while( @jobq ) {
    if ( $counter < $num_children ) {
        &SPAWN( $ref );
    }
    else {
        do {
           sleep 5;
           $dpid = waitpid( -1, 1 );
        } until $dpid;
        last if ( $dpid == -1 );  # No children left
        printf "%s has finished, spawning next child (%d left)\n", $tracker{$dpi
d}, scalar @jobq;
        &SPAWN( $ref );
    }
}

do {
    sleep 5;
    $dpid = waitpid( -1, 1 );
    printf("%s has finished\n", $tracker{$dpid}) if(defined( $tracker{$dpid} )
    );
} until $dpid == -1;