the sub-process wont exit until the parent does

[sleepy_11]

Perl 5.10.1 on CentOS 6.8

First official project on Perl and get a issue with Perl fork. The parent process is a daemon and it folks child process and end it after the task is done. But the reality is the child process won't quit.

Since with Moose, totally 3 pieces of code. The expected result is the Kitty object will quit right after the PapaCat process calls the close to kill it.

Below is the demo code:

pipe_test.pl

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

use PapaCat;
use Data::Dumper;

my $obj = new PapaCat();

$obj->pipe_test();

PapaCat.pm

package PapaCat;
use strict;
use warnings FATAL => 'all';

use Moose;
use Kitty;
use FileHandle;
use Data::Dumper;

sub pipe_test {
        my $self = shift;

        pipe(my $fh_from, my $fh_to);
        $fh_to->autoflush(1);

        my $pid;
        my $obj = Kitty->new(fh_to=>$fh_to);

        if (!($pid = fork())) {
                $obj->meow();
                exit();
        } elsif (!defined($pid)){
                #fork failed
                print "fail:fork retuns with error.\n";
                return;
        }

        $obj->pid($pid);
        my $result = readline($fh_from);
        print $result;

        $obj->close();
        close $fh_to;

        sleep(1000);  # make sure the parent won't quit first
}

1;

Kitty.pm

package Kitty;
use strict;
use warnings FATAL => 'all';

use Moose;
use Data::Dumper;

sub meow {
        my $self = shift;

        my $mm = $self->_fh_to;
        print $mm ("Meow!\n");
}

sub close {
        my $self = shift;

        print "bb:".Dumper($self). "\n";
        if (kill(0, $self->pid)) {
                kill(15, $self->pid);
        }

        CORE::close($self->_fh_to);
        delete $self->{pid};
        print "  closed";
}

has '_fh_to' => (
        is         => 'rw',
        init_arg   => 'fh_to',
);

has 'pid' => (
        is => 'rw',
);

1;

[salva]

waitpid!

[haukex]

It's been a while since I worked with raw forking instead of a helper module, but as far as I can tell, your process isn't actually backgrounding itself nor waiting on its children. If you want to implement this yourself, I suggest a thorough read of perlipc.

For doing parallel processing, Parallel::ForkManager is something I see recommended often.

At the moment, I mostly use Daemon::Control for my daemons, and a while back I also used Daemon::Daemonize. See also the FAQ How do I fork a daemon process?, which recommends Proc::Daemon. Alternatively, although I unfortunately haven't yet had a chance to try it out, fellow monk afoken often recommends daemontools.

[mr_mischief]

If you're not using something like Parallel::ForkManager then you should be using wait or waitpid to wait for your child processes. You should also investigate $SIG{'CHLD'} and determine what you want for that. If you're writing from one to the other, also consider $SIG{'PIPE'}.

If you haven't, read up on perlipc (or perldoc perlipc or man perlipc) to learn some other stuff. Also, I can definitely recommend APUE and Unix Network Programming, Volume 2: Interprocess Communication. Advanced Unix Programming by Rochkind, The Unix Programming Environment by Kernighan and Pike, and lots of other material exist that could help, too.

[sleepy_11]

Thanks all your info. I think all 3 ways will fix this issue. And so far, I tried the " $SIG{'CHLD'}", and it works.

I will go through the material as suggested