IO::Event(3pm) User Contributed Perl Documentation IO::Event(3pm)

IO::Event - Tied Filehandles for Nonblocking IO with Object Callbacks

 use IO::Event;
 use IO::Event 'emulate_Event';
 use IO::Event 'AnyEvent';
 my $ioe = IO::Event->new($filehandle);
 my $ioe = IO::Event::Socket::INET->new( [ARGS] )
 my $ioe = IO::Event::Socket::UNIX->new( [ARGS] )
 my $timer = IO::Event->timer(
        [after => $seconds],
        interval => $seconds,
        cb => CODE);
 my $idler = IO::Event->idle(
        [min => $seconds], 
        [max => $seconds],
        [reentrant => 0],
        cb => CODE);
 IO::Event::loop();
 IO::Event::unloop_all();

IO::Event provides a object-based callback system for handling nonblocking IO. The design goal is to provide a system that just does the right thing w/o the user needing to think about it much.

All APIs are kept as simple as possible yet at the same time, all functionality is accesible if needed. Simple things are easy. Hard things are possible.

Most of the time file handling syntax will work fine: "<$filehandle>" and "print $filehandle 'stuff'".

IO::Event provides automatic buffering of output (with a callback to throttle). It provides automatic line-at-a-time input.

After initial setup, call "IO::Event::loop()".

IO::Event was originally written to use Event. IO::Event still defaults to using Event but it can now use AnyEvent or its own event loop.

Until you create your first IO::Event object, you can choose which underlying event handler to use. The default is Event. To choose an event handler, use one of the following lines, import "no_emulate_Event", "emulate_Event", or "AnyEvent".

 use IO::Event 'no_emulate_Event'
 use IO::Event 'emulate_Event'
 use IO::Event 'AnyEvent'

The "no_emulate_Event" option means: use Event. The "emulate_Event" option means IO::Event should use its own event loop.

Why?

You should use AnyEvent if you want to have compatibility with other event loops. You should use "emulate_Event" if you don't need compatibility with other event loops and you have missing-event bugs when using Event. You should use Event if it works for you.

The APIs are a bit different depending on which event loop you're using.

To use Event's event loop:

 use IO::Event 'no_emulate_Event';

or just:

 use IO::Event

IO::Event's definition for "loop()", "timer()", "idle()" and "unloop_all()" all default to the Event version unless "emulate_Event" or "AnyEvent" have been imported. This allows you to easily switch back and forth between Event's API and the others.

To use AnyEvent's select loop, import "AnyEvent".

 use IO::Event 'AnyEvent';

You can use AnyEvent's API directly or you can use IO::Event's emulated APIs: "IO::Event::loop()", "IO::Event::unloop()", "IO::Event::timer()", and "IO::Event::idle()". These behave like Event's routines of the same name but use AnyEvent underneath.

During testing, using the pure-perl event loop of AnyEvent::Impl::Perl from AnyEvent version 5.271, some read events were dropped. To work around this, a synthetic read-ready event is dispatched for all connected read filehandles every two seconds. Turn this off or adjust its frequency by changing $IO::Event::AnyEvent::lost_event_hack. A numeric value is the time (in seconds) between dispatching read events. A false value turns off this performance-sapping hack.

AnyEvent only provides basic support for idle() events: it promises to invoke them "every now and then".

To use IO::Event's own select loop, import "emulate_Event".

 use IO::Event 'emulate_Event';

IO::Event does not provide a complete emulation of everything that Event does. It provides the full timer API:

 my $timer = IO::Event::timer( [ARGS] )

instead of

 my $timer = Event::timer( [ARGS] )

However it does not provide timer events on filehandles, nor does it provide events for signals, or variable accesses.

Use "IO::Event::loop()" instead of "Event::loop()". Use "IO::Event::unloop_all()" instead of "Event::unloop_all()". Use "IO::Event::idle()" instead of "Event::idle()". It does not provide any other methods or functions from Event. If you need them, please send a patch.

The basic "new" constructor takes a filehandle and returns a psuedo-filehandle. Treat the IO::Event object as a filehandle. Do not use the original filehandle without good reason (let us know if you find a good reason so we can fix the problem).

The handler is the class or object where you provide callback functions to handle IO events. It defaults to the package of the calling context.

If present, $options is a hash reference with the following possible keys:

A text description of this filehandle. Used for debugging and error messages.
Set to true if this is a read-only filehandle. Do not accept output.
Set to true if this is a write-only filehandle. Do not attept to read.
Set to 0 if this should not be an auto-read filehandle.
This constructor uses IO::Socket::INET->new() to create a socket using the ARGS provided. It returns an IO::Event object.

The handler defaults as above or can be set with an additional pseudo-parameter for IO::Socket::UNIX->new(): "Handler". A description for the socket can be provided with an additional psuedo-parameter: "Description".

This constructor uses IO::Socket::UNIX->new() to create a socket using the ARGS provided. It returns an IO::Event object.

