Re: catching errors from linked processes: simplest way?

You could add some supervision to the client by using a toplevel catch. 
Then you will get a stack dump. The following code also demonstrates a 
line number macro trick with the process dictionary that is possible if 
you have a toplevel catch in the client.

Runtime result:
21> test:top().
{'EXIT',{{badmatch,b},
         [{test,foo,0},
          {test,do,0},
          {test,top,0},
          {erl_eval,expr,3},
          {erl_eval,exprs,4},
          {shell,eval_loop,2}]}} at test:22
error

/ Raimo Niskanen, Erlang/OTP, Ericsson AB



-module(test).
-export([top/0]).

-define(line, put(location,{?MODULE,?LINE}),).

top() ->
    ?line
        case catch do() of
            {'EXIT',_} = Exit ->
                {Module,Line} = get(location),
                io:format("~p at ~w:~w~n", [Exit,Module,Line]),
                error;
            Result ->
                {ok,Result}
        end.

do() ->
    ?line foo(),
    ?line bar().

foo() ->
    ?line a=b.

bar() ->
    ok.



Chris Pressey wrote:
> On Tue, 22 Apr 2003 15:35:16 -0500
> Chris Pressey <cpressey@xxxxxxxxxxxxx> wrote:
>
>
> > If I do the translation in the client, I would have:
> >
> >  foo(A, B) ->
> >    case A of
> >      true ->
> >        bar(B);
> >      false ->
> >        throw(only_applies_under_condition_a)
> >    end.
> >
> > which is hardly any improvement over the original.
>
>
> Ah!  I think I see a compromise: notify the supervisor of the nature of
> any potential upcoming errors.  So the code becomes something like:
>
>   foo(A, B) ->
>     supervisor:potential_error(only_applies_under_condition_a, [A,B]),
>     A = true, bar(B).
>
> where supervisor:potential_error/2 sends a message to the supervisor,
> which stores it in a dictionary using the pid the message came from as
> the key, and which retrieves it when an error actually does occur.
>
> The code is still fairly easy to read, and the supervisor doesn't need
> to know about the structure of the code it's supervising, yet it can
> know some details about what state the process was in when it crashed. 
>
> Sweet!
>
> -Chris