NAME

Object::RateLimiter - A flood control (rate limiter) object

SYNOPSIS

  use Object::RateLimiter;

  my $ctrl = Object::RateLimiter->new(
    events  => 3,
    seconds => 5
  );

  # Run some subs, as a contrived example;
  # no more than 3 in 5 seconds, per our constructor above:
  my @work = (
    sub { "foo" },  sub { "bar" },
    sub { "baz" },  sub { "cake" },
    # ...
  );

  while (my $some_item = shift @work) {
    if (my $delay = $ctrl->delay) {
      # Delayed $delay (fractional) seconds.
      # (You might want Time::HiRes::sleep, or yield to event loop, etc)
      sleep $delay;
    } else {
      # No delay.
      print $some_item->()
    }
  }

  # Clear the event history if it's stale:
  $ctrl->expire;

  # Clear the event history unconditionally:
  $ctrl->clear;

DESCRIPTION

This is a generic rate-limiter object, implementing the math described in http://www.perl.com/pub/2004/11/11/floodcontrol.html via light-weight array-type objects.

The algorithm is fairly simple; the article linked above contains an in-depth discussion by Vladi Belperchinov-Shabanski (CPAN: http://www.metacpan.org/author/CADE):

  $delay =
    ( 
      $oldest_timestamp + 
      ( $seen_events * $limit_secs / $event_limit ) 
    )
    - time()

This module uses Time::HiRes to provide support for fractional seconds.

new

  my $ctrl = Object::RateLimiter->new(
    events  => 3,
    seconds => 5
  );

Constructs a new rate-limiter with a clean event history.

clear

  $ctrl->clear;

Clears the event history. Always returns true.

clone

  my $new_ctrl = $ctrl->clone( events => 4 );

Clones an existing rate-limiter; new options can be provided, overriding previous settings.

The new limiter contains a clone of the event history; the old rate-limiter is left untouched.

delay

  if (my $delay = $ctrl->delay) {
    sleep $delay;  # ... or do something else
  } else {
    # Not delayed.
    do_work;
  }

The delay() method determines if some work can be done now, or should wait.

When called, event timestamps are considered; if we have exceeded our limit, the delay in (possibly fractional) seconds until the event would be allowed is returned.

A return value of 0 indicates that the event does not need to wait.

events

Returns the events limit the object was constructed with.

expire

  $ctrl->expire;

Clears the event history if "is_expired" is true.

Returns true if "clear" was called.

You're not required to call expire(), but it can be useful to save a little memory (a 10 event history uses about 1kb here).

is_expired

Returns true if the last seen event is outside of our time window (in other words, the event history is stale) or there is no event history.

Also see "expire"

seconds

Returns the seconds limit the object was constructed with.

AUTHOR

Jon Portnoy <avenj@cobaltirc.org>

Based on the math from Algorithm::FloodControl as described in an article written by the author: http://www.perl.com/pub/2004/11/11/floodcontrol.html

Licensed under the same terms as Perl.