Fix dead lock in the Qt event handling

The deadlock is caused because the QEvent is destroyed while holding the
event list mutex. And the QEvent may have a custom destructor that will
re-enter the event handlng code.

The QScopedPointer that should destroy the event must be created after
the MutexUnlocker.

Regression introduced by commit f9035587b98ac5dc9491e642b8ec84470ec03f0e

Task-number: QTBUG-31606
Change-Id: I6b2cbc2656eacdec61b641886953f00bf5b3ff36
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

1 files changed, 4 insertions, 2 deletions

diff --git a/src/corelib/kernel/qcoreapplication.cpp b/src/corelib/kernel/qcoreapplication.cpp
index 0301a40876..c3a05551b8 100644
--- a/src/corelib/kernel/qcoreapplication.cpp
+++ b/src/corelib/kernel/qcoreapplication.cpp
@@ -1451,7 +1451,7 @@ void QCoreApplicationPrivate::sendPostedEvents(QObject *receiver, int event_type
         // first, we diddle the event so that we can deliver
         // it, and that no one will try to touch it later.
         pe.event->posted = false;
-        QScopedPointer<QEvent> e(pe.event);
+        QEvent *e = pe.event;
         QObject * r = pe.receiver;
 
         --r->d_func()->postedEvents;
@@ -1469,8 +1469,10 @@ void QCoreApplicationPrivate::sendPostedEvents(QObject *receiver, int event_type
         };
         MutexUnlocker unlocker(locker);
 
+        QScopedPointer<QEvent> event_deleter(e); // will delete the event (with the mutex unlocked)
+
         // after all that work, it's time to deliver the event.
-        QCoreApplication::sendEvent(r, e.data());
+        QCoreApplication::sendEvent(r, e);
 
         // careful when adding anything below this point - the
         // sendEvent() call might invalidate any invariants this