The handler defaults as above or can be set with an additional pseudo-parameter for IO::Socket::UNIX->new(): "Handler". A description for the socket can be provided with an additional psuedo-parameter: "Description".

These handler methods must be available in the handler object/class if the situation in which they would be called arises.

Invoked when there is fresh data in the input buffer. The input can be retrieved via directly reading it from $$input_buffer_reference or via "read()" from the $ioe filehandle, or by using a variety of standard methods for getting data: 

        <$ioe>                  like IO::Handle
        $ioe->get()             like Data::LineBuffer
        $ioe->read()            like IO::Handle
        $ioe->sysread()         like IO::Handle
        $ioe->getline()         like IO::Handle
        $ioe->getlines()        like IO::Handle
        $ioe->getsome()         see below
        $ioe->ungets()          like FileHandle::Unget

At end-of-file, ie_input will only be invoked once. There may or may not be data in the input buffer.

Invoked when a listen()ing socket is ready to accept(). It should call accept: 

        sub ie_connection
        {
                my ($pkg, $ioe) = @_;
                my $newfh = $ioe->accept()
        }
If autoreading is turned off then this will be invoked.
A write error has occured when trying to drain the write buffer. Provide an empty subroutine if you don't care.

These handler methods will be called if they are defined but it is not required that they be defined.

This is invoked when the read-side of the filehandle has been closed by its source.
This is invoked when data has just been written to the underlying filehandle.
This is invoked when all pending data has just been written to the underlying filehandle.
This is invoked when a "connect()" completes.
This is invoked when a "connect()" fails. For a timeout, the error code will be ETIMEOUT.
If another handler calls "die" then ie_died will be called with the IO::Event object, the name of the method just invoked, and the die string. If no ie_died() callback exists then execution will terminate.
This is invoked for timer events.
Invoked when an exceptional condition arises on the underlying filehandle
Invoked when there is too much output data and the output buffers are overflowing. You can take some action to generate less output. This will be invoked exactly once (with $overflowing == 1) when there is too much data in the buffer and then exactly once again (with $overflowing == 0) when there is no longer too much data in the buffer.

In addition to methods described in detail below, the following methods behave like their "IO" (mostly "IO::Socket") counterparts (except for being mostly non-blocking...):

        connect
        listen
        open
        read
        sysread
        syswrite
        print
        eof
        shutdown

Through AUTOLOAD (see the SUBSTITUTED METHODS section) methods are passed to underlying "Event" objects:

        loop
        unloop
        and many more...

Through AUTOLOAD (see the SUBSTITUTED METHODS section) methods are passed to underlying "IO" objects:

        fileno
        stat
        truncate
        error
        opened
        untaint
        and many more...

IO::Event defines its own methods too:

->accept($handler, %options)
accept() is nearly identical to the normal IO::Socket::accept() method except that instead of optionally passing a class specifier for the new socket, you optionally pass a handler object or class. The returned filehandle is an IO::Event object.

Supported options:

Sets the description for the new socket
Set to 0 if you do not want auto-read
->can_read($amount)
Returns true if $amount bytes worth of input is available for reading. Note: this does not return true at EOF so be careful not to hang forever at EOF.
->getsome($amount)
Returns $amount bytes worth of input or undef if the request can't be filled. Returns what it can at EOF.
->get()
get() is like getline() except that it pre-chomp()s the results and assumes the input_record_separator is "\n". This is like get() from Data::LineBuffer.
->unget()
Push chomp()ed lines back into the input buffer. This is like unget() from Data::LineBuffer.
->ungetline(), ->xungetc(), ->ungets()
This is what ungetc() should be: it pushes a string back into the input buffer. This is unlike IO::Handle->ungetc which takes an ordinal and pushes one character back into the the input buffer. This is like FileHandle::Unget.
->handler($new_handler)
Sets the handler object/class if $new_handler is provided. Returns the old handler.
->filehandle()
Returns the underlying "IO::Handle".
->event()
Returns the underling "Event".
->listener($listening)
Used to note that a filehandle is being used to listen for connections (instead of receiving data). A passed parameter of 0 does the opposite. Returns the old value. This is mostly used internally in IO::Event.
->input_record_separator($new_sep)
IO::Handle doesn't allow input_record_separator's on a per filehandle basis. IO::Event does. If you don't ever set a filehandle's input record separator, then it contineously defaults to the current value of $/. If you set it, then it will use your value and never look at $/ again.
->readevents($readevents)
Get/set listening for read-ready events on the underlying filehandle. This could be used by ie_outputoverflow to control input flows.
->output_bufsize($output_bufsize)
Get/set the size of the output buffer.
->autoread($autoread)
Get/set automatic reading if data when data can be read. Without autoread turned on, the input buffer ins't filled and none of the read methods will work. The point of this is for working with non-data filehandles. This is an experts-only method that kinda defeats the purpose of this module. This would be necessary using recv() to get data.
->drain()
Used to start looking for write-ready events on the underlying filehandle. In normal operation this is handled automatically. Deprecated: use writeevents(1) instead.
->reentrant($reentrant)
Get/set reentrant callbacks. By default, IO::Event avoids making reentrant callbacks. This is good because your code is less likely to break. This is bad because you won't learn about things right away. For example, you will not learn the the output buffer is overflowing during print(). You'll have to wait for the output buffer to begin draining to find out. This could be a problem.
->close()
If there is output buffered, close will be delayed until the output buffer drains.
->forceclose
Close close immediately, even if there is output buffered.
->ie_desc([new description])
Returns (and sets) the text description of the filehandle. For debugging.

