[boost] Re: [prereview request][fsm]

From: Andreas Huber (ah2003_at_[hidden])
Date: 2004-05-27 03:20:15

E. Gladyshev <eegg <at> comcast.net> writes:

> If the entry or exit action throws, the state machine is in undefined
> state...
> unless you define the throw event as a legitimate event
> which causes a transition. However I don't see how
> this can be done generically.

boost::fsm does exactly this and in a generic fashion.

> In our project, we decided:
> 1. The state machine *framework* never catches user exceptions.
> 2. The framework doesn't have a concept of failed actions at all.
>     Any action has to be completed.

This is the traditional way of dealing with failures in state machines. It 
works, but it is cumbersome.

> All fault situations during an action are *expected* and it
> is a responsibility of this action to generate an appropriate
> event that will cause a transition to a fault handling state or
> stop the process.

Why not let the exception slip out of the action and let the state machine 
framework:
1. catch the exception
2. generate an appropriate event
3. dispatch that event to the appropriate state (see docs for details)
4. check that the event has indeed been processed and that the machine is back 
in a stable state

?

Regards,

Andreas