Shell Programming and Scripting

#!/usr/bin/perl
sub spawn {
    $pid = fork;
    unless ($pid) {
        exec "@_";
    }
    $pid
}
@pids = ();
for $i (1..20) {
    $cmd = "sleep $i; echo \$\$";
    $pid = spawn $cmd;
    print "$pid: '$cmd'\n";
    push @pids, $pid;
    if ($i > 10) {
        $pid = shift @pids;
        waitpid $pid, 0;
        printf "Process $pid ended\n";
    }
}
while (@pids) {
    $pid = shift @pids;
    waitpid $pid, 0;
    printf "Process $pid ended\n";
}

#!/bin/bash

N_WORKERS=10
WORK_COUNTER=15
C=$N_WORKERS
PIDS[1]=0
while [ $C != 0 ]; do
        sleep $(($RANDOM / 1000 + 4)) &
        PIDS[$C]=$!
        echo "Sprawned PID: ${PIDS[$C]}"
        WORK_COUNTER=$(($WORK_COUNTER - 1))
        C=$(($C - 1))
done

WORKER_I=$N_WORKERS
WORKERS_RUNNING=$N_WORKERS
while [ $WORKERS_RUNNING != 0 ]; do
        WORKER_I=$(($WORKER_I - 1))
        [ $WORKER_I ==  0 ] && WORKER_I=N_WORKERS
        [ ${PIDS[$WORKER_I]} == 0 ] && continue
        sleep 1

        if [ -z "`ps a | awk '{print $1}' | grep ${PIDS[$WORKER_I]}`" ]; then
                echo "Finished PID: ${PIDS[$WORKER_I]}"

                if [ $WORK_COUNTER != 0 ]; then
                        sleep $(($RANDOM / 1000 + 4)) &
                        PIDS[$WORKER_I]=$!
                        echo "Sprawned PID: ${PIDS[$WORKER_I]}"
                        WORK_COUNTER=$(($WORK_COUNTER - 1))
                else
                        PIDS[$WORKER_I]=0
                        WORKERS_RUNNING=$((WORKERS_RUNNING - 1))
                fi
        fi
done

#!/usr/bin/perl

use POSIX ":sys_wait_h";

%pids = ();
$npids = 0;
$MAX_CHILDREN = 10;

$SIG{CHLD} = \&REAPER;

sub REAPER {
    my $child;
    while (($child = waitpid(-1, WNOHANG)) > 0) {
        # print "$child ($pids{$child}) died!!!\n";
        delete $pids{$child};
        $npids--;
        # print "Child died ($npids still running)\n";
    }
    $SIG{CHLD} = \&REAPER;
}

sub launch {
    my ($cmd) = @_;
    if ($npids >= $MAX_CHILDREN) {
        # print "Zzzz...\n";
        sleep;
    }
    my $pid = fork;
    unless ($pid) {
        exec $cmd;
    }
    $pids{$pid} = $cmd;
    $npids++;
}

sub waitall {
    while ($npids) {
        sleep;
    }
}

for $i (<*.gz>) {
    $cmd = "gzip -d \"$i\"";
    print "Launching $cmd\n";
    launch $cmd;
}

waitall;

if ($npids >= $MAX_CHILDREN) {
        # print "Zzzz...\n";
        sleep;
    }
    my $pid = fork;
    unless ($pid) {