IO::Async(3) User Contributed Perl Documentation IO::Async(3)NAME
"IO::Async" - Asynchronous event-driven programming
SYNOPSIS
use IO::Async::Stream;
use IO::Async::Loop;
my $loop = IO::Async::Loop->new;
$loop->connect(
host => "some.other.host",
service => 12345,
socktype => 'stream',
on_stream => sub {
my ( $stream ) = @_;
$stream->configure(
on_read => sub {
my ( $self, $buffref, $eof ) = @_;
while( $$buffref =~ s/^(.*\n)// ) {
print "Received a line $1";
}
return 0;
}
);
$stream->write( "An initial line here\n" );
$loop->add( $stream );
},
on_resolve_error => sub { die "Cannot resolve - $_[-1]\n"; },
on_connect_error => sub { die "Cannot connect - $_[0] failed $_[-1]\n"; },
);
$loop->run;
DESCRIPTION
This collection of modules allows programs to be written that perform
asynchronous filehandle IO operations. A typical program using them
would consist of a single subclass of IO::Async::Loop to act as a
container of other objects, which perform the actual IO work required
by the program. As well as IO handles, the loop also supports timers
and signal handlers, and includes more higher-level functionality built
on top of these basic parts.
Because there are a lot of classes in this collection, the following
overview gives a brief description of each.
Notifiers
The base class of all the event handling subclasses is
IO::Async::Notifier. It does not perform any IO operations itself, but
instead acts as a base class to build the specific IO functionality
upon. It can also coordinate a collection of other Notifiers contained
within it, forming a tree structure.
The following sections describe particular types of Notifier.
File Handle IO
An IO::Async::Handle object is a Notifier that represents a single IO
handle being managed. While in most cases it will represent a single
filehandle, such as a socket (for example, an IO::Socket::INET
connection), it is possible to have separate reading and writing
handles (most likely for a program's "STDIN" and "STDOUT" streams, or a
pair of pipes connected to a child process).
The IO::Async::Stream class is a subclass of IO::Async::Handle which
maintains internal incoming and outgoing data buffers. In this way, it
implements bidirectional buffering of a byte stream, such as a TCP
socket. The class automatically handles reading of incoming data into
the incoming buffer, and writing of the outgoing buffer. Methods or
callbacks are used to inform when new incoming data is available, or
when the outgoing buffer is empty.
While stream-based sockets can be handled using using
"IO::Async::Stream", datagram or raw sockets do not provide a
bytestream. For these, the IO::Async::Socket class is another subclass
of IO::Async::Handle which maintains an outgoing packet queue, and
informs of packet receipt using a callback or method.
The IO::Async::Listener class is another subclass of IO::Async::Handle
which facilitates the use of listen(2)-mode sockets. When a new
connection is available on the socket it will accept(2) it and pass the
new client socket to its callback function.
Timers
An IO::Async::Timer::Absolute object represents a timer that expires at
a given absolute time in the future.
An IO::Async::Timer::Countdown object represents a count time timer,
which will invoke a callback after a given delay. It can be stopped and
restarted.
An IO::Async::Timer::Periodic object invokes a callback at regular
intervals from its initial start time. It is reliable and will not
drift due to the time taken to run the callback.
The IO::Async::Loop also supports methods for managing timed events on
a lower level. Events may be absolute, or relative in time to the time
they are installed.
Signals
An IO::Async::Signal object represents a POSIX signal, which will
invoke a callback when the given signal is received by the process.
Multiple objects watching the same signal can be used; they will all
invoke in no particular order.
Processes Management
An IO::Async::PID object invokes its event when a given child process
exits. An IO::Async::Process object can start a new child process
running either a given block of code, or executing a given command, set
up pipes on its filehandles, write to or read from these pipes, and
invoke its event when the child process exits.
Loops
The IO::Async::Loop object class represents an abstract collection of
IO::Async::Notifier objects, and manages the actual filehandle IO
watchers, timers, signal handlers, and other functionality. It performs
all of the abstract collection management tasks, and leaves the actual
OS interactions to a particular subclass for the purpose.
IO::Async::Loop::Poll uses an IO::Poll object for this test.
IO::Async::Loop::Select uses the select(2) syscall.
Other subclasses of loop may appear on CPAN under their own dists; see
the "SEE ALSO" section below for more detail.
As well as these general-purpose classes, the IO::Async::Loop
constructor also supports looking for OS-specific subclasses, in case a
more efficient implementation exists for the specific OS it runs on.
Child Processes
The IO::Async::Loop object provides a number of methods to facilitate
the running of child processes. "spawn_child" is primarily a wrapper
around the typical fork(2)/exec(2) style of starting child processes,
and "run_child" provide a method similar to perl's "readpipe" (which is
used to implement backticks "``").
