Re: [log4perl-devel] Logging from warn() and die(), but not during an eval {}

[J. D. B. <jd...@go...>]

On December 4, 2006, Mike Schilli wrote:

> >   wrapped, the exception that I wanted to ignore is now getting
> >   logged. I don't want that. I want it to be completely silent.
> >   (Failing that, I'd like to log it at a very low level.)
>=20
> Hmm, but if you want it to be completely silent, why aren't you simply
> resetting those handlers and then putting them back in place afterwards?
>=20
>     eval {
>         local $SIG{__WARN__} =3D 'IGNORE';
>         local $SIG{__DIE__}  =3D 'IGNORE';
>         # ... your code
>     };

  This doesn't help in the event that the eval is in a module I installed o=
ff of CPAN, which I can't practically modify to add that to the eval block.=
  (I could modify it, but it'd be wiped out at the next update, leading to =
a maintenance nightmare.)

  In this case I was dealing with evals in both places: my code, and a modu=
le.  I tried using local and setting the handler to 'DEFAULT', which seemed=
 to lead to more complex issues, and before I could fully trace through and=
 find out what was going on I found out about the eval in the module and de=
cided this was an untenable situation to try to fix.  So I gave up trying t=
o do a quick-and-dirty instrumentation of my code by using these handlers, =
and instrumented my code more directly.  Which is probably a good thing, al=
l in all.

> Alternatively, you could check if you're inside an eval{} (at some
> sublevel) by using code like
>=20
>     sub burried_in_eval {
>       my $i;
>=20
>       while(my ($pack, $file, $line, $sub) =3D caller($i++)) {
>          return 1 if $sub eq "(eval)";
>       }
>=20
>       return 0;
>     }
>=20
> and act accordingly in your sig handlers.

  Turns out there's an even easier way to do that.  $^S can be checked to s=
ee if code is in an eval.  Thinking through this yesterday afternoon I fina=
lly decided this wasn't a Log4perl issue, but a general Perl issue, because=
 really I think you'd almost never want those SIG handlers to fire when you=
're in an eval, trying to trap things before they become warnings and error=
s.  So I asked at use Perl; , and somebody pointed me to that variable.

  Since I wound up not using those handlers yesterday, it was a little too =
late, but I do still have a module called by this program and by others, an=
d I'll have to either instrument it as I did the main program, or go back a=
nd use the handlers.  (I'm thinking about doing both, for good measure.)

  Looks to me like the FAQ might want to change the text of those signal ha=
ndlers to include a check of $^S to decide whether to log or not.  And some=
body might like to package it all up in a module, which is what I was tryin=
g to do yesterday. :)

Thanks,
jdb