Asynchronous Event
programming with AnyEvent
Tatsuhiko Miyagawa
YAPC::Asia 2009

Questions:
Are you familiar with
Event loops?

Questions:
Have you used POE?

Intro
Basics
Examples
Tips

AnyEvent
Intro

“DBI of event loops”

(Used in Remedie!)

Event loops on CPAN

POE IO::Async
Danga::Socket
IO::Lambda
Event Event::Lib
EV Glib Qt Tk ...

Incompatible APIs

Different Styles

#!/usr/bin/perl
use POE;
POE::Session->create(
inline_states => {
_start => sub {
$_[HEAP]->{count} = 0;
$_[KERNEL]->yield(‘incr’);
},
incr => sub {
warn $_[HEAP]->{count}++;
$_[KERNEL]->yield(‘incr’);
},
}
);
POE::Kernel->run

use IO::Async::Loop;
use IO::Async::Stream;
use Socket qw( SOCK_STREAM );
my $loop = IO::Async::Loop->new;
$loop->connect(
host => “example.com”,
service => 80,
socktype => SOCK_STREAM,
on_connected => sub {
my $socket = shift;
...
}
);
$loop->loop_forever;

More important:

CPAN Modules

250

POE::Components
on CPAN

POE::Component::*
don’t work with
IO::Async etc.

AnyEvent::Impl::*

AnyEvent code can
work under
“Any Event” loops

#!/usr/bin/perl
use POE;
use AnyEvent;
POE::Session->create(
inline_states => {
...
}
);
my $w = AnyEvent->timer(
after => 0,
cb => sub { ... }
);
POE::Kernel->run; # Just works

AnyEvent modules:
35

CPAN authors:
Stop writing PoCos :)

Intro
Basics
Examples
Tips

#!/usr/bin/perl
use AnyEvent;
my $i;
my $cv = AnyEvent->condvar;
my $w = AnyEvent->timer(
after => 0, interval => 1,
cb => sub {
warn “checking “, $i++;
$cv->send() if $i > 10;
}
);
$cv->recv;

Timer Watcher
condvar
I/O
subprocess
modules

my $t1 = AnyEvent->timer(
after => 0,
cb => sub {
# ...
}
);
my $t2 = AnyEvent->timer(
after => 0,
interval => 3,
cb => sub {
# ...
}
);

my $cv = AnyEvent->condvar;
my $w = AnyEvent->timer(
after => 5,
cb => sub {
$cv->send(“DONE”);
},
);
my $r = $cv->recv; # $r = ‘DONE’

my $io = AnyEvent->io(
fh => *STDIN,
poll => ‘r’,
cb => sub {
# $fh is ready to read
my $line = <$fh>; # scalar!
}
);

use AnyEvent::Handle;
my $hd; $hd = AnyEvent::Handle->new(
fh => $fh,
);
$hd->push_read(line => sub {
my($hd, $line) = @_;
});
$hd->push_read(chunk => 8, sub {
my($hd, $bytes) = @_;
});
$hd->push_read(json => sub {
my($hd, $obj) = @_;
});

use AnyEvent::Socket;
tcp_connect $host, $port, sub {
my $fh = shift or die “FAIL”;
my $hd = AnyEvent::Handle->new(
fh => $fh,
);
$hd->push_read(json => sub {
my($hd2, $obj) = @_;
});
};

use AnyEvent::HTTP;
http_get “http://google.com/”, sub {
my($body, $header) = @_;
# $header->{Status};
# $header->{‘content-type’};
};

Intro
Basics
Examples
Tips

AnyEvent::Twitter::Stream

Twitter Streaming API
aka Firehose

use AnyEvent::Twitter::Stream;
my $cv = AnyEvent->condvar;
my $s = AnyEvent::Twitter::Stream->new(
username => $user,
password => $pass,
method => ‘filter’,
track => ‘#yapc,#yapcasia2009’,
on_tweet => sub {
my $tweet = shift;
printf “%s:%sn”,
$tweet->{user}{screen_name},
$tweet->{text};
},
on_eof => $cv,
);
$cv->recv;

AnyEvent::ReverseHTTP

client becomes server
server becomes client

Polling HTTP GET
with AnyEvent::HTTP

use AnyEvent::ReverseHTTP;
my $guard = reverse_http
$hostname, $token, sub {
my $req = shift;
return “Hello World”;
};
AnyEvent->condvar->recv;

Intro
Basics
Examples
Tips

Condvars

Transactions
(multi signals)

Parallel downloads
with AnyEvent::HTTP

use AnyEvent::HTTP;
my $cv = AnyEvent->condvar;
for my $i (1..3) {
$cv->begin;
http_get "http://search.cpan.org/
search?q=$i", sub {
my $body = shift;
warn length $body;
$cv->end;
};
}
$cv->recv;

Scope of watchers

for (1..10) {
my $w = AnyEvent->timer(
after => 1,
cb => sub { ... }
);
}
AnyEvent->condvar->recv;

for (1..10) {
my $w = AnyEvent->timer(
after => 1,
cb => sub { ... }
);
# $w goes out of scope!
}
AnyEvent->condvar->recv;

for (1..10) {
my $w; $w = AnyEvent->timer(
after => 1,
cb => sub {
...
undef $w;
}
);
}
AnyEvent->condvar->recv;

multiple condvars
waiting

You can’t call ->recv
on multiple $cv

USe $cv->cb() instead

for (1..10) {
my $cv = AnyEvent->condvar;
my $w; $w = AnyEvent->timer(
after => 1,
cb => sub { $w; $cv->send },
);
$cv->recv; # blocks
}

for (1..10) {
my $cv = AnyEvent->condvar;
my $w; $w = AnyEvent->timer(
after => 1,
cb => sub { $w; $cv->send($v) },
);
$cv->cb(sub {
my $v = $cv->recv;
...
});
}

Or:
use Coro::AnyEvent

CPAN authors:

Write a simple
callback API

use AnyEvent::mDNS;
my $cv = AnyEvent->condvar;
# $cv can be called as a callbak
my $g = AnyEvent::mDNS::discover
‘_daap._tcp’, $cv;
my @itunes = $cv->recv;

Use guard { }
to cleanup

use AnyEvent::ReverseHTTP;
{
my $guard = reverse_http $h, $t,
sub {
my $req = shift;
};
# ...
}

Beware of
circular references
(Scalar::Util::weaken)

API to pass/return
condvar for better
control by users

use AnyEvent::ReverseHTTP;
my $guard = reverse_http $h, $t,
sub {
my $req = shift;
my $cv = AnyEvent->condvar;
my $t; $t = AnyEvent->timer(
after => 5,
cb => sub {
my $res = HTTP::Response->new;
undef $t;
$cv->send($res);
}
};
return $cv;
};

New AE API

use AnyEvent;
my $t = AE::timer 0, 1, $cb;
my $w = AE::io $fh, $write, $cb;
my $cv = AE::cv;

Summary

AnyEvent
Very useful
Nice utilities
No bloated POE stuff

Questions?

Thank you.