QThread: Centralize the creation of the event dispatcher

In some places we call startingUp(), in others we don't. It's probably
ok for those that have just created an object of a given class, which
knows whether the virtual call is necessary or not. But for the generic
case, we do call it.

Change-Id: If48c5c2e920c433298f1fffd153ee1cc75703204
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@qt.io>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/corelib/kernel/qcoreapplication.cpp

@@ -540,7 +540,7 @@ void QCoreApplicationPrivate::createEventDispatcher()
     Q_Q(QCoreApplication);
     QThreadData *data = QThreadData::current();
     Q_ASSERT(!data->hasEventDispatcher());
-    eventDispatcher = QThreadPrivate::createEventDispatcher(data);
+    eventDispatcher = data->createEventDispatcher();
     eventDispatcher->setParent(q);
 }
 

src/corelib/kernel/qeventloop.cpp

@@ -101,10 +101,8 @@ QEventLoop::QEventLoop(QObject *parent)
     Q_D(QEventLoop);
     if (!QCoreApplication::instance() && QCoreApplicationPrivate::threadRequiresCoreApplication()) {
         qWarning("QEventLoop: Cannot be used without QApplication");
-    } else if (!d->threadData->hasEventDispatcher()) {
-        QAbstractEventDispatcher *eventDispatcher = QThreadPrivate::createEventDispatcher(d->threadData);
-        d->threadData->eventDispatcher.storeRelease(eventDispatcher);
-        eventDispatcher->startingUp();
+    } else {
+        d->threadData->ensureEventDispatcher();
     }
 }
 

src/corelib/thread/qthread.cpp

@@ -117,6 +117,14 @@ void QThreadData::deref()
 #endif
 }
 
+QAbstractEventDispatcher *QThreadData::createEventDispatcher()
+{
+    QAbstractEventDispatcher *ed = QThreadPrivate::createEventDispatcher(this);
+    eventDispatcher.storeRelease(ed);
+    ed->startingUp();
+    return ed;
+}
+
 /*
   QAdoptedThread
 */

src/corelib/thread/qthread_p.h

@@ -248,7 +248,15 @@ public:
     void ref();
     void deref();
     inline bool hasEventDispatcher() const
-    { return eventDispatcher.load() != 0; }
+    { return eventDispatcher.load() != nullptr; }
+    QAbstractEventDispatcher *createEventDispatcher();
+    QAbstractEventDispatcher *ensureEventDispatcher()
+    {
+        QAbstractEventDispatcher *ed = eventDispatcher.load();
+        if (Q_LIKELY(ed))
+            return ed;
+        return createEventDispatcher();
+    }
 
     bool canWaitLocked()
     {

src/corelib/thread/qthread_unix.cpp

@@ -339,13 +339,7 @@ void *QThreadPrivate::start(void *arg)
             data->quitNow = thr->d_func()->exited;
         }
 
-        QAbstractEventDispatcher *eventDispatcher = data->eventDispatcher.load();
-        if (!eventDispatcher) {
-            eventDispatcher = createEventDispatcher(data);
-            data->eventDispatcher.storeRelease(eventDispatcher);
-        }
-
-        eventDispatcher->startingUp();
+        data->ensureEventDispatcher();
 
 #if (defined(Q_OS_LINUX) || defined(Q_OS_MAC) || defined(Q_OS_QNX))
         {

src/corelib/thread/qthread_win.cpp

@@ -360,13 +360,7 @@ unsigned int __stdcall QT_ENSURE_STACK_ALIGNED_FOR_SSE QThreadPrivate::start(voi
         data->quitNow = thr->d_func()->exited;
     }
 
-    QAbstractEventDispatcher *eventDispatcher = data->eventDispatcher.load();
-    if (!eventDispatcher) {
-        eventDispatcher = createEventDispatcher(data);
-        data->eventDispatcher.storeRelease(eventDispatcher);
-    }
-
-    eventDispatcher->startingUp();
+    data->ensureEventDispatcher();
 
 #if !defined(QT_NO_DEBUG) && defined(Q_CC_MSVC) && !defined(Q_OS_WINRT)
     // sets the name of the current thread.