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NAME
POE::Component::PubSub - A generic publish/subscribe POE::Component that
enables POE::Sessions to publish events to which other POE::Sessions may
subscribe.
VERSION
Version 0.04
SYNOPSIS
# Instantiate the publish/subscriber with the alias "pub"
POE::Component::PubSub->new('pub');
# Publish an event called "FOO". +PUBLISH_OUTPUT is actually optional.
$_[KERNEL]->post('pub', 'publish', 'FOO', +PUBLISH_OUTPUT);
# Elsewhere, subscribe to that event, giving it an event to call # when
the published event is fired. $_[KERNEL]->post('pub', 'subscribe',
'FOO', 'FireThisEvent');
# Fire off the published event $_[KERNEL]->post('pub', 'FOO');
# Publish an 'input' event $_[KERNEL]->post('pub', 'publish', 'BAR',
+PUBLISH_INPUT, 'MyInputEvent');
# Tear down the whole thing $_[KERNEL]->post('pub', 'destroy');
EVENTS
All public events do some sanity checking to make sure of a couple of
things before allowing the events such as checking to make sure the
posting session actually owns the event it is publishing, or that the
event passed as the return event during subscription is owned by the
sender. When one of those cases comes up, an error is carp'd, and the
event returns without stopping execution.
'publish'
This is the event to use to publish events. It accepts one argument,
the event to publish. The published event may not already be
previously published. The event may be completely arbitrary and does
not require the publisher to implement that event. Think of it as a
name for a mailing list.
You can also publish an 'input' or inverse event. This allows for
arbitrary sessions to post to your event. In this case, you must
supply the optional published event type and the event to be called
when the published event fires.
There are two types: PUBLISH_INPUT and PUBLISH_OUTPUT. PUBLISH_OUPUT
is implied when no argument is supplied.
'subscribe'
This is the event to use when subscribing to published events. It
accepts two arguments: 1) the published event, and 2) the event name
of the subscriber to be called when the published event is fired.
The event doesn't need to be published prior to subscription to
resolve chicken and egg problems in an async environment. But, the
sender must own and implement the return event.
'rescind'
Use this event to stop publication of an event. It accepts one
argument, the published event. The event must be published, and
published by the sender of the rescind event. If the published event
has any subscribers, a warning will be carp'd but execution will
continue.
'cancel'
Cancel subscriptions to events with this event. It accepts one
argment, the published event. The event must be published and the
sender must be subscribed to the event.
'_default'
After an event is published, the publisher may arbitrarily fire that
event to this component and the subscribers will be notified by
calling their respective return events with whatever arguments are
passed by the publisher. The event must be published, owned by the
publisher, and have subscribers for the event to be propagated. If
any of the subscribers no longer has a valid return event their
subscriptions will be cancelled and a warning will be carp'd.
'listing'
To receive an array reference containing tuples of the event name,
and the type of the events that are currently published within the
component, call this event. It accepts one argument, the return
event to fire with the listing. The sender must own the return
event.
'destroy'
This event will simply destroy any of its current state and remove
any and all aliases this session may have picked up. This should
free up the session for garbage collection.
CLASS METHODS
POE::Component::PubSub->new($alias)
This is the constructor for the publish subscribe component. It
instantiates it's own session using the provided $alias argument to
set its kernel alias. If no alias is provided, the default alias is
'PUBLISH_SUBSCRIBE'.
DEBUGGING
$POE::Component::PubSub::TRACE_AND_DEBUG
To enable debugging within the component at the POE::Session level
and also with various warnings, set this variable to logical true
BEFORE calling new().
NOTES
Right now this component is extremely simple, but thorough when it comes
to checking the various requirements for publishing and subscribing.
Currently, there is no mechanism to place meta-subscriptions to the
events of the component itself. This feature is planned for the next
release.
Also, to do some of the checking on whether subscribers own the return
events, some ideas were lifted from POE::API::Peek, and like that
module, if there are changes to the POE core, they may break this
module.
AUTHOR
Nicholas R. Perez, "<nperez at cpan.org>"
BUGS
Please report any bugs or feature requests to "bug-poe-component-pubsub
at rt.cpan.org", or through the web interface at
<http://rt.cpan.org/NoAuth/ReportBug.html?Queue=POE-Component-PubSub>. I
will be notified, and then you'll automatically be notified of progress
on your bug as I make changes.
SUPPORT
You can find documentation for this module with the perldoc command.
perldoc POE::Component::PubSub
You can also look for information at:
* AnnoCPAN: Annotated CPAN documentation
<http://annocpan.org/dist/POE-Component-PubSub>
* CPAN Ratings
<http://cpanratings.perl.org/d/POE-Component-PubSub>
* RT: CPAN's request tracker
<http://rt.cpan.org/NoAuth/Bugs.html?Dist=POE-Component-PubSub>
* Search CPAN
<http://search.cpan.org/dist/POE-Component-PubSub>
COPYRIGHT & LICENSE
Copyright 2008-2009 Nicholas R. Perez, all rights reserved.
This program is released under the following license: gpl
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