Question

I’m using an Event var watcher to implement an internal queue. When the producer thread adds something to the queue (just an array) it will change the value of a watched variable to signal that an element was added.

How can you do the same with AnyEvent? It doesn’t seem to support variable watching. Do I have to use pipes and use an IO watcher (i.e. the producer writes a byte on one end of the pipe when it has added an element.)

I’d also be interested to know how to do this with Coro.

Answer 1

I figured out the paradigm to use:

my @queue;
my $queue_watcher;

sub add_item {
   push(@queue, $_[0]);
   $queue_watcher ||= AnyEvent->timer(after => 0, cb => \&process_queue);
}

sub process_queue {
  ... # remove zero or more elements from @queue
  if (@queue) {
    $queue_watcher = AnyEvent->timer(after => 0, cb => \&process_queue);
  } else {
    undef $queue_watcher;
  }
}

Basically $queue_watcher is defined and active if and only if @queue is not empty.