Re^2: Setting signal handlers considered unsafe?

Just tried on my home Ubuntu system (perl 5.8.8). Ran for a few seconds (a new record!) and crashed with

Unable to create sub named "" at crash.pl line 15.
[download]

This is the exact code I used:

#!/usr/bin/perl

use warnings FATAL => qw( all );
use strict;

use POSIX qw( :signal_h );

$SIG{ALRM} = sub { print "SIGARLM: main handler\n" };

sub f {
        my $sigset = POSIX::SigSet->new;
        my $blockset = POSIX::SigSet->new( SIGALRM );

        sigprocmask(SIG_BLOCK, $blockset, $sigset );
        local $SIG{ALRM} = sub { print "SIGALRM\n" }; # line 15
        sigprocmask(SIG_SETMASK, $sigset );
}

if (fork) {
        # parent
        f while 1;
} else {
        # child
        sleep 1;
        print "child starting\n";
        1 while kill ALRM => getppid;
}
[download]

Comment on Re^2: Setting signal handlers considered unsafe? Select or Download Code

Replies are listed 'Best First'.
Re^3: Setting signal handlers considered unsafe? by TGI (Parson) on Nov 05, 2008 at 23:32 UTC
I'm no master of perlguts either, but it occurs to me that there are two places where you are vulnerable to signal changes: 1. when you set the localized handler, 2. when the localization goes out of scope and the old handler is installed. Your code traps only one of the two vulnerable points. What happens if you do: #!/usr/bin/perl use warnings FATAL => qw( all ); use strict; use POSIX qw( :signal_h ); $SIG{ALRM} = sub { print "SIGARLM: main handler\n" }; sub f { my $sigset = POSIX::SigSet->new; my $blockset = POSIX::SigSet->new( SIGALRM ); my $old_handler = $SIG{ALRM}; # Install new handler sigprocmask(SIG_BLOCK, $blockset, $sigset ); $SIG{ALRM} = sub { print "SIGALRM\n" }; # line 15 sigprocmask(SIG_SETMASK, $sigset ); # spin a bit. my $x; $x = $_ for 1..10; # Restore old handler. sigprocmask(SIG_BLOCK, $blockset, $sigset ); $SIG{ALRM} = $old_handler; sigprocmask(SIG_SETMASK, $sigset ); } if (fork) { # parent f while 1; } else { # child sleep 1; print "child starting\n"; 1 while kill ALRM => getppid; } [download] TGI says moo	[reply] [d/l]
Re^3: Setting signal handlers considered unsafe? by ig (Vicar) on Nov 11, 2008 at 17:41 UTC
On my system (This is perl, v5.8.8 built for i386-linux-thread-multi) your script ran for many minutes, until I stopped it. I am running CentOS 5.2 with the CentOS distribution of perl. Is it possible that your system is not running with safe/deferred signals (environment variable PERL_SIGNALS set to "unsafe")?	[reply]
Re^4: Setting signal handlers considered unsafe? by gnosek (Sexton) on Nov 12, 2008 at 13:24 UTC
Is it possible that your system is not running with safe/deferred signals (environment variable PERL_SIGNALS set to "unsafe")? No. Rather not. All my perl binaries are distribution-provided (`perl -V \| grep -i sig` only returns `hint=recommended, useposix=true, d_sigaction=define`) and I don't have anything containing 'PERL' in my environment either. The plot thickens... ;)	[reply]