[erlang-questions] Prevent my crashing gen_server to produce any error message

[Siri Hansen]

There are several different types of reports for a crashing process:

1) for gen* behaviours (gen_server, gen_event, gen_statem, ...), you get an
error report issued by the crashing process just before it dies. For a
gen_server, these messages start with " ** Generic server <...>
terminating". These can be silenced with the process metadata + filter I
suggested in my previous mail.

2) for gen* behaviours and other processes started with proc_lib, you get a
crash report issued from the crashing process just before it dies. These
reports (by default) have the heading == CRASH REPORT==, and the message
starts with "crasher: ". These can be silenced with the process metadata +
filter I suggested in my previous mail.

3) If the crashed process was part of a supervisor tree, a supervisor
report is issued from the process' parent, that is, its supervisor. These
reports (by default) have the heading == SUPERVISOR REPORT ==, and the
message contains "errorContext: child_terminated". Since they are issued
from a different process, these are not silenced by the suggested filter.

4) If the crashed process is not a gen* behaviour, and it is not started by
proc_lib, then the emulator issues an error report which starts with "Error
in process <...> with exit value:". These are not silenced by the suggested
filter.

These are the ones I can think of right now - and I assume that what you
see are the supervisor reports only. Is this correct?

How to silence the supervisor report depends on what you want to see from
other processes. You can turn off supervisor reports with errorContext
child_terminated completely for your system with this filter:

logger:add_primary_filter(stop_sup_reports,{fun(#{log:=#{label:={supervisor,child_terminated}}},_)
-> stop; (_,_) -> ignore end, ok}).

or for one specific supervisor (fah_sup) with this one:

logger:add_primary_filter(stop_sup_reports,{fun(#{msg:={report,#{label:={supervisor,child_terminated},report:=R}}},_)
-> case proplists:get_value(supervisor,R) of {local,fah_sup} -> stop; _ ->
ignore end; (_,_) -> ignore end, ok}).

If the supervisor has other types of children, you might want to silence
the reports related to one specific child id (fah) only. Then you can use
this filter:

logger:add_primary_filter(stop_sup_reports,{fun(#{msg:={report,#{label:={supervisor,child_terminated},report:=R}}},_)
-> Child = proplists:get_value(offender,R), case
proplists:get_value(id,Child) of fah -> stop; _ -> ignore end; (_,_) ->
ignore end, ok}).

Since I don't know much about what your system does and needs, these are
only a few ideas. Another possibility can be to turn off all so called
"SASL reports" completely - this would silence reports 2) and 3) for all of
your system - if that is acceptable.

The pid-idea from my first mail would only be needed for the emulator logs,
4) in my listing above, which I don't believe you see?



>> Maybe this:
>>
>> logger:add_primary_filter(my_filter_id,{fun(#{meta:=#{label:={proc_lib,crash}}})
>> -> stop; (_,_) -> ignore end,ok}).
>>
>> ?
>>
>>
I assume Len meant to put 'msg' instead of 'meta' here. That would work,
but it would silence the crash reports, 2) in my listing above, from all
processes, not only the specific ones.

I hope this is of some help!
Kind Regards
/siri


>>
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>> Led
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