#! perl -slw
use strict;
use threads;
use threads::shared;

our $T //= 8;

my @buffers; share( $buffers[ $_ ] ) for 0 .. $T-1;
my $stdoutSem :shared;

sub reader {
    my $fname = shift;
    open my $fh, '<', $fname or die $!;

    my $next = 0;
    while( <$fh> ) {
        chomp;
        lock $buffers[ $next ];
        $buffers[ $next ] = $_;
        $next = ++$next % $T;
    }

    close $fh;
    for( 0 .. $T -1 ) {
        lock $buffers[ $_ ];
        $buffers[ $_ ] = undef;
    }
}

sub worker {
    my $tid = threads->tid;
    my $bufn = shift;
    my $localbuf;
    while( 1 ) {
        {
            lock $buffers[ $bufn ];
            last unless defined( $buffers[ $bufn ] );
            $localbuf = $buffers[ $bufn ];
        }
        ## process localbuf here.
        {
            lock $stdoutSem;
            print "[$tid] processed record: '", $localbuf, "'";
        }
    }
}

my $reader = threads->new( \&reader, $ARGV[ 0 ] );
my @workers = map threads->new( \&worker, $_ ), 0 .. $T-1;

$reader->join;

$_->join for @workers;