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

From: E. Gladyshev (eegg_at_[hidden])
Date: 2004-05-28 13:31:35

From: "Rob Stewart" <stewart_at_[hidden]>
> From: "E. Gladyshev" <eegg_at_[hidden]>
> > From: "Rob Stewart" <stewart_at_[hidden]>

[...]
> > > So, OK, there is that slight difference, but why would you care?
> >
> > I don't think that it is a slight difference. If you make an assumption
> > that all unhandled exceptions will eventually trigger
> > stack unwinding, but a specific implementation doesn't do that,
> > it is huge difference.
>
> Why would you want the non-deterministic behavior?

Whether I want it or not doesn't change anything.
All I am saying that it is implementation dependent and it is a big
difference.

[...]
>
> Why would you want terminate() to be called without stack
> unwinding on those platforms that do it?  What does that get you?
> I would think that boost::fsm's behavior, being more
> deterministic, would be preferable.

There could be many reasons, just to list few of them.
1. Some platforms pose non-C++ exceptions as normal C++ exception.
    You don't always want those platfrom specific exceptions trigger
    a whole bunch of stuff in your program.
2. Your design assumes that all possible exceptions are known
    and you handle them. So any unhandled exception is a bug.
    It is not safe to trigger stack unwinding in a buggy environment.

These reasons could be of a particular importance in
control applications where state machines are a must.

But again whether I want it or not, the Standard allows
implementation where the stack unwinding
(for unhandled exceptions) never happens.

[...]
> Does not unwinding the stack when terminate() is called, on
> whatever platforms do that, gain you something that outweighs the
> determinism and reuse of the boost::fsm approach?

Please see above.

Eugene