#!/usr/bin/perl -w

use strict;
use POSIX ":sys_wait_h";

$SIG{CHLD} = sub {wait};

sub logger {

    my $file = shift;
    my $handle;

    open($handle,">$file") || die "in pain: $file: $!";

    select($handle); $| =1; select(STDOUT);

    return sub {

        my $prefix = shift;

        return sub { print $handle "$prefix ".shift()."\n" };
    };
}

# for demo purposes, just to get some overlap

my $warn = logger("warnings");
my $error = logger("errors");

my @identity = qw(identity1 identity2 identity3 identity4);

foreach my $i (1..4) {

    my $identity = shift(@identity);

    unless (my $pid = fork()) {

        my $wlog = &$warn("$identity: ");
        my $elog = &$error("$identity: ");

        # make things a little more tidy

        sub logwarn { &$wlog(shift); }
        sub logerror { &$elog(shift); }

        foreach my $t (1..3) {

            sleep 2;

            logwarn("random warning $t");
            logerror("random error $t");
        }

        exit(0);
    }

    sleep(2);
}

my $kid;

do {

    $kid = waitpid(-1,&WNOHANG);

} until $kid == -1;