Cache QState's child states

This is the same type of optimization as that done for transitions in
commit 5d8dcd57cd13fdd9c8643fa3bdda9f197a4351ff. The idea is to avoid
calling qobject_cast() because it's very expensive.

Obtaining child states needs to be as fast as possible because it's in
the critical path of the state machine algorithm; it's called by a ton
of internal functions, like isCompound(), isAtomic(), isInFinalState().
It's also called heavily for parallel state groups.

Reviewed-by: Eskil Abrahamsen Blomfeldt

2 files changed, 17 insertions, 10 deletions

diff --git a/src/corelib/statemachine/qstate.cpp b/src/corelib/statemachine/qstate.cpp
index 9abf20b..bcd8364 100644
--- a/src/corelib/statemachine/qstate.cpp
+++ b/src/corelib/statemachine/qstate.cpp
@@ -125,7 +125,7 @@ QT_BEGIN_NAMESPACE
 
 QStatePrivate::QStatePrivate()
     : errorState(0), initialState(0), childMode(QState::ExclusiveStates),
-      transitionsListNeedsRefresh(true)
+      childStatesListNeedsRefresh(true), transitionsListNeedsRefresh(true)
 {
 }
 
@@ -181,15 +181,18 @@ QState::~QState()
 
 QList<QAbstractState*> QStatePrivate::childStates() const
 {
-    QList<QAbstractState*> result;
-    QList<QObject*>::const_iterator it;
-    for (it = children.constBegin(); it != children.constEnd(); ++it) {
-        QAbstractState *s = qobject_cast<QAbstractState*>(*it);
-        if (!s || qobject_cast<QHistoryState*>(s))
-            continue;
-        result.append(s);
+    if (childStatesListNeedsRefresh) {
+        childStatesList.clear();
+        QList<QObject*>::const_iterator it;
+        for (it = children.constBegin(); it != children.constEnd(); ++it) {
+            QAbstractState *s = qobject_cast<QAbstractState*>(*it);
+            if (!s || qobject_cast<QHistoryState*>(s))
+                continue;
+            childStatesList.append(s);
+        }
+        childStatesListNeedsRefresh = false;
     }
-    return result;
+    return childStatesList;
 }
 
 QList<QHistoryState*> QStatePrivate::historyStates() const
@@ -473,8 +476,10 @@ void QState::setChildMode(ChildMode mode)
 bool QState::event(QEvent *e)
 {
     Q_D(QState);
-    if ((e->type() == QEvent::ChildAdded) || (e->type() == QEvent::ChildRemoved))
+    if ((e->type() == QEvent::ChildAdded) || (e->type() == QEvent::ChildRemoved)) {
+        d->childStatesListNeedsRefresh = true;
         d->transitionsListNeedsRefresh = true;
+    }
     return QAbstractState::event(e);
 }
 
diff --git a/src/corelib/statemachine/qstate_p.h b/src/corelib/statemachine/qstate_p.h
index 3b5f416..34c8838 100644
--- a/src/corelib/statemachine/qstate_p.h
+++ b/src/corelib/statemachine/qstate_p.h
@@ -99,6 +99,8 @@ public:
     QAbstractState *errorState;
     QAbstractState *initialState;
     QState::ChildMode childMode;
+    mutable bool childStatesListNeedsRefresh;
+    mutable QList<QAbstractState*> childStatesList;
     mutable bool transitionsListNeedsRefresh;
     mutable QList<QAbstractTransition*> transitionsList;