On 16 Oct 2006, at 15:37, Jean-Marc Orliaguet wrote:
Florent Guillaume wrote:
On 16 Oct 2006, at 14:15, Florent Guillaume wrote:
The whiteboard pattern for events and dependencies is defined here:
http://www.osgi.org/documents/osgi_technology/whiteboard.pdf
Apparently the traditional Java pattern for synchronous event
subscription (used for extension) is of having each subscriber
for a given kind of event register with the event source -- the
event source maintains a list of people interested in it. This
pattern doesn't scale well, as the paper above explains, and has
many disadvantages (debugging, event observing, additionnal
classes needed, vector allocation, etc).
The Zope event model of having a registry between the event
source and the event listener is much better, and that's roughly
what OSGi calls the "whiteboard" pattern. In the Zope case the
registry is the adapter registry, in OSGi the bundle registry is
used.
I mean, the service registry, of course.
Some people much prefer the whiteboard pattern over Eclipse
extension point:
http://www.mail-archive.com/[email protected]/msg00091.html
My question is: how does this compare to what we use in
NXRuntime? What's our pattern?
Florent
I think that's more or less what I have in:
http://svn.nuxeo.org/trac/nuxeo/browser/NXThemes/NXThemesCore/trunk/
src/org/nuxeo/theme/events
EventManager.java is the event registry, event types are stored in
a central type registry.
all event listeners (handlers) have an event type, and the event
type is used as a key to look up events by type.
event sources call a Manager.notify(context) by passing an event
context (with the event source and the event target), and the event
manager finds listeners and call handle(context) on them
but that's more or less the way it was implemented in CPS3 already,
with a central registry?
What the paper advocates is to reuse the OSGi registry itself as the
central registry for this kind of thing.
It's able to do matching on arbitrary properties to find the service/
component to use.
It's very possible you won't like it because it reminds you too much
of the central Zope 3 adapter registry :) But I'm sure this has
advantages.
Florent
--
Florent Guillaume, Nuxeo (Paris, France) Director of R&D
+33 1 40 33 71 59 http://nuxeo.com [EMAIL PROTECTED]
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