Sequential trace in match specification problems..

Francesco Cesarini <>
Tue Nov 13 15:01:06 CET 2001


For those interested, the strange behaviour of the seq_trace in the
shell (and in my example) was because of all the internal io messages
between the shell and its group leader which were resetting the trace
tokens. Using dbg:p(new, [c]) does not reset the token. Another (and
obvious solution) is to set the token internally in process a once the
initial message has been received.  (It might be worth putting a note of
the io disturbances in the shell in the documentation.)

Thanks everyone.

Francesco

Francesco Cesarini wrote:

> Hello everyone,
> I am having problems with sequential tokens. (For those of
> you who have never used them, take a look at them as it is
> an excellent addition to the trace capabilities which came
> out with R7). I have been getting problems/strange
> behaviours when I try to set tokens in the shell. The major
> problem, however, seems to set trace tokens with match
> specifications. The match specification is triggered, (I
> have printed stuff out, valid trace tokens included), but
> the trace tokens are not associated with the tokens.
>
> sequence:start() spawns three processes, and registers
> them. When process a receieves a start message, it sends a
> message to b and c, which in turn send a message to a.
> sequence:start_tracer() receives messages and prints them
> out. I have played around with the syntax, but to no avail.
> Nor have I found any documentatins on restrictions. Help
> anyone?
>
> Thanks!
> Francesco
>
> --
> 2> sequential:start_tracer().
> false
> 3> dbg:p(new, [c,m]).
> {ok,[{matched,0}]}
> 4> (<0.37.0>) <0.20.0> ! {io_request,<0.37.0>,
>                                   <0.20.0>,
>                                   {get_until,
>                                       {format,"~w> ",[4]},
>                                       erl_scan,
>                                       tokens,
>                                       [1]}}
> 4> sequential:start().
> (<0.37.0>) << {io_reply,<0.20.0>,
>                         {ok,[{atom,1,sequential},
>                              {':',1},
>                              {atom,1,start},
>                              {'(',1},
>                              {')',1},
>                              {dot,1}],
>                             2}}
> (<0.37.0>) << timeout
> true
> 5> (<0.42.0>) <0.20.0> ! {io_request,<0.42.0>,
>                                   <0.20.0>,
>                                   {get_until,
>                                       {format,"~w> ",[5]},
>                                       erl_scan,
>                                       tokens,
>                                       [1]}}
> 5> a ! start.
> (<0.42.0>) << {io_reply,<0.20.0>,
>                         {ok,[{atom,1,a},{'!',1},
> {atom,1,start},{dot,1}],2}}
> (<0.42.0>) << timeout
> start
> (<0.41.0>) << start
> 6> (<0.41.0>) b ! start
> 6> (<0.40.0>) << start
> 6> (<0.40.0>) c ! init
> 6> (<0.39.0>) << init
> 6> (<0.40.0>) d ! init
> 6> (<0.38.0>) << init
> 6> (<0.39.0>) a ! ok
> 6> (<0.41.0>) << ok
> 6> (<0.38.0>) a ! ok
> 6> (<0.41.0>) << ok
> 6> (<0.43.0>) <0.20.0> ! {io_request,<0.43.0>,
>                                   <0.20.0>,
>                                   {get_until,
>                                       {format,"~w> ",[6]},
>                                       erl_scan,
>                                       tokens,
>                                       [1]}}
> 6>

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