#! perl -sw
use strict;
use threads;
use Thread::Queue;
use Time::HiRes qw[ time ];

sub worker {
    my $Q = shift;
    while( my $line = $Q->dequeue ) {
         $line =~ s[a][A]g;
         print $line;
    }
}

print "Started " . scalar locatime;
our $T //= 4;
my $n = $T -1;

my @Qs = map Thread::Queue->new, 0 .. $n;

my @threads = map{
    threads->create( \&worker, $Qs[ $_ ] )
} 0 .. $n;

my $start = time;
my $i = 0;
while( <> ) {
    $Qs[ $i ]->enqueue( $_ );
    $i = ( $i + 1 ) % $T;
    warn $., ' ', $. / ( time - $start ) unless $. % 1e6;
}

$Qs[ $_ ]->enqueue( undef ) for 0 .. $n;

$_->join for @threads;

print "Ended " . scalar locatime;