#! perl -slw
use strict;
use threads qw[ yield ];
use threads::shared;
use Thread::Queue;
use Time::HiRes qw[ sleep ];

use constant NTHREADS => 30;

my $pos :shared = 0;

open FILE, '<', $ARGV[ 0 ] or die $!;

my $size = -s FILE;

sub thread {
    my $Q = shift;
    my $tid = threads->tid;
    while( my $line = $Q->dequeue ) {
        printf "%3d: (%10d, %10d) :%s", $tid, $pos, $size, $line;
        sleep rand 5;
    }
}

my $Q = Thread::Queue->new;
my @threads = map threads->create( \&thread, $Q ), 1 .. NTHREADS;

while( !eof FILE ) {
    sleep 0.001 while $Q->pending;
    for( 1 .. NTHREADS ) {
        $Q->enqueue( scalar <FILE> );
        lock $pos;
        $pos = tell FILE;
    }
}

$Q->enqueue( (undef) x NTHREADS );
$_->join for @threads;