basic-supervisor-sigaction.pl

#!/usr/bin/env perl

use v5.10;
use warnings;
use strict;

use EV;
use AnyEvent;
use POSIX qw();

use Sys::Hostname qw(hostname);

main();

sub main {
	announce_myself();

	my $sigset = POSIX::SigSet->new;
	my $signal = POSIX::SigAction->new(\&sigchld_handler, $sigset, POSIX::SA_NODEFER);
	POSIX::sigaction(POSIX::SIGCHLD, $signal);

	foreach my $worker (1 .. 5) {
		make_child();
	}

	say "[$$] new parent here, looking after children for the rest of my life";

	AnyEvent->condvar->recv;
}

sub announce_myself {
	my $hostname = hostname();

	say "[$$] announcing myself to service discovery";

	# Imagine there's more code here to announce this host with
	# service discovery
}

sub sigchld_handler {
	while (1) {
		my $kid = waitpid(-1, POSIX::WNOHANG);

		if ($kid <= 0) {
			last;
		}

		say "[$$] child $kid died, respawning a new one...";
		make_child();
	}
}

sub make_child {
	my $pid = fork;

	# fork() failed, bail out
	if (not defined $pid) {
		die "fork(): $!";
	}

	if ($pid == 0) {
		# Child proc runs here
		child_main();
		exit(0);
	}
}

sub child_main {
	say "  [$$] child ready, randomly doing stuff";

	while (1) {
		sleep(rand(10));

		# Imagine some real work is being done here, instead of
		# sleeping for random periods of time
	}
}