Hi Richard,
since no one answered so far, I give a short answer:
> > 1) According to Snapshot semantics, snapshots are only
> taken inside an
> > alt statement...
>
> What about the following:
>
> pco1!send(X); pco1!send(Y);...
>
> is a snapshot taken after the first send?
No
(there is no need to force such an 'expensive' action
between two send operations)
>
> My second question is, what is a snapshot taken of? Ignoring
> timeout lists, variables etc, is it the whole PCO queue or
> just the top element of the PCO queue? The standard (TTCN-2)
> seems to imply (???) the whole queue, but existing tutorials
> (Wiles/Kroon TTCN restaurant tutorial for example in section
> 6.1) seem to suggest just the top element of the PCO queues.
> With a FIFO queue semantics it should not matter (but it
> should be clear in the operational semantics of the standard
> anyway B5.4.1 and B5.26), but I am in a project considering
> possible real time enhancements to TTCN-3 and one proposal we
> are kicking around is the possibility to prioritise certain
> time constrained events. This would only make sense if the
> snapshots were of the whole PCO queues and then some form of
> queueing were done other than FIFO, i.e. time constrained
> events were placed in front of non-time critical events.
>
A snapshot is considered to be a partial component state that
at least contains all information necessary to evaluate the
set of alternative in an alt statement (TTCN-3) or the set of
alternatives defined by the same level of indentation (TTCN-2).
Forcing implementations to collect information that is not needed,
e.g., the entire queue contents, makes no sense.
(However, as main writers of the operational semantics for TTCN-3
I must admit that the snapshot is not implemented correctly in
the semantics, but I hope that we can fix this soon.)
If you need to reorder the FIFO queues, you should do it before
taking a snapshot, or used different ports for different
priorities and order the receiving events according to these
priorities.
Hope that helps for the moment
Jens
> Thanks for any responses,
>
> Rich
>
> Dr Richard Sinnott
> Ericsson EPK Karlskrona
> Email: This email address is being protected from spambots. You need JavaScript enabled to view it.
> Mobile: +46-(0)70-690-6007
>