statemachine: Make delayed event posting work from secondary thread

postDelayedEvent() and cancelDelayedEvent() are marked as thread-safe
in the documentation. Unfortunately, they didn't actually work when
called from another thread; they just produced some warnings:

QObject::startTimer: timers cannot be started from another thread
QObject::killTimer: timers cannot be stopped from another thread

As the warnings indicate, the issue was that postDelayedEvent()
(cancelDelayedEvent()) unconditionally called QObject::startTimer()
(stopTimer()), i.e. without considering which thread the function
was called from.

If the function is called from a different thread, the actual
starting/stopping of the associated timer is now done from the
correct thread, by asynchronously calling a private slot on the
state machine.

This also means that the raw timer id can no longer be used as the
id of the delayed event, since a valid event id must be returned
before the timer has started. The state machine now manages those
ids itself (using a QFreeList, just like startTimer() and
killTimer() do), and also keeps a mapping from timer id to event
id once the timer has been started. This is inherently more complex
than before, but at least the API should work as advertised/intended
now.

Task-number: QTBUG-17975
Change-Id: I3a866d01dca23174c8841112af50b87141df0943
Reviewed-by: Eskil Abrahamsen Blomfeldt <eskil.abrahamsen-blomfeldt@nokia.com>

1 files changed, 14 insertions, 1 deletions

diff --git a/src/corelib/statemachine/qstatemachine_p.h b/src/corelib/statemachine/qstatemachine_p.h
index d01b050e15..ae5660719f 100644
--- a/src/corelib/statemachine/qstatemachine_p.h
+++ b/src/corelib/statemachine/qstatemachine_p.h
@@ -62,6 +62,7 @@
 #include <QtCore/qpair.h>
 #include <QtCore/qset.h>
 #include <QtCore/qvector.h>
+#include <private/qfreelist_p.h>
 
 QT_BEGIN_NAMESPACE
 
@@ -120,6 +121,8 @@ public:
 #ifndef QT_NO_ANIMATION
     void _q_animationFinished();
 #endif
+    void _q_startDelayedEventTimer(int id, int delay);
+    void _q_killDelayedEventTimer(int id, int timerId);
 
     QState *rootState() const;
 
@@ -232,7 +235,17 @@ public:
 #ifndef QT_NO_STATEMACHINE_EVENTFILTER
     QHash<QObject*, QHash<QEvent::Type, int> > qobjectEvents;
 #endif
-    QHash<int, QEvent*> delayedEvents;
+    QFreeList<void> delayedEventIdFreeList;
+    struct DelayedEvent {
+        QEvent *event;
+        int timerId;
+        DelayedEvent(QEvent *e, int tid)
+            : event(e), timerId(tid) {}
+        DelayedEvent()
+            : event(0), timerId(0) {}
+    };
+    QHash<int, DelayedEvent> delayedEvents;
+    QHash<int, int> timerIdToDelayedEventId;
     QMutex delayedEventsMutex;
   
     typedef QEvent* (*f_cloneEvent)(QEvent*);