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Any::Moose wrapper for queued downloads via Net::Curl & AnyEvent
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AnyEvent::Net::Curl::Queued - Any::Moose wrapper for queued downloads via Net::Curl & AnyEvent


version 0.032


    #!/usr/bin/env perl

    package CrawlApache;
    use feature qw(say);
    use strict;
    use utf8;
    use warnings qw(all);

    use HTML::LinkExtor;
    use Any::Moose;

    extends 'AnyEvent::Net::Curl::Queued::Easy';

    after finish => sub {
        my ($self, $result) = @_;

        say $result . "\t" . $self->final_url;

        if (
            not $self->has_error
            and $self->getinfo('content_type') =~ m{^text/html}
        ) {
            my @links;

            HTML::LinkExtor->new(sub {
                my ($tag, %links) = @_;
                push @links,
                    grep { $_->scheme eq 'http' and $_->host eq 'localhost' }
                    values %links;
            }, $self->final_url)->parse(${$self->data});

            for my $link (@links) {
                $self->queue->prepend(sub {
                    CrawlApache->new({ initial_url => $link });

    no Any::Moose;


    package main;
    use strict;
    use utf8;
    use warnings qw(all);

    use AnyEvent::Net::Curl::Queued;

    my $q = AnyEvent::Net::Curl::Queued->new;
    $q->append(sub {
        CrawlApache->new({ initial_url => 'http://localhost/manual/' })


AnyEvent::Net::Curl::Queued (a.k.a. YADA, Yet Another Download Accelerator) is an efficient and flexible batch downloader with a straight-forward interface capable of:

  • create a queue;
  • append/prepend URLs;
  • wait for downloads to end (retry on errors).

Download init/finish/error handling is defined through Moose's method modifiers.


I am very unhappy with the performance of LWP. It's almost perfect for properly handling HTTP headers, cookies & stuff, but it comes at the cost of speed. While this doesn't matter when you make single downloads, batch downloading becomes a real pain.

When I download large batch of documents, I don't care about cookies or headers, only content and proper redirection matters. And, as it is clearly an I/O bottleneck operation, I want to make as many parallel requests as possible.

So, this is what CPAN offers to fulfill my needs:

AnyEvent::Net::Curl::Queued is a glue module to wrap it all together. It offers no callbacks and (almost) no default handlers. It's up to you to extend the base class AnyEvent::Net::Curl::Queued::Easy so it will actually download something and store it somewhere.


As there's more than one way to do it, I'll list the alternatives which can be used to implement batch downloads:

  • WWW::Mechanize: no (builtin) parallelism, no (builtin) queueing. Slow, but very powerful for site traversal;
  • LWP::UserAgent: no parallelism, no queueing. WWW::Mechanize is built on top of LWP, by the way;
  • LWP::Curl: LWP::UserAgent-alike interface for WWW::Curl. No parallelism, no queueing. Fast and simple to use;
  • HTTP::Tiny: no parallelism, no queueing. Fast and part of CORE since Perl v5.13.9;
  • HTTP::Lite: no parallelism, no queueing. Also fast;
  • Furl: no parallelism, no queueing. Very fast;
  • Mojo::UserAgent: capable of non-blocking parallel requests, no queueing;
  • AnyEvent::Curl::Multi: queued parallel downloads via WWW::Curl. Queues are non-lazy, thus large ones can use many RAM;
  • Parallel::Downloader: queued parallel downloads via AnyEvent::HTTP. Very fast and is pure-Perl (compiling event driver is optional). You only access results when the whole batch is done; so huge batches will require lots of RAM to store contents.


(see also: CPAN modules for making HTTP requests)

Obviously, the bottleneck of any kind of download agent is the connection itself. However, socket handling and header parsing add a lots of overhead.

The script eg/ compares AnyEvent::Net::Curl::Queued against several other download agents. Only AnyEvent::Net::Curl::Queued itself, AnyEvent::Curl::Multi, Parallel::Downloader, Mojo::UserAgent and lftp support parallel connections natively; thus, Parallel::ForkManager is used to reproduce the same behaviour for the remaining agents. Both AnyEvent::Curl::Multi and LWP::Curl are frontends for WWW::Curl. Parallel::Downloader uses AnyEvent::HTTP as it's backend.

The download target is a copy of the Apache documentation on a local Apache server. The test platform configuration:

  • Intel® Core™ i7-2600 CPU @ 3.40GHz with 8 GB RAM;
  • Ubuntu 11.10 (64-bit);
  • Perl v5.16.1 (installed via perlbrew);
  • libcurl 7.27.0 (without AsynchDNS, which slows down curl_easy_init()).

