#!/usr/bin/env perl

use warnings;
use strict;

my %cmds;
my ($count, $limit, $actmax) = (0, 10, 2);
my ($cmdline) = 'sleep 1; echo BOOM';
# I think this command will work in Windows but not sure...

sub spawncmd
{
    my ($cmd) = @_;
    my $pid = open(my $of, '-|', $cmd) or die "open: $!";
    ++$count;
    $cmds{$pid} = $of;
    warn "Spawned $pid";
    return $pid;
}

sub cleancmd
{
    my ($pid) = @_;
    die "error: unknown cmd pid: $pid" unless(exists $cmds{$pid});
    my $of = delete $cmds{$pid};
    print "$pid: $_" while(<$of>);
    close($of);
}

spawncmd($cmdline) for(1 .. $actmax);

while(keys(%cmds) > 0){
    my $pid = waitpid(-1, 0);
    die sprintf("error: pid $pid had exit code %d", $? >> 8) if($? != 0);
    cleancmd($pid);
    spawncmd($cmdline) if($count < $limit);
}