Cache a state's parent state

QAbstractState::parentState() is called heavily by the state machine
algorithm. The parent state is obtained by qobject_cast'ing
QObject::parent(). qobject_cast() is expensive. This commit introduces
caching of the result in order to improve performance.

We expect that the cache won't be invalidated much since the parent-child
relationship of states usually doesn't change after the state machine is
started.

Reviewed-by: Eskil Abrahamsen Blomfeldt

1 files changed, 9 insertions, 0 deletions

diff --git a/tests/auto/qstatemachine/tst_qstatemachine.cpp b/tests/auto/qstatemachine/tst_qstatemachine.cpp
index 97057c659f..975b3012db 100644
--- a/tests/auto/qstatemachine/tst_qstatemachine.cpp
+++ b/tests/auto/qstatemachine/tst_qstatemachine.cpp
@@ -117,6 +117,7 @@ private slots:
     void cleanup();
 
     void rootState();
+    void machineWithParent();
     void addAndRemoveState();
     void stateEntryAndExit();
     void assignProperty();
@@ -1045,6 +1046,14 @@ void tst_QStateMachine::rootState()
     QCOMPARE(s2->parentState(), static_cast<QState*>(&machine));
 }
 
+void tst_QStateMachine::machineWithParent()
+{
+    QObject object;
+    QStateMachine *machine = new QStateMachine(&object);
+    QCOMPARE(machine->parent(), &object);
+    QCOMPARE(machine->parentState(), (QObject*)0);
+}
+
 void tst_QStateMachine::addAndRemoveState()
 {
 #ifdef QT_BUILD_INTERNAL