QTimerInfoList: refactor unregisterTimers()

- Use removeIf(), easier to reason about than removing from the list
  during iteration
- Return true only if any timers were actually unregistered
- Assert in QObject::event() that if the list returned by
  eventDispatcher->registeredTimers() isn't empty, then
  eventDispatcher->unregisteredTimers() returns true

Change-Id: I739a3865b7524a7aab3ff0227e6a060ed98d6191
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/corelib/kernel/qobject.cpp

@@ -1415,8 +1415,11 @@ bool QObject::event(QEvent *e)
         if (eventDispatcher) {
             QList<QAbstractEventDispatcher::TimerInfo> timers = eventDispatcher->registeredTimers(this);
             if (!timers.isEmpty()) {
+                const bool res = eventDispatcher->unregisterTimers(this);
                 // do not to release our timer ids back to the pool (since the timer ids are moving to a new thread).
-                eventDispatcher->unregisterTimers(this);
+                Q_ASSERT_X(res, Q_FUNC_INFO,
+                           "QAbstractEventDispatcher::unregisterTimers() returned false,"
+                           " but there are timers associated with this object.");
                 QMetaObject::invokeMethod(this, "_q_reregisterTimers", Qt::QueuedConnection,
                                           Q_ARG(void*, (new QList<QAbstractEventDispatcher::TimerInfo>(timers))));
             }

src/corelib/kernel/qtimerinfo_unix.cpp

@@ -353,22 +353,24 @@ bool QTimerInfoList::unregisterTimers(QObject *object)
 {
     if (isEmpty())
         return false;
-    for (int i = 0; i < size(); ++i) {
-        QTimerInfo *t = at(i);
-        if (t->obj == object) {
-            // object found
-            removeAt(i);
+
+    auto associatedWith = [this](QObject *o) {
+        return [this, o](auto &t) {
+            if (t->obj == o) {
                 if (t == firstTimerInfo)
                     firstTimerInfo = nullptr;
                 if (t->activateRef)
                     *(t->activateRef) = nullptr;
                 delete t;
-            // move back one so that we don't skip the new current item
-            --i;
-        }
-    }
                 return true;
             }
+            return false;
+        };
+    };
+
+    qsizetype count = removeIf(associatedWith(object));
+    return count > 0;
+}
 
 QList<QAbstractEventDispatcher::TimerInfo> QTimerInfoList::registeredTimers(QObject *object) const
 {