[jboss-as7-dev] Add Notification support to the domain management API

[Jeff Mesnil]

Le 6 mars 2013 à 08:53, Heiko Braun <hbraun at redhat.com> a écrit :

> 
> I have some questions regarding your example, where you describe that a notification is emitted (n1) when an attribute value changed and a client (curl) executes two subsequent POST requests (p1, p2) to fetch notifications. 
> 
> I am wondering what the semantics are for processing/delivering notifications. What can clients expect?
> 
> - Stream of notifications: Clients get to see what exists at a given point in time. There is the possibility to miss notifications.
> 
> - Durable subscriptions: Regardless of a clients availability and polling interval, it will always get all notifications since the last time it connected. It's not possible to miss notifications.
> 
> - Time windows: Notifications are kept for a certain amount of time, during that interval clients get the same snapshot, regardless how many times they poll? It's possible to miss notifications if the polling frequency is much bigger then the window size.

None of the above.

I describe it at the end of this section[1]  but it may not be not clear enough.

One each POST request, the client will receive the N most recent notifications that were emitted since its last POST request. Once the POST response is sent, the server will flush the notifications held for this client. He will not receive twice the same notification.
It is possible to miss notifications if the client does not poll often enough and there are more than N notifications emitted. This is a compromise to prevent exhausting server memory by having clients register a listener and never poll its notifications that'll fill up the memory.
Having a sensible value for N (e.g. 1024) should leave enough time for a client to poll regularly and not miss most notifications.

Does that answer your question?

jeff

[1] https://community.jboss.org/wiki/AddNotificationSupportToTheDomainManagementAPI#Notification_Handlers_Notifications_Resource

-- 
Jeff Mesnil
JBoss, a division of Red Hat
http://jmesnil.net/