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Special Forums News, Links, Events and Announcements Complex Event Processing RSS News DEBS08(4) - Event-based Middleware Post 302212413 by Linux Bot on Monday 7th of July 2008 01:00:03 PM
Old 07-07-2008
DEBS08(4) - Event-based Middleware

vincent
Mon, 07 Jul 2008 12:26:30 +0000
Continuing on with the Distributed Event Based Systems conference, its quite surprising that the presentations on event transmission (aka intelligent middleware, content-based pub-sub, clustering pub-sub nodes for performance, secure pub-sub etc etc) and of event processing (CEP, ESP, Bayes/rules/uncertainty/queries etc etc) are not in different “streams”, given they have different audiences. From a CEP perspective, middleware is certainly necessary (and for TIBCO, er, pretty relevant), but our interest is more on what to do with events, not worry about how they arrive.
Having said that, there is clearly a connection between “intelligent / optimal distribution of events” and “distributed (complex) event processing”. And “dynamic routing” implies “intelligent nodes” that are, in effect, limited event processing agents. So the concepts are connected, although the R&D goals may, today, differ (e.g. middleware: routing resilience, performance and scaleability; CEP: event processing scaleability, performance and resilience…).
A few observations were:
  • In a presentation on gaming events, the definition of Event included an “obsolete” attribute, used to indicate an event whose existance is made “irrelevant” by some subsequent event(s). I’m not sure this is a generic attribute of all events, though - the event still happened, and could be correlated (for example to identify the speed at which such events become obscolete). So this is probably useful in some contexts, and not others.
  • An event metamodel was presented by the University of Waterloo in Canada, which was much more comprehensive (/complex) that the definition we use in TIBCO BusinessEvents (for Event Processing). But their goal, to make “event” a first class entity, is shared by the OMG EMP team, with whom the Waterloo group should probably be collaborating.
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EVENT(3)								 1								  EVENT(3)

The Event class

INTRODUCTION
Event class represents and event firing on a file descriptor being ready to read from or write to; a file descriptor becoming ready to read from or write to(edge-triggered I/O only); a timeout expiring; a signal occuring; a user-triggered event. Every event is associated with EventBase . However, event will never fire until it is added (via Event::add ). An added event remains in pending state until the registered event occurs, thus turning it to active state. To handle events user may register a callback which is called when event becomes active. If event is configured persistent , it remains pending. If it is not persistent, it stops being pending when it's callback runs. Event::del method deletes event, thus making it non-pending. By means of Event::add method it could be added again. CLASS SYNOPSIS
Event final Event Constants o const integer$Event::ET32 o const integer$Event::PERSIST16 o const integer$Event::READ2 o const integer$Event::WRITE4 o const integer$Event::SIGNAL8 o const integer$Event::TIMEOUT1 Properties o publicreadonly bool$pending Methods o public bool Event::add ([double $timeout]) o public bool Event::addSignal ([double $timeout]) o public bool Event::addTimer ([double $timeout]) o public Event::__construct (EventBase $base, mixed $fd, int $what, callable $cb, [mixed $arg = NULL]) o public bool Event::del (void ) o public bool Event::delSignal (void ) o public bool Event::delTimer (void ) o public void Event::free (void ) o publicstatic array Event::getSupportedMethods (void ) o public bool Event::pending (int $flags) o public bool Event::set (EventBase $base, mixed $fd, [int $what], [callable $cb], [mixed $arg]) o public bool Event::setPriority (int $priority) o public bool Event::setTimer (EventBase $base, callable $cb, [mixed $arg]) o publicstatic Event Event::signal (EventBase $base, int $signum, callable $cb, [mixed $arg]) o publicstatic Event Event::timer (EventBase $base, callable $cb, [mixed $arg]) PROPERTIES
o $pending - Whether event is pending. See About event persistence . PREDEFINED CONSTANTS
o Event::ET - Indicates that the event should be edge-triggered, if the underlying event base backend supports edge-triggered events. This affects the semantics of Event::READ and Event::WRITE . o Event::PERSIST - Indicates that the event is persistent. See About event persistence . o Event::READ - This flag indicates an event that becomes active when the provided file descriptor(usually a stream resource, or socket) is ready for reading. o Event::WRITE - This flag indicates an event that becomes active when the provided file descriptor(usually a stream resource, or socket) is ready for reading. o Event::SIGNAL - Used to implement signal detection. See "Constructing signal events" below. o Event::TIMEOUT - This flag indicates an event that becomes active after a timeout elapses. The Event::TIMEOUT flag is ignored when constructing an event: one can either set a timeout when event is added , or not. It is set in the $what argument to the callback function when a timeout has occurred. PHP Documentation Group EVENT(3)
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