IO::Async Paul LeoNerd Evans 2010/12/04 LPW2010 Introductions - - PowerPoint PPT Presentation

IO::Async

Paul “LeoNerd” Evans 2010/12/04 LPW2010

Introductions

• Paul Evans = {

CPAN => “PEVANS”, IRC => “LeoNerd”, }

• A look at the IO::Async distribution

Why Asynchronise?

• IO operations are not instantaneous
• Input comes from a variety of sources at often

unpredictable times

• Blocking operations waste CPU time waiting

when we could be doing other things

• Want to find a way to keep the CPU busy most
• f the time, by waiting on as many things at
• nce as possible

Threads Are Bad

• Can hide many subtle bugs. Bad code can

easily look good

• Humans have a single-threaded thought

process, aren't used to thinking about concurrency

• lets go shopping

Nonblocking Operations

• Do not start an operation if it would block;

EAGAIN

• fcntl(2) to set O_NONBLOCK flag
• Need a way to await operations that can

complete

• select(2), poll(2) (POSIX)
• epoll(4) (Linux), kqueue(2) (BSD), PORTS

(Solaris)

• Notify on ready

Asynchronous Operations

• Perform an operation in the background
• “Nonblocking” connect over TCP – EINPROGRESS
• aio(3) (POSIX)
• IO/CP (MSWin32)
• DNIX
• See also: aio within kqueue, PORTS,...
• Notify on completion

Callbacks and Continuations

• Use a closure as a continuation
• Captures lexical state to resume operation
• Perl has nice support for lexical closures
• See also CPS

IO::Async

• Version: 0.31
• Collection of related modules for asynchronous

IO and related operations

http://search.cpan.org/~pevans/IO-Async-0.31/

IO::Async::Loop

• Single object that performs actual IO

multiplexing operations

• An explicit object, unlike most other eventing

systems

• Performs underlying blocking call (select(2)

et.al.)

• Container for Notifier objects
• “Magic” constructor

Loop Subclasses

• General Purpose
• Select, Poll
• OS specific
• Ppoll, Epoll (Linux)
• KQueue – still under development (BSD)
• Tie into other event systems
• Glib

IO::Async::Notifier

• Base class; subclasses actually perform IO

work

• Notifier alone performs no work, but can act

as a container of others.

• Notifiers form trees, sometimes lone leaves,

all (indirectly) members of a Loop.

IO::Async::Handle

• Contains an IO handle object
• Or two IO handle objects – reading and writing may

be split

• Events on read- or write-readiness
• Usable in two ways:
• Base class – override methods
• Adapter object – provide callback parameters

IO::Async::Stream

• Subclass of Handle
• Wraps a buffer around reading and writing
• on_read designed to avoid common bugs:
• partial records
• multiple records

IO::Async::Timer

• Countdown – fires an event after a fixed delay
• Periodic – fires an event at regular intervals.

Not subject to processing drift

IO::Async::Signal and ::PID

• Multiple Signal objects can watch for one

POSIX signal; no order guarantees

• PID watches for exit of a child process

IO::Async::Protocol + ::Protocol::Stream

• Base-class “abstract” Notifiers
• Perform no IO, delegate such to a Stream
• Allows SSL, SOCKS, etc...
• API looks same as a Stream

IO::Async::Listener

• Wraps a listen-mode socket (usually a TCP

socket)

• Invokes continuation when a new connection is

accept()ed.

• on_accepted, new on_stream / on_socket

Other Notifiers

• DetachedCode – run a blocking call in a child

process, communicate over pipes

• Socket – wrap send/recv queues for

SOCK_DGRAM sockets

• Sequencer – request pipelining, associating

requests with responses

Loop Abilities

• connect and listen
• Nonblocking name and service resolution
• Full IPv6 support
• process management

IO::Async::MergePoint

• Utility object; not a Notifier
• Merge diverged control flow
• Collect information
• Part of the scatter/gather pattern
• See also CPS::kpar

External Distributions

• Generally use Net-Async-* for implementing

networking protocols

• Some distributions take -Async suffix:
• IPC::PerlSSH::Async
• Term::TermKey::Async

IO-Async-SSL

• Extends IO::Async::Loop and related
• Allows connect and listen to use SSL-

wrapped connections in a mostly invisible way

Net-Async-HTTP

• Simple HTTP user agent
• Performs requests against servers
• Body content streaming
• Supports IPv6, SSL

Net-Async-IRC

• Everybody writes one :)
• Just a client connector; no fancy state logic
• Supports IPv6, SSL

Net-Async-FTP

• See also: FtpMustDie
• ... but use it if you must.
• Supports IPv6, SSL

Net-Async-WebSocket

• 0.02 at time of writing – almost entirely untested
• echo-server.pl does work against Chrome
• Supports IPv6, SSL

FCGI-Async

• Original module, before IO::Async existed
• Can respond using
• Custom code
• HTTP::Request / HTTP::Response objects
• PSGI
• Provides Plack::Handler
• Supports IPv6, SSL

Future Directions

• Process Notifier
• Server – subclass of Listener
• Debug support
• Named notifiers
• Event printing
• Aware of notifier nesting, class types
• Intelligence on when / when not to print events

Future Additions

• More Loops
• POE, AnyEvent
• SIGIO
• MSWin32?
• More networking
• IMAP – tm604
• XMPP

Support

• IRC channel
• #ioasync on irc.perl.org

Questions / Comments