#!/usr/bin/perl

use strict;
use warnings;
use threads;
use Thread::Semaphore;

my @files = `ls *.bz2`;
chomp @files;
print "Number of files: ", scalar @files, "\n";

my $count = shift || 20;
print "Number of threads: $count\n";

my @threads;
my $sem = Thread::Semaphore->new ($count);
for (@files)
{
    # request a thread slot, waiting if none are available:
    $sem->down;
    push @threads, async { read_file ($_); };
}
$_->join for @threads;

print "Complete\n";
1;

sub read_file
{
    my $file = shift;
    # что-то сделать с файлом
    ...
    # release slot:
    $sem->up;
}

#!/usr/bin/perl

use strict;
use warnings;
use threads;
use Thread::Queue;

my @files = `ls *.bz2`;
chomp @files;
print "Number of files: ", scalar @files, "\n";

my $count = shift || 20;
print "Number of threads: $count\n";

my $q = Thread::Queue->new;
my @threads;
for (0 .. $count - 1)
{
    push @threads, async {
        while (defined (my $f = $q->dequeue))
        {
            read_file ($f);
        }
    };
}

for (@files)
{
    $q->enqueue ($_);
}

# Tell workers they are no longer needed.
$q->enqueue (undef) for @threads;

# Wait for workers to end
$_->join for @threads;

print "Complete\n";
1;

sub read_file { ... }

#!/usr/bin/perl

use strict;
use warnings;
use Parallel::ForkManager;

my @files = `ls *.bz2`;
die "No *.bz2 files\n" if scalar @files == 0;

my $count = shift || 20;
print "Number of forks: $count\n";

my $pm = Parallel::ForkManager->new ($count);
for my $file (@files)
{
    my $pid = $pm->start and next;
    my $cmd = "perl read_file.pl $file"; # Отдельный скрипт для обработки файла (аналог подпрограммы read_file() в примерах выше)
    exec $cmd or die "Unable to launch '$cmd'\n";
    # Will never reach this, but that's ok since it only calls exit.
    $pm->finish;
}
$pm->wait_all_children;

print "Complete\n";
1;