Front page | perl.perl5.porters |
Postings from May 2016
On Wed, May 04, 2016 at 11:43:45AM +0100, Nicholas Clark wrote:
> On the assumption that this fixes the actual problems that Coro hit,
> short of test cases to demonstrate otherwise.
I suspect that *this* is the bug that Coro hit.
For $whatever reason, PerlIO_find_layer() chooses to silence all warnings,
and implements this by localising PL_warnhook and then assigning a no-op sub
to it. The problem is that this isn't reflected in %SIG, so when Perl-space
code localises $SIG{__WARN__}, the previous value of $SIG{__WARN__} is
stored on the scope stack as the thing to write back at scope exit:
$ cat ~/test/via.pl
#!/usr/bin/perl -w
use strict;
unshift @INC, sub {
return undef unless caller eq "main";
return \<<'EOP';
print STDERR "This code is being called\n";
warn "My errors are eaten";
{
local $SIG{__WARN__} = sub {
my $message = shift;
chomp $message;
print STDERR "Warning you about '$message'\n";
};
warn "Christmas";
}
warn "This error message should still be eaten";
EOP
};
PerlIO::Layer->find("Noisy", 1);
__END__
$ ./perl -Ilib ~/test/via.pl
This code is being called
Warning you about 'Christmas at /loader/0xb99c00/PerlIO.pm line 12.'
This error message should still be eaten at /loader/0xb99c00/PerlIO.pm line 15.
Remove the local $SIG{__WARN__} and that last warning is correctly suppressed.
Nicholas Clark