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Module Version: 0.12   Source   Latest Release: IOMux-1.00


IOMux - simplify use of file-event loops


 IOMux is extended by


  use IOMux;
  use IOMux::Socket::TCP;

  my $mux    = IOMux->new;
  my $server = IOMux::Socket::TCP->new(...);


IOMux is designed to take the effort out of managing multiple socket, file or pipe connections within one process. It is essentially a really fancy front end to various kinds of event mechanisms, like select and poll. In addition to maintaining the event loop, all input and output of the data stream gets buffered for you which tends to be quite difficult in event driven programs.

On many platforms, the capabilities of various event mechanisms do differ a lot. Be careful which mechanism you pick. Test it! Read the man-pages which contain information about limitations and please contribute information you discover.

See "DETAILS" far below for a long description about

. event managers select() and poll()
. managed file handles
. differences with IO::Multiplex and IO::Async, plus
. interesting implementation details.




There can only be one of these objects in your program. After instantiating this, you will add() file-handles and sockets. Finally, loop() is called to go into select-driven connection handling.

There are currently no OPTIONS, but they will probably arrive in the upcoming releases.


User interface


Add an HANDLER or BUNDLE to the multiplexer. Handlers extend IOMux::Handler. Bundles are related sets of handlers and extend IOMux::Bundle.


When this flag is set to true, the activities will end after having processed all currently flagged handles. All open handles when get closed cleanly.

The loop will also be terminated when all the handlers are removed (closed) That is a saver way to close the activities of your program where a call to endLoop() in many uses can be seen as tricky side-effect of a single handler.


Enter the main loop and start processing IO events. The loop will terminate when all handles are closed, serious errors emerge or endLoop() was called.

You may provide a HARTBEAT code reference, which will get called each time the internal select() has found a file handle with something to do or a timeout has expired. As arguments, it get the multiplexer object, the number of events and the time left to the next timeout. The validity of that third argument depends on the operating system and the actual muxer type.

example: loop

  exit 0;

example: loop with heartbeat

  sub hb($$)
  {   my ($mux, $count, $t) = @_;
$obj->open(MODE, PARAMS)

This open() provides a simplified interface to IOMux::Open, which on its turn is a simplification on using all kinds of handlers. See the manual of IOMux::Open for an extended description of the use.


  use IOMux::Open '-|';  # loads handler code
  sub print_line($$)
  {   my ($handler, $line) = @_;
      print "line = $line";

  # the short form
  my $who = $mux->open('-|', 'who');

  # equivalent to the longer
  my $who = IOMux::Open->new('-|', 'who');

  # or even longer
  use IOMux::Pipe::Read;
  my $who = IOMux::Pipe::Read->new(command => 'who');

For internal use

The following methods are provided, but end-users should avoid calling these methods directly: call them via the IOMux::Handler.


One of the connections wants to change its timeouts. A value of zero or undef means not active.

The correct OLDTIMEOUT must be provided to make it fast to detect whether this was the first timeout to expire. Checking the first timeout takes O(n) time, so we wish to avoid that.


  # set timeout
  $mux->changeTimeout($conn->fileno, undef, 10);

  # better this way

Change the select bit STATE for the FILENO. Change the READ, WRITE and/or EXCEPTion state.


  # clear read and except, keep write
  $mux->fdset($conn->fileno, 0, 1, 0, 1);

  # better this way:
  $conn->fdset(0, 1, 0, 1);
$obj->handler(FILENO, [HANDLER])

Returns (or sets) the handler which maintains FILENO.


  $mux->handler(1);   # probably STDOUT

Returns a list of all registered handlers (also the sockets).


  foreach my $conn ($mux->handlers) { ... }

Remove a connection from the multiplexer. Better to use the connection close method.



  # better this way:



Many components of IO-driven programming are quite platform dependent. Therefore, IOMux does not enforce the installation of these dependencies during installation. However, when you choose to use some of the components, you will discover you need to install additional modules. For instance, when you use IOMux::Poll you will need IO::Poll.

Many perl modules (like LWP) use autoloading to get additional code in when it gets used. This is a nice help for users who do not need to load those modules explicitly. It is also a speed-up for the boot-time of scripts. However, IOMux is usually run in a daemon (see examples/ directory) which should load all code before child processes are started. Besides, initialization time does not really matter for daemons.

Event managers

The following event managers are available on the moment:

Other possible mechanisms include epoll, ppoll, pselect, kqueue, and Glib, may get added later. Connections to other event frameworks as POE, IO::Async, and AnyEvent may get added as well.

File handles

The event managers looks to one or more file handles for changes: either the write buffer gets empty (the program may send more), requested data has arrived (ready to be read) or (unexpected) error text comes in.

The following handles are supported, although maybe not on your platform.



Difference to IO::Multiplex

The IOMux (Mux) implementation is much closer to IO::Multiplex (Plex) than you may expect. Similar enough to write a comparison.

Main differences:

. Event managers

In Plex, all is organized around a select loop. In Mux, you have a choice between various mechanisms of which some still need to be implemented.

. Callback objects

In Plex, the file-handle may have a callback object associated to it. If not, a default is used. In Mux, the callback has the focus, which has a file-handle associated to it. This use if the multiplexing select less visible this way, which should simplify implementations.

Mux does not support callbacks to name-spaces, because the object is used for per-handle administration. In Plex, that administration is located inside the multiplex object (and therefore difficult to extend with higher level applications)

. Callback routines

The Mux implementation defines the same mux_* methods as Plex, but has organized them. In Plex, the connection accepting mux_connection and the input callback mux_input are always available, even though the callback object will only support one of both (if your abstraction is correct). In Mux, there is a clear distinction between various kinds of handlers.

In Mux, you have a few more locations where you can hook the process, a few more callbacks.

. Pipes and files

Mux added support for file reading and writing, pipes and proxies.

. Timeouts

One should use timeouts on all handlers, because no connection can be trusted even files (which may come from stalled NFS partitions).

This module started as a rework of IO::Multiplex. It follows the same concept, but with major internal and visible improvements. Some core logic of this module has been derived from work by Bruce J Keeler and Rob Brown. Examples, tests and documentation are derived from their work as well.

IO::Async / Net::Async

Paul Evans has developed a large number of modules which is more feature complete than IOMux. It supports far more event loops, is better tested, and has many higher level applications ready to be used.

Certain applications will benefit from IOMux (especially my personal development projects), because it is based on the OODoc module for object oriented perl module documentation, and Log::Report for error handling and translations. Besides, the IO::Multiplex interface is much easier to use than the IO::Async concept.

On CPAN, you can find various alternatives for this module.


This module is part of IOMux distribution version 0.12, built on January 27, 2011. Website: All modules in this suite: "Any::Daemon", "IOMux", and "IOMux::HTTP".

Please post questions or ideas to


Copyrights 2011 by Mark Overmeer. For other contributors see ChangeLog.

This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself. See

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