Dotan Dimet דותן דימט
and 3 contributors

NAME

Mojo::UserAgent::Role::Queued - A role to process non-blocking requests in a rate-limiting queue.

SYNOPSIS

    use Mojo::UserAgent;

    my $ua = Mojo::UserAgent->new->with_roles('+Queued');
    $ua->max_redirects(3);
    $ua->max_active(5); # process up to 5 requests at a time
    for my $url (@big_list_of_urls) {
    $ua->get($url, sub {
            my ($ua, $tx) = @_;
            if ($tx->success) {
                say "Page at $url is titled: ",
                  $tx->res->dom->at('title')->text;
            }
           });
   };
   # works with promises, too:
  my @p = map {
    $ua->get_p($_)->then(sub { pop->res->dom->at('title')->text })
      ->catch(sub { say "Error: ", @_ })
  } @big_list_of_urls;
   Mojo::Promise->all(@p)->wait;
 

DESCRIPTION

Mojo::UserAgent::Role::Queued manages all non-blocking requests made through Mojo::UserAgent in a queue to limit the number of simultaneous requests.

Mojo::UserAgent can make multiple concurrent non-blocking HTTP requests using Mojo's event loop, but because there is only a single process handling all of them, you must take care to limit the number of simultaneous requests you make.

Some discussion of this issue is available here http://blogs.perl.org/users/stas/2013/01/web-scraping-with-modern-perl-part-1.html and in Joel Berger's answer here: http://stackoverflow.com/questions/15152633/perl-mojo-and-json-for-simultaneous-requests.

Mojo::UserAgent::Role::Queued tries to generalize the practice of managing a large number of requests using a queue, by embedding the queue inside Mojo::UserAgent itself.

EVENTS

Mojo::UserAgent::Role::Queued adds the following event to those emitted by Mojo::UserAgent:

queue_empty

  $ua->on(queue_empty => sub { my ($ua) = @_; .... })

Emitted when the queue has been emptied of all pending jobs. In previous releases, this event was called stop_queue (this is a breaking change).

ATTRIBUTES

Mojo::UserAgent::Role::Queued has the following attributes:

max_active

    $ua->max_active(5);  # execute no more than 5 transactions at a time.
    print "Execute no more than ", $ua->max_active, " concurrent transactions"

Parameter controlling the maximum number of transactions that can be active at the same time.

LICENSE

Copyright (C) Dotan Dimet.

This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself.

AUTHOR

Dotan Dimet <dotan@corky.net>