use strict;
use warnings;
require POSIX;	# provides WNOHANG

# Set up a signal handler.
# This prevents child processes from becoming zombies.
# The subroutine is defined further below.

$SIG{CHLD} = \&reap_kids;

# Track spawned child processes.
# This is a hash, keyed by the PID.
# We'll use this later to mark them as finished.
my %kids;

for my $child_id (1..3) {
	my $pid = fork();

	# PARENT: track kid
	if ($pid) {
		$kids{$pid} = 1;
	}
	# CHILD: dispatch to child-routine below.
	# Explicitly exit, in case the child code neglects.
	else {
		dispatch_child( $child_id );
		exit(0);
	}
}

print "Main code now waiting for all children.\n";

# Wait for all children to finish.
# The signal handler, reap_kids(), catches finished children.
# Just continue to sleep if there are pending processes.
while( scalar(keys %kids) > 0 ) {
	sleep 1;
}

# That's all the main code does.
print "All done with main code.\n";
exit(0);

# ---
# Suborutines 
# ---

# Child reaper.
# This will be called when the kernel tells us a process has
# finished running. It's possible more than 1 has done so.
# We run this in a loop to reap all children.
sub reap_kids {
	local $!; # good practice. avoids changing errno.
	while (1) {
		my $kid = waitpid( -1, POSIX->WNOHANG );
		last unless ($kid > 0); # No more to reap.
		delete $kids{$kid}; # untrack kid.
	}
}

# Child dispatch code.
# Here is where you write what your child does.
# Ideally it should exit, but we enforce this above anyway.
sub dispatch_child {
	my $id = shift; # passed from caller.

	print "Hello from child number $id\n";

	# Sleep for a random number of seconds.
	# Between 5 and 10.
	my $seconds = 5 + int(rand(6));
	sleep $seconds;

	print "Goodbye from child number $id\n";
	
	# Be nice and explicitly exit:
	exit(0);
}