The following timer construction arguments are supported by IO::Event's emulated event loop and IO::Event's API on top of AnyEvent:

A callback to invoke when the timer goes off. The callback can either be a CODE reference or an array reference. If it's an array reference, the array should be a two element tuple: the first element is an object and the second object is a method to invoke on the object. The only argument to the method call a reference to the timer object: 

 my ($object, $method) = @{$timer->{cb}}
 $object->$method($timer)
A time at which to invoke the callback.
An interval, in seconds between repeat invocations of the callback.
The interval until the first invocation of the callback. After that, invoke every interval.

The following methods (from Event) are supported on timer objects: start(), again(), now(), stop(), cancel(), is_cancelled(), is_running(), is_suspended(), pending.

The following idle construction arguments are supported by IO::Event's emulated event loop and IO::Event's API on top of AnyEvent:

A callback to invoke when the event loop is idle. The callback can either be a CODE reference or an array reference. If it's an array reference, the array should be a two element tuple: the first element is an object and the second object is a method to invoke on the object. 

 my ($object, $method) = @{$timer->{cb}}
 $object->$method();
The minimum time between invocations of the callback.
The maximum time between invocations of the callback.

The following methods (from Event) are supported on idle objects: start(), again(), now(), stop(), cancel(), is_cancelled(), is_running(), is_suspended(), pending.

Any method invocations that fail because the method isn't defined in IO::Event will by tried twice more: once using trying for a method on the inner (hidden) filehandle and once more trying for a method on the Event object that's used to create the select loop for this module.

This dispatch is now deprecated with the choice of event handlers.

        # This is a tcp line echo server
        my $listener = IO::Event::Socket::INET->new(
                Listen => 10,
                Proto => 'tcp',
                LocalPort => 2821,
        );
        Event::loop();
        sub ie_connection
        {
                my ($pkg, $lstnr) = @_;
                my $client = $lstnr->accept();
                printf "accepted connection from %s:%s\n",
                        $client->peerhost, $client->peerport;
        }
        sub ie_input
        {
                my ($pkg, $client, $ibufref) = @_;
                print $client <$client>;
        }

sysread() is incompatible with eof() because eof() uses getc(). Most of the time this isn't a problem. In other words, some of the time this is a problem: lines go missing.

For this reason, IO::Event never uses sysread(). In fact, if you ask it to do a sysread() it does a read() for you instead.

On the other hand, at the current time no problems with syswrite have come to light and IO::Event uses syswrite and never any other form of write/print etc.

IO::Event keeps copies of all of its registered filehandles. If you want to close a filehandle, you'll need to actually call close on it.

The filehandle object itself is a funny kind of hash reference. If you want to use it to store your own data, you can. Please don't use hash keys that begin "ie_" or "io_" as those are the prefixes used by "IO::Event" and "IO::Socket".

The syntax is kinda funny:

        ${*$filehandle}{'your_hash_key'}

For a different API on top of IO::Event, see IO::Event::Callback. It uses IO::Event but provides a simpler and perhaps easier-to-use API.

The following perl modules do something that is kinda similar to what is being done here:

AnyEvent::Handle, AnyEvent::AIO, IO::AIO, IO::Multiplex, IO::NonBlocking, IO::Select Event, POE, POE::Component::Server::TCP, Net::Socket::NonBlock, Net::Server::Multiplex, NetServer::Generic

The API borrows most heavily from IO::Multiplex. IO::Event uses Event.pm and thus can be used in programs that are already using Event or POE.

Since the original writing of IO::Event, AnyEvent has been released and now AnyEvent::AIO and <AnyEvent:Handle> should be considered the only good alternatives to IO::Event.

For an example program using IO::Event, see IO::Event::rinetd which used to be included in this package.

The test suite only covers 40% of the code. The module is used by its author and seems solid.

Copyright (C) 2002-2009 David Muir Sharnoff <muir@idiom.org>. Copyright (C) 2011-2013 Google, Inc. This module may be used/copied/etc on the same terms as Perl itself.

This module is packaged for Fedora by Emmanuel Seyman <emmanuel@seyman.fr>

2022-06-14 perl v5.34.0