The script eg/ uses Benchmark::Forking and Class::Load to keep UA modules isolated and loaded only once.

    $ perl --count 100 --parallel 4 --repeat 5

                             Request rate WWW::M LWP::UA Mojo::UA HTTP::Tiny HTTP::Lite AE::C::M P::D lftp YADA Furl wget curl LWP::Curl
    WWW::Mechanize v1.72            303/s     --    -65%     -80%       -82%       -85%     -86% -91% -91% -93% -95% -96% -96%      -97%
    LWP::UserAgent v6.04            873/s   187%      --     -44%       -48%       -58%     -60% -74% -74% -79% -87% -89% -89%      -90%
    Mojo::UserAgent v3.39          1558/s   412%     78%       --        -7%       -24%     -29% -54% -54% -63% -76% -80% -80%      -82%
    HTTP::Tiny v0.017              1672/s   451%     92%       8%         --       -19%     -24% -51% -51% -60% -74% -79% -79%      -81%
    HTTP::Lite v2.4                2058/s   577%    136%      32%        23%         --      -6% -39% -39% -51% -68% -74% -74%      -77%
    AnyEvent::Curl::Multi v1.1     2203/s   624%    152%      41%        31%         7%       -- -35% -35% -47% -66% -72% -72%      -75%
    Parallel::Downloader v0.121560 3378/s  1015%    288%     118%       102%        65%      54%   --  -0% -19% -48% -57% -57%      -61%
    lftp v4.3.1                    3401/s  1018%    289%     118%       103%        65%      55%   0%   -- -19% -48% -57% -57%      -61%
    YADA v0.027                    4167/s  1276%    379%     169%       150%       103%      90%  23%  23%   -- -36% -47% -47%      -52%
    Furl v0.40                     6502/s  2041%    645%     318%       288%       216%     196%  92%  91%  56%   -- -17% -18%      -26%
    wget v1.12                     7874/s  2493%    803%     406%       371%       283%     258% 133% 132%  88%  21%   --  -0%      -10%
    curl v7.27.0                   7899/s  2501%    806%     408%       372%       284%     260% 133% 133%  89%  22%   0%   --      -10%
    LWP::Curl v0.12                8757/s  2780%    902%     462%       423%       326%     298% 158% 158% 109%  35%  11%  11%        --

    (output formatted to show module versions at row labels and keep column labels abbreviated)



Allow duplicate requests (default: false). By default, requests to the same URL (more precisely, requests with the same signature are issued only once. To seed POST parameters, you must extend the AnyEvent::Net::Curl::Queued::Easy class. Setting allow_dups to true value disables request checks.


"opts" in AnyEvent::Net::Curl::Queued::Easy attribute common to all workers initialized under the same queue. You may define User-Agent string here.


Count completed requests.


AnyEvent condition variable. Initialized automatically, unless you specify your own. Also reset automatically after "wait", so keep your own reference if you really need it!


Maximum number of parallel connections (default: 4; minimum value: 1).


Net::Curl::Multi instance.


ArrayRef to the queue. Has the following helper methods:


Append item at the end of the queue.


Prepend item at the top of the queue.


Shift item from the top of the queue.


Number of items in queue.


Net::Curl::Share instance.


AnyEvent::Net::Curl::Queued::Stats instance.


Timeout (default: 60 seconds).


Signature cache.


The last resort against the non-deterministic chaos of evil lurking sockets.



Populate empty request slots with workers from the queue.


Check if there are active requests or requests in queue.


Activate a worker.


Put the worker (instance of AnyEvent::Net::Curl::Queued::Easy) at the end of the queue. For lazy initialization, wrap the worker in a sub { ... }, the same way you do with the Moose default => sub { ... }:

    $queue->append(sub {
        AnyEvent::Net::Curl::Queued::Easy->new({ initial_url => 'http://.../' })


Put the worker (instance of AnyEvent::Net::Curl::Queued::Easy) at the beginning of the queue. For lazy initialization, wrap the worker in a sub { ... }, the same way you do with the Moose default => sub { ... }:

    $queue->prepend(sub {
        AnyEvent::Net::Curl::Queued::Easy->new({ initial_url => 'http://.../' })


Process queue.


  • If you mix in fork() calls you may get the "Attempt to free unreferenced scalar: SV 0xdeadbeef during global destruction." message on finalization.
  • Many sources suggest to compile libcurl with c-ares support. This only improves performance if you are supposed to do many DNS resolutions (e.g. access many hosts). If you are fetching many documents from a single server, c-ares initialization will actually slow down the whole process!



Stanislaw Pusep <>


This software is copyright (c) 2012 by Stanislaw Pusep.

This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself.

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