[erlang-questions] Erlang shell crashes

Thomas Lindgren <>
Mon Oct 30 18:15:59 CET 2006



--- Kostis Sagonas <> wrote:

> Although the analysis needed is not trivial, we
> (think we) know exactly 
> how to do this, but doing it never made it high on
> our priority list 
> partly due to lack of "real" test cases where such
> defect detection is 
> needed.  We would very much appreciate if Erlang
> users send us code 
> which suffers exactly from this type of problem.  We
> promise we will not 
> use this code for any other purposes.

How about checking the OTP code? A starter case might
be to analyze some variations on gen_server and
gen_fsm.

I believe Sven-Olof Nyström's analyzer derived
"mailbox types". I'm not sure how well this worked in
practice.

http://user.it.uu.se/~svenolof/SA/

Presumably, all you model checking people out there
also have wrestled with the basic problem. (Thomas
Arts or Lars-Ake Fredlund for instance?) Are there any
practical experiences to be told? 

> > You should also use a catch all message to remove
> any messages you were not expecting:
> > 
> > receive
> >   {From, expected_msg, Data} ->
> >         do_something(Data);
> >   AnyUnexpectedMsg ->
> >         log_and_skip_handling(AnyUnexpectedMsg)
> > end.
> 
> Doing this, of course solves this problem by
> potentially hiding it under 
> the carpet, right?

If one could tell the hypothetical analyzer to flag
messages or interactions that end up in the catch-all
clause, then we would both handle unexpected messages
at runtime (e.g., messages arriving from some other
node running who knows what) AND get warnings at
analysis-time.

Best,
Thomas



 
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