Trapped exits

Olivier BOUDEVILLE <>
Wed Feb 16 18:13:47 CET 2011


Hi,

I just have been bitten by the fact that apparently the code executed 
through "erl -eval" or "erl -run" will be executed by a process silently 
trapping exits by default (the opposite of when running it from the shell 
and of the default for spawned processes). 

Indeed, with:
"""
-module(foobar).
-export([ run/0 ]).
run() ->
      io:format( "Process ~w: ~p", [self(),process_info(self(),trap_exit)] 
).
"""

>From the shell we have as expected:
"""
> erl
Erlang R14B01 (erts-5.8.2) [source] [64-bit] [smp:8:8] [rq:8] 
[async-threads:0] [hipe] [kernel-poll:false]

Eshell V5.8.2  (abort with ^G)
1> c(foobar).
{ok,foobar}
2> foobar:run().
Process <0.31.0>: {trap_exit,false}ok
"""

whereas:

"""
> erl -eval 'foobar:run()'
Erlang R14B01 (erts-5.8.2) [source] [64-bit] [smp:8:8] [rq:8] 
[async-threads:0] [hipe] [kernel-poll:false]

Eshell V5.8.2  (abort with ^G)
1> Process <0.2.0>: {trap_exit,true}
"""

and 

"""
> erl -run foobar run
Erlang R14B01 (erts-5.8.2) [source] [64-bit] [smp:8:8] [rq:8] 
[async-threads:0] [hipe] [kernel-poll:false]

Process <0.2.0>: {trap_exit,true}Eshell V5.8.2  (abort with ^G)
"""

Maybe I have missed some references, but it does not seem much advertised!

And why trapping exits by default? Wouldn't it be safer to crash the 
spawned "initialization process" instead?

That means that when executing other processes in run/0, even thanks to 
spawn_link, EXIT messages might happily wait in the message queue of the 
run process and possibly remain unnoticed; a default policy which somewhat 
seems to violate both the "crash early" and "least astonishment" 
principles. Unless I made a mistake somewhere?

Thanks in advance for any hint,
Best regards,

Olivier Boudeville.
---------------------------
Olivier Boudeville

EDF R&D : 1, avenue du Général de Gaulle, 92140 Clamart, France
Département SINETICS, groupe ASICS (I2A), bureau B-226
Office : +33 1 47 65 59 58 / Mobile : +33 6 16 83 37 22 / Fax : +33 1 47 
65 27 13



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