File Change Watches
The IO::Async::File object observes changes to stat(2) properties of a
file, directory, or other filesystem object. It invokes callbacks when
properties change. This is used by IO::Async::FileStream which presents
the same events as a "IO::Async::Stream" but operates on a regular file
on the filesystem, observing it for updates.
Asynchronous Co-routines and Functions
The "IO::Async" framework generally provides mechanisms for
multiplexing IO tasks between different handles, so there aren't many
occasions when it is necessary to run code in another thread or
process. Two cases where this does become useful are when:
· A large amount of computationally-intensive work needs to be
performed.
· An OS or library-level function needs to be called, that will
block, and no asynchronous version is supplied.
For these cases, an instance of IO::Async::Function can be used around
a code block, to execute it in a worker child process or set of
processes. The code in the sub-process runs isolated from the main
program, communicating only by function call arguments and return
values. This can be used to solve problems involving state-less library
functions.
An IO::Async::Routine object wraps a code block running in a separate
process to form a kind of co-routine. Communication with it happens via
IO::Async::Channel objects. It can be used to solve any sort of problem
involving keeping a possibly-stateful co-routine running alongside the
rest of an asynchronous program.
Futures
An IO::Async::Future object represents a single outstanding action that
is yet to complete, such as a name resolution operation or a socket
connection. It stands in contrast to a "IO::Async::Notifier", which is
an object that represents an ongoing source of activity, such as a
readable filehandle of bytes or a POSIX signal.
Futures are a recent addition to the "IO::Async" API and details are
still subject to change and experimentation.
In general, methods that support Futures return a new Future object to
represent the outstanding operation. If callback functions are supplied
as well, these will be fired in addition to the Future object becoming
ready. Any failures that are reported will, in general, use the same
conventions for the Future's "fail" arguments to relate it to the
legacy "on_error"-style callbacks.
$on_NAME_error->( $message, @argmuents )
$f->fail( $message, NAME, @arguments )
where $message is a message intended for humans to read (so that this
is the message displayed by "$f->get" if the failure is not otherwise
caught), "NAME" is the name of the failing operation. If the failure is
due to a failed system call, the value of $! will be the final
argument. The message should not end with a linefeed.
Networking
The IO::Async::Loop provides several methods for performing network-
based tasks. Primarily, the "connect" and "listen" methods allow the
creation of client or server network sockets. Additionally, the
"resolve" method allows the use of the system's name resolvers in an
asynchronous way, to resolve names into addresses, or vice versa. These
methods are fully IPv6-capable if the underlying operating system is.
Protocols
The IO::Async::Protocol class provides storage for a IO::Async::Handle
object, to act as a transport for some protocol. It allows a level of
independence from the actual transport being for that protocol,
allowing it to be easily reused. The IO::Async::Protocol::Stream
subclass provides further support for protocols based on stream
connections, such as TCP sockets.
TODO
This collection of modules is still very much in development. As a
result, some of the potentially-useful parts or features currently
missing are:
· Consider further ideas on Solaris' ports, BSD's Kevents and
anything that might be useful on Win32.
· Consider some form of persistent object wrapper in the form of an
"IO::Async::Object", based on "IO::Async::Routine".
· "IO::Async::Protocol::Datagram"
· Support for watching filesystem entries for change. Extract logic
from "IO::Async::File" and define a Loop watch/unwatch method pair.
· Define more "Future"-returning methods. Consider also one-shot
Futures on things like "IO::Async::Process" exits, or
"IO::Async::Handle" close.
SUPPORT
Bugs may be reported via RT at
https://rt.cpan.org/Public/Dist/Display.html?Name=IO-Async
Support by IRC may also be found on irc.perl.org in the #io-async
channel.
SEE ALSO
As well as the two loops supplied in this distribution, many more exist
on CPAN. At the time of writing this includes:
· IO::Async::Loop::AnyEvent - use IO::Async with AnyEvent
· IO::Async::Loop::Epoll - use IO::Async with epoll on Linux
· IO::Async::Loop::Event - use IO::Async with Event
· IO::Async::Loop::EV - use IO::Async with EV
· IO::Async::Loop::Glib - use IO::Async with Glib or GTK
· IO::Async::Loop::KQueue - use IO::Async with kqueue
· IO::Async::Loop::Mojo - use IO::Async with Mojolicious
· IO::Async::Loop::POE - use IO::Async with POE
· IO::Async::Loop::Ppoll - use IO::Async with ppoll(2)
Additionally, some other event loops or modules also support being run
on top of "IO::Async":
· AnyEvent::Impl::IOAsync - AnyEvent adapter for IO::Async
· Gungho::Engine::IO::Async - IO::Async Engine
· POE::Loop::IO_Async - IO::Async event loop support for POE
AUTHOR
Paul Evans <leonerd@leonerd.org.uk>
perl v5.18.2 2014-05-14 IO::Async(3)
