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Manual Reference Pages  -  POE::COMPONENT::PUBSUB (3)

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POE::Component::PubSub - A generic publish/subscribe POE::Component that enables POE::Sessions to publish events to which other POE::Sessions may subscribe.



Version 0.04


# 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’);


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.


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’.


$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().


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.


Nicholas R. Perez, <nperez at>


Please report any bugs or feature requests to bug-poe-component-pubsub at, or through the web interface at <>. I will be notified, and then you’ll automatically be notified of progress on your bug as I make changes.


You can find documentation for this module with the perldoc command.

    perldoc POE::Component::PubSub

You can also look for information at:
o AnnoCPAN: Annotated CPAN documentation


o CPAN Ratings


o RT: CPAN’s request tracker


o Search CPAN



Copyright 2008-2009 Nicholas R. Perez, all rights reserved.

This program is released under the following license: gpl

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