[erlang-questions] Fwd: Report errors when using "-detached" option

Claes Wikstrom klacke@REDACTED
Tue Nov 18 20:47:31 CET 2008

ERLANG wrote:
> Hi Nicolas,
>>>> This is indeed a real problem. If daemon startup fails, you  
>>>> typically
>>>> want to indicate that through a call to exit(error_code) so that the
>>>> invoker can check $?
>>> Hmmm. Calling "exit(error_code)" isn't reported to the invoker.
>>> So $? always equals to 0.
>>> Is this an expected behaviour of calling "exit(error_code)" when  
>>> using
>>> "-detached" flag.
>> halt(error_code) works.
> No, It doesn't.

Yes it does,

[klacke@REDACTED]~ > erl
Erlang (BEAM) emulator version 5.6.5 [source] [smp:2] [async-threads:0] [kernel-poll:false]

Eshell V5.6.5  (abort with ^G)
1> halt(77).
[klacke@REDACTED]~ > echo $?

But that's not the point. What's needed is to fork(), let the new code run
for a while and check config/whatever, if all is well it calls foo:bar(ok) and the
invoker eventually gets a status code 0, whereas if the forked process (beam)
calls foo:bar({error, Code}) the invoker of erl -detached2 ... gets Code
in the UNIX shell


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