Allow to create a custom event dispatcher for specific QThreads.

QAbstractEventDispatcher() does no longer install itself into the current
thread.  Instead the new methods QThread::setEventDispatcher() and
QCoreApplication::setEventDispatcher() allow to install a custom event
dispatcher into any QThread as long as there is no default event dispatcher
created yet.  That is, before the thread has been started with
QThread::start() or, in case of the main thread, before QCoreApplication has
been instantiated.

Change-Id: I7367e13d8d8aebed5a5651260bb69b8818eb1b90
Reviewed-by: Olivier Goffart <ogoffart@woboq.com>
Reviewed-by: Bradley T. Hughes <bradley.hughes@nokia.com>

4 files changed, 37 insertions, 25 deletions

diff --git a/src/corelib/kernel/qabstracteventdispatcher.cpp b/src/corelib/kernel/qabstracteventdispatcher.cpp
index 10de2caf62..b936ac4ed2 100644
--- a/src/corelib/kernel/qabstracteventdispatcher.cpp
+++ b/src/corelib/kernel/qabstracteventdispatcher.cpp
@@ -49,16 +49,6 @@
 
 QT_BEGIN_NAMESPACE
 
-void QAbstractEventDispatcherPrivate::init()
-{
-    Q_Q(QAbstractEventDispatcher);
-    if (threadData->eventDispatcher != 0) {
-        qWarning("QAbstractEventDispatcher: An event dispatcher has already been created for this thread");
-    } else {
-        threadData->eventDispatcher = q;
-    }
-}
-
 // we allow for 2^24 = 8^8 = 16777216 simultaneously running timers
 struct QtTimerIdFreeListConstants : public QFreeListDefaultConstants
 {
@@ -127,8 +117,9 @@ void QAbstractEventDispatcherPrivate::releaseTimerId(int timerId)
     instance() and call functions on the QAbstractEventDispatcher
     object that is returned. If you want to use your own instance of
     QAbstractEventDispatcher or of a QAbstractEventDispatcher
-    subclass, you must create your instance \e before you create the
-    QApplication object.
+    subclass, you must install it with QCoreApplication::setEventDispatcher()
+    or QThread::setEventDispatcher() \e before a default event dispatcher has
+    been installed.
 
     The main event loop is started by calling
     QCoreApplication::exec(), and stopped by calling
@@ -145,29 +136,21 @@ void QAbstractEventDispatcherPrivate::releaseTimerId(int timerId)
     reimplementation of QAbstractEventDispatcher that merges Qt and
     Motif events together.
 
-    \sa QEventLoop, QCoreApplication
+    \sa QEventLoop, QCoreApplication, QThread
 */
 
 /*!
     Constructs a new event dispatcher with the given \a parent.
 */
 QAbstractEventDispatcher::QAbstractEventDispatcher(QObject *parent)
-    : QObject(*new QAbstractEventDispatcherPrivate, parent)
-{
-    Q_D(QAbstractEventDispatcher);
-    d->init();
-}
+    : QObject(*new QAbstractEventDispatcherPrivate, parent) {}
 
 /*!
     \internal
 */
 QAbstractEventDispatcher::QAbstractEventDispatcher(QAbstractEventDispatcherPrivate &dd,
                                                    QObject *parent)
-    : QObject(dd, parent)
-{
-    Q_D(QAbstractEventDispatcher);
-    d->init();
-}
+    : QObject(dd, parent) {}
 
 /*!
     Destroys the event dispatcher.
diff --git a/src/corelib/kernel/qabstracteventdispatcher_p.h b/src/corelib/kernel/qabstracteventdispatcher_p.h
index 620a4499e2..31c579d865 100644
--- a/src/corelib/kernel/qabstracteventdispatcher_p.h
+++ b/src/corelib/kernel/qabstracteventdispatcher_p.h
@@ -67,7 +67,6 @@ public:
     inline QAbstractEventDispatcherPrivate()
         : event_filter(0)
     { }
-    void init();
     QAbstractEventDispatcher::EventFilter event_filter;
 
     static int allocateTimerId();
diff --git a/src/corelib/kernel/qcoreapplication.cpp b/src/corelib/kernel/qcoreapplication.cpp
index 9408d414f0..c30f6135a9 100644
--- a/src/corelib/kernel/qcoreapplication.cpp
+++ b/src/corelib/kernel/qcoreapplication.cpp
@@ -660,8 +660,10 @@ void QCoreApplication::init()
         d->createEventDispatcher();
     Q_ASSERT(QCoreApplicationPrivate::eventDispatcher != 0);
 
-    if (!QCoreApplicationPrivate::eventDispatcher->parent())
+    if (!QCoreApplicationPrivate::eventDispatcher->parent()) {
         QCoreApplicationPrivate::eventDispatcher->moveToThread(d->threadData->thread);
+        QCoreApplicationPrivate::eventDispatcher->setParent(this);
+    }
 
     d->threadData->eventDispatcher = QCoreApplicationPrivate::eventDispatcher;
 
@@ -2517,6 +2519,31 @@ bool QCoreApplication::hasPendingEvents()
     return false;
 }
 
+/*!
+    Returns a pointer to the event dispatcher object for the main thread. If no
+    event dispatcher exists for the thread, this function returns 0.
+*/
+QAbstractEventDispatcher *QCoreApplication::eventDispatcher()
+{
+    if (QCoreApplicationPrivate::theMainThread)
+        return QCoreApplicationPrivate::theMainThread->eventDispatcher();
+    return 0;
+}
+
+/*!
+    Sets the event dispatcher for the main thread to \a eventDispatcher. This
+    is only possible as long as there is no event dispatcher installed yet. That
+    is, before QCoreApplication has been instantiated. This method takes
+    ownership of the object.
+*/
+void QCoreApplication::setEventDispatcher(QAbstractEventDispatcher *eventDispatcher)
+{
+    QThread *mainThread = QCoreApplicationPrivate::theMainThread;
+    if (!mainThread)
+        mainThread = QThread::currentThread(); // will also setup theMainThread
+    mainThread->setEventDispatcher(eventDispatcher);
+}
+
 /*
     \fn void QCoreApplication::watchUnixSignal(int signal, bool watch)
     \internal
diff --git a/src/corelib/kernel/qcoreapplication.h b/src/corelib/kernel/qcoreapplication.h
index ce3f349844..4d3ee9bc7a 100644
--- a/src/corelib/kernel/qcoreapplication.h
+++ b/src/corelib/kernel/qcoreapplication.h
@@ -61,6 +61,7 @@ class QTextCodec;
 class QTranslator;
 class QPostEventList;
 class QStringList;
+class QAbstractEventDispatcher;
 
 #define qApp QCoreApplication::instance()
 
@@ -114,6 +115,8 @@ public:
     static void removePostedEvents(QObject *receiver);
     static void removePostedEvents(QObject *receiver, int eventType);
     static bool hasPendingEvents();
+    static QAbstractEventDispatcher *eventDispatcher();
+    static void setEventDispatcher(QAbstractEventDispatcher *eventDispatcher);
 
     virtual bool notify(QObject *, QEvent *);