On Fri, May 28, 2004 at 12:29:01AM +0200, Andreas Huber wrote:
No, that would be wrong. UML requires that in a self-transition the exit and the entry action is called (see StopWatch for an example where such a transition makes sense). This is not the case for an in-state reaction.
What UML requires is not necessarily what is good for a generic FSM framework. The UML model is IMHO over complex and probably broken. An example is entry and exit actions for states. It is some what oxymoronic that a single state should actually consist of three sub-states because of entry and exit actions. The idea that they must be paired is particularly strange as one of the most common uses of the concept in the networl protocol work that I am familar with is prior to entering the idle stae some initialisation work is necessary and prior to re-entering an idle state from an exit event we want to do some clean-up. This whole concept is much better modeled *IMHO* by transitory states. These have the advantage that they do not have to be paired and they allow same/self-transition to be a no-op which is a very common requirement. Classical FSM's are a mapping from state/event pairs to behaviour and transitions. The Idea that a state should maintain its own data and thereby become stateful also seems to be bad modeling and against the KISS principle. My comments are based, so far, are based on a breif reading of the documentation and I plan to re-read it more carefully along with the implementation and provide further feedback. My gut feel is that this framework is too heavy weight and a one size fits all solution. Whereas I think that an FSM equivelent to STL collections would be a better approach. There are two other approaches to FSM's that do not apear to be discussed in the rationale; Herb Sutter, in an article hints at using boost::function for FSM's and the GOF state pattern tals of using singleton, flyweight states which are re-enterant and therefore offer exelent MT performance. /ikh