RE: SDL-News: How to save signal during transtion?

Subject: RE: SDL-News: How to save signal during transtion?
Date: Thu Oct 25 2001 - 14:22:09 GMT

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You may save signal_3 by describing a separate flow with an asterisk
and a save.
SAVE signal_3;
This will save signal_3 in all states not explicitly consuming this signal.
I hope that this will solve your problem.
Best regards,
John Svensson
John Svensson
Training Resource Manager
Telelogic Sverige AB
P O Box 4128 phone: +46 40-17
47 45
SE-203 12 Malm? fax: +46 40-17 47 47

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This is what actually occurs with your current specification :
1. In state A, signal 3 arrives and is saved.
2. In state A, signal 2 arrives, BUT can't be handled in that state : so
it's discarded.
(note that until now, the actual first message of your queue is still
S3, but because of the SAVE clause, it can't be consumed while the
process remains in state A)
3. In state A again, signal 1 arrives, and can be handled. S1 is
consumed, and the state of your process is now B.
4. Since the process has reached a new state, maybe in that state
there's no reason to block some saved signals anymore. And that's the
case here, S3 is not supposed to be saved in state B, so it's consumed
(unfortunately, it is destroyed in fact, because nothing says in state B
how to handle S3...)
5. OK, now your queue is really empty, and no more message arrives. So
you are stuck into state B, and your important signal is gone to the
trashcan :-(
Solution : SAVE S3 in state B : the benefit of this is that you do not
discard your precious signal 3 in state B, BUT you are still stuck in
state B forever!
If you really need to handle S3 in state C, you also have to SAVE S2 in
state A, because S2 is your only chance to reach state C some day :-)
And for the moment, S2 is destroyed in state A...

Rick Reed, TSE Limited
13 Weston House, 18-22 Church Street
Lutterworth Leicestershire LE17 4AW United Kingdom
Tel +44 14 55 55 96 55; Fax +44 14 55 55 96 58
Mob +44 79 70 50 96 50
email: (please reply to this address)

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