QThread: fix race when setting the eventDispatcher

Use QMutexLocker to make this thread-safe.

Task-number: QTBUG-29452
(cherry picked and adapted from qtbase/f4609b202208fe592d24c7ae3b4a48ee83045497)
Change-Id: I5caf71d9a5dc6e3d655eac84426a0c5592772235
Reviewed-by: Louai Al-Khanji <[email protected]>

Author: Andy Shaw

src/corelib/thread/qthread_symbian.cpp

@@ -336,7 +336,9 @@ typedef void*(*QtThreadCallback)(void*);
 
 void QThreadPrivate::createEventDispatcher(QThreadData *data)
 {
+    QMutexLocker l(&data->postEventList.mutex);
     data->eventDispatcher = new QEventDispatcherSymbian;
+    l.unlock();
     data->eventDispatcher->startingUp();
 }
 

src/corelib/thread/qthread_unix.cpp

@@ -273,6 +273,8 @@ typedef void*(*QtThreadCallback)(void*);
 
 void QThreadPrivate::createEventDispatcher(QThreadData *data)
 {
+    QMutexLocker l(&data->postEventList.mutex);
+
 #if defined(Q_OS_BLACKBERRY)
     data->eventDispatcher = new QEventDispatcherBlackberry;
 #else
@@ -286,6 +288,7 @@ void QThreadPrivate::createEventDispatcher(QThreadData *data)
     data->eventDispatcher = new QEventDispatcherUNIX;
 #endif
 
+    l.unlock();
     data->eventDispatcher->startingUp();
 }
 

src/corelib/thread/qthread_win.cpp

@@ -318,7 +318,9 @@ void qt_set_thread_name(HANDLE threadId, LPCSTR threadName)
 
 void QThreadPrivate::createEventDispatcher(QThreadData *data)
 {
+    QMutexLocker l(&data->postEventList.mutex);
     data->eventDispatcher = new QEventDispatcherWin32;
+    l.unlock();
     data->eventDispatcher->startingUp();
 }