xcb: Don't connect() to event-dispatcher until we are sure we have one

QCoreApplication sets up the event dispatcher in the constructor, through
createEventDispatcher(), which is overridden in QGuiApplication to take
the platform-integration into account. The problem is that the platform
integration is created before the event dispatcher, so when we create the
QXcbConnection we are not guaranteed to have an event dispatcher yet.

This is not an issue when using xcb_poll_for_queued_event() in a thread,
but for the fallback case we connect to the event-dispatcher's awake()
and aboutToBlock() signals. To ensure that we do this only when we have
an event dispatcher we post a queued method invocation, that will be
processed as one of the first events once there is an event-dispatcher.

Change-Id: I623011af447b585884b84c7559737f134aab83e8
Reviewed-by: Jędrzej Nowacki <jedrzej.nowacki@digia.com>
Reviewed-by: Uli Schlachter <psychon@znc.in>
Reviewed-by: Shawn Rutledge <shawn.rutledge@digia.com>

1 files changed, 6 insertions, 1 deletions

diff --git a/src/plugins/platforms/xcb/qxcbconnection.h b/src/plugins/platforms/xcb/qxcbconnection.h
index 7cabe67a68..0e52b2ec46 100644
--- a/src/plugins/platforms/xcb/qxcbconnection.h
+++ b/src/plugins/platforms/xcb/qxcbconnection.h
@@ -298,11 +298,14 @@ public:
     QXcbEventArray *lock();
     void unlock();
 
-    bool startThread();
+    void start();
 
 signals:
     void eventPending();
 
+private slots:
+    void registerForEvents();
+
 private:
     void addEvent(xcb_generic_event_t *event);
 
@@ -574,6 +577,8 @@ private:
 
     QByteArray m_startupId;
     QXcbSystemTrayTracker *m_systemTrayTracker;
+
+    friend class QXcbEventReader;
 };
 
 #define DISPLAY_FROM_XCB(object) ((Display *)(object->connection()->xlib_display()))