private void _checkpoint(HashMap<Checkpoint, Long> handles,
CompositeActor container) {
Iterator entities = container.entityList(Rollbackable.class).iterator();
while (entities.hasNext()) {
Rollbackable entity = (Rollbackable) entities.next();
Checkpoint checkpointObject = entity.$GET$CHECKPOINT();
if (!handles.containsKey(checkpointObject)) {
long handle = checkpointObject.createCheckpoint();
handles.put(checkpointObject, Long.valueOf(handle));
}
}