Re^4: Child process dies

Why the sleep 1 for 1 .. 100;? My ignorance really; I wasn't sure whether the script, like my daughter, would sleep through the alarm so I decided to try lots of small sleeps after it didn't work with one long sleep.

I was already trying things like explicitly closing the pipe in the parent if it caught a signal. Following your post I have modified the script so the child keeps printing a "heartbeat" to the pipe but still to no avail. Here's the modified script.

use strict;
use warnings;

use IO::Pipe;
my $pipeFH;

my $rcHandler = sub {$pipeFH->close(); exit;};

$SIG{INT} = $rcHandler;
$SIG{QUIT} = $rcHandler;
$SIG{TERM} = $rcHandler;

print qq{Parent PID $$\n};
$pipeFH = IO::Pipe->new();

my $pid;
if ($pid = fork)
{
    $pipeFH->reader();
    print qq{Kid is PID $pid\n};
}
elsif(defined($pid))
{
    $SIG{PIPE} = sub {exit;};
    $pipeFH->writer();
    $pipeFH->print(qq{Kid: Snoozing\n});
    for my $heartbeat ( 1 .. 30 )
    {
        $pipeFH->print(qq{Kid: Heartbeat $heartbeat\n});
        sleep 1;
    }
    
    $pipeFH->print(qq{Kid: Waking\n});
    print qq{Kid: Quitting\n};
    exit;
}

while ((my $returnPid = wait) != -1)
{
    print qq{Kid $returnPid returned\n};
}

while (defined(my $line = $pipeFH->getline()))
{
    print qq{Read: $line};
}
[download]

I had been killing the parent with a kill -15 (TERM) from another shell but I noticed that the child does go away immediately if I Ctrl-C the running parent. Is it the case that child processes also get an INT if the parent gets one from the shell?

Cheers,

JohnGG

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Re^5: Child process dies by polettix (Vicar) on Jan 05, 2007 at 23:58 UTC
Update In the code below the main difference with respect to johngg's version is the use of the straight pipe function instead of IO::Pipe. It turned out (thanks to johngg's tests) that using straight pipes allowed him to trap the PIPE signal, which he couldnt' using the module. I tried to peek into the module and found nothing about SIGPIPE trapping, but I didn't dig this up to the modules included by IO::Pipe. Linux box with a slightly modified version of your script, and the parent signalled from another shell: #!/usr/bin/perl use strict; use warnings; my $whoami; sub handler { print {STDERR} "$whoami: handler [@_]\n"; exit 0; } $SIG{INT} = \&handler; $SIG{QUIT} = \&handler; $SIG{TERM} = \&handler; $SIG{PIPE} = \&handler; END { print {STDERR} "$whoami in END block\n"; } print {STDERR} qq{Parent PID $$\n}; pipe my $r, my $w; my $pid; if ($pid = fork) { $whoami = 'parent'; close $w; print {STDERR} qq{Kid is PID $pid\n}; while (<$r>) { print {STDERR} "parent received: $_"; } print {STDERR} "parent exiting normally\n"; exit 0; } ## end if ($pid = fork) elsif (defined($pid)) { select $w; $\|++; $whoami = 'kid'; close $r; print {$w} qq{Kid: Snoozing\n}; for my $heartbeat (1 .. 30) { print {$w} qq{Kid: Heartbeat $heartbeat\n}; sleep 1; } print {$w} qq{Kid: Waking\n}; print {STDERR} qq{Kid: Quitting\n}; exit; } ## end elsif (defined($pid)) __END__ poletti@PolettiX:~/sviluppo/perl$ perl johngg.pl Parent PID 5336 Kid is PID 5337 parent received: Kid: Snoozing parent received: Kid: Heartbeat 1 parent received: Kid: Heartbeat 2 parent received: Kid: Heartbeat 3 parent received: Kid: Heartbeat 4 parent received: Kid: Heartbeat 5 parent: handler [TERM] parent in END block poletti@PolettiX:~/sviluppo/perl$ kid: handler [PIPE] kid in END block [download] Note that after the parent exits the shell regains control, hence the prompt. Within a second, the kid is trying to write to the pipe and gets signalled. Also note the following run (stopped with CTRL-C): `poletti@PolettiX:~/sviluppo/perl$ perl johngg.pl Parent PID 5348 Kid is PID 5349 parent received: Kid: Snoozing parent received: Kid: Heartbeat 1 parent received: Kid: Heartbeat 2 parent received: Kid: Heartbeat 3 parent: handler [INT] parent in END block kid: handler [INT] kid in END block` [download] Both processes get the INT signal: probably the shell sends the signal to the whole process group. Flavio perl -ple'$_=reverse' <<<ti.xittelop@oivalf Don't fool yourself.*	[reply] [d/l] [select]

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Re^5: Child process dies
by polettix (Vicar) on Jan 05, 2007 at 23:58 UTC

Update

Linux box with a slightly modified version of your script, and the parent signalled from another shell:

#!/usr/bin/perl
use strict;
use warnings;

my $whoami;

sub handler {
   print {*STDERR} "$whoami: handler [@_]\n";
   exit 0;
}
$SIG{INT}  = \&handler;
$SIG{QUIT} = \&handler;
$SIG{TERM} = \&handler;
$SIG{PIPE} = \&handler;

END {
   print {*STDERR} "$whoami in END block\n";
}

print {*STDERR} qq{Parent PID $$\n};
pipe my $r, my $w;

my $pid;
if ($pid = fork) {
   $whoami = 'parent';
   close $w;
   print        {*STDERR} qq{Kid is PID $pid\n};
   while (<$r>) {
      print {*STDERR} "parent received: $_";
   }
   print {*STDERR} "parent exiting normally\n";
   exit 0;
} ## end if ($pid = fork)
elsif (defined($pid)) {
   select $w;
   $|++;
   $whoami = 'kid';
   close $r;
   print {$w} qq{Kid: Snoozing\n};
   for my $heartbeat (1 .. 30) {
      print {$w} qq{Kid: Heartbeat $heartbeat\n};
      sleep 1;
   }
   print {$w} qq{Kid: Waking\n};
   print {*STDERR} qq{Kid: Quitting\n};
   exit;
} ## end elsif (defined($pid))

__END__

poletti@PolettiX:~/sviluppo/perl$ perl johngg.pl
Parent PID 5336
Kid is PID 5337
parent received: Kid: Snoozing
parent received: Kid: Heartbeat 1
parent received: Kid: Heartbeat 2
parent received: Kid: Heartbeat 3
parent received: Kid: Heartbeat 4
parent received: Kid: Heartbeat 5
parent: handler [TERM]
parent in END block
poletti@PolettiX:~/sviluppo/perl$ kid: handler [PIPE]
kid in END block
[download]

Note that after the parent exits the shell regains control, hence the prompt. Within a second, the kid is trying to write to the pipe and gets signalled. Also note the following run (stopped with CTRL-C):

poletti@PolettiX:~/sviluppo/perl$ perl johngg.pl
Parent PID 5348
Kid is PID 5349
parent received: Kid: Snoozing
parent received: Kid: Heartbeat 1
parent received: Kid: Heartbeat 2
parent received: Kid: Heartbeat 3
parent: handler [INT]
parent in END block
kid: handler [INT]
kid in END block
[download]

Both processes get the INT signal: probably the shell sends the signal to the whole process group.

Flavio
perl -ple'$_=reverse' <<<ti.xittelop@oivalf

Don't fool yourself.

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