEvent(this, new QEvent(QEvent::DeferredDelete));
+    QCoreApplication::postEvent(this, new QDeferredDeleteEvent());
 }
 
 /*!

tests/auto/widgets/kernel/qapplication/tst_qapplication.cpp

@@ -1045,7 +1045,7 @@ void SendPostedEventsTester::doTest()
     QPointer<SendPostedEventsTester> p = this;
     QApplication::postEvent(this, new QEvent(QEvent::User));
     // DeferredDelete should not be delivered until returning from this function
-    QApplication::postEvent(this, new QEvent(QEvent::DeferredDelete));
+    QApplication::postEvent(this, new QDeferredDeleteEvent());
 
     QEventLoop eventLoop;
     QMetaObject::invokeMethod(&eventLoop, "quit", Qt::QueuedConnection);