gistfile1.pl

#!/usr/bin/perl

# Demonstrate handling of waiting for the exit values from multiple
# forked child processes.  Code based on that in the perlipc man page.

use strict;
use warnings;
use feature "say";
use POSIX ":sys_wait_h"; # for waitpid

my $num_procs = 3;
#my $cmd = '/usr/bin/true';
my $cmd = '/usr/bin/false';
my %children;

$SIG{CHLD} = sub {
	local($!, $?);
	my $pid = waitpid(-1, WNOHANG);
	return if $pid == -1;
	return unless defined $children{$pid};
	delete $children{$pid};
	cleanup_child($pid, $?);
};

for (1..$num_procs) {
	my $pid = fork();
	# parent
	if ($pid) {
		say "forked $pid";
		$children{$pid} = 1;
	}
	# child
	else {
		exec $cmd;
	}
}

while (keys %children) {
	my @pids = keys %children;
	my $pids = join ', ', @pids;
	say "waiting for kids: $pids";
	sleep 2;
}

exit;

sub cleanup_child {
	my($pid, $val) = @_;
	say "child $pid had val $val";
}

__END__