INT signal kills process run with expect, when $SIG{'INT'} is set

ISAI student has asked for the wisdom of the Perl Monks concerning the following question:

Hello all. I am trying to ramp up a new utility, which accepts a ^C from the user, outputs running processes (ran by the script), and asks for the user prompt. I have tried something very simple. I spawn a sleep process, via Expect, and every time that I hit ^C, I expect PERL to output a message. The code is:

require Expect;
use strict;
$SIG{'INT'}=sub {print "Al Bundy rules!\n";};
$SIG{CHLD}='IGNORE';
my $proc=Expect->spawn("sleep 10");
unless ($proc->expect(10,"Mommy")) {
    print "Stop selling women shoes\n"; 
}
[download]

Whe I hit ^c once, I get:

liord@analog2 238 > tester.pl
Al Bundy rules!
Stop selling women shoes
[download]

And the script exits. I have expected the scipt NOT to exit after one ^c, but after n presses (or 10 seconds). What am I doing wrong? PERL version is: This is perl, v5.8.8 built for x86_64-linux-thread-multi

Comment on INT signal kills process run with expect, when $SIG{'INT'} is set Select or Download Code

Replies are listed 'Best First'.
Re: INT signal kills process run with expect, when $SIG{'INT'} is set by salva (Canon) on Feb 22, 2011 at 09:34 UTC
That happens because pressing CTRL-C at the terminal does not send the kill signal just to the process but to the full process group. The workaround is to get `setpgrp` called between the `fork` and `exec` calls used internally to spawn the process... and that probably means writing your own `spawn` method.	[reply] [d/l] [select]
Re: INT signal kills process run with expect, when $SIG{'INT'} is set by ISAI student (Scribe) on Feb 22, 2011 at 08:34 UTC
It's actually kills even w/o Expect. Code below is killed with ^c too: `require Expect; use strict; $SIG{'INT'}=sub {print "Al Bundy rules!\n";}; sleep 10000;` [download] The prcess lasts until 1st ^c.	[reply] [d/l]
Re^2: INT signal kills process run with expect, when $SIG{'INT'} is set by cdarke (Prior) on Feb 22, 2011 at 09:05 UTC
On many platforms sleep will exit on any signal, including SIGINT. You need to place it in a loop. For example: `use warnings; use strict; $SIG{'INT'}=sub {print "Clive Darke rules!\n";}; while (1) { sleep 10000; }` [download]	[reply] [d/l]
Re: INT signal kills process run with expect, when $SIG{'INT'} is set by ikegami (Patriarch) on Feb 22, 2011 at 16:53 UTC
It doesn't kill the process, handled signals interrupt `sleep`. If they didn't, the handler wouldn't get to run. See Re: fork() doesn't care about my sleep()? for how to make sleep uninterruptible. The OP didn't (visibly) use a `sleep` in the process that has a signal handler, so this isn't (likely to be) the OP's problem.	[reply] [d/l] [select]