#perl

use AnyEvent;

my $input_waiting = AnyEvent->condvar;
my $output_waiting = AnyEvent->condvar;

my $input_from_stdin = AnyEvent->io (
	fh   => \*STDIN, # which file handle to check
	poll => "r",     # which event to wait for ("r"ead data)
	cb   => sub {    # what callback to execute
		my $input = <STDIN>; # read it
		push(@input, $input);
		$input_waiting->send;

		$output_waiting->recv;
		print shift(@output) ."\n";
	}
);


while(1){
	# this "blocks" (while handling events) till the callback
	# calls ->send
	$input_waiting->recv;

	## do some possibly lengthy processing
	push(@output, 'done');
	$output_waiting->send;

	## finish this cycle,
	## AnyEvent docs say: "You can only wait once on a condition - additional calls are valid but will return immediately."
	## but we need to stop this loop again, so this:
	$input_waiting = AnyEvent->condvar;
}