#! perl -slw
use strict;
use threads;
use Thread::Queue;

our $BUFSIZE	||= 2**20;

open my $fh, '+< :raw', $ARGV[ 0 ] or die $!;
my $size = -s $fh;

my $Qin = new Thread::Queue;
my $Qout= new Thread::Queue;

async {
	my $buffer;
	while( sysread $fh, $buffer, $BUFSIZE ) {
		$Qin->enqueue( $buffer );
		sleep 1 while $Qin->pending > 10;
	}
	$Qin->enqueue( undef );
}->detach;

my $Tout = async{
	sleep 1 until $Qout->pending;
	sysseek $fh, 0, 0;
	while( my $out = $Qout->dequeue ) {
		syswrite $fh, $out;
	}
};

sleep 1 until $Qin->pending;
while( my $in = $Qin->dequeue ) {
	$in =~ tr[0*][*0];
	$Qout->enqueue( $in );
}
$Qout->enqueue( undef );

$Tout->join;

close $fh;