On 10/26/12 7:13 PM, Scott Ferguson wrote:
> http://java.net/jira/browse/WEBSOCKET_SPEC-21
> http://java.net/jira/browse/WEBSOCKET_SPEC-37
>
> This is an important issue.
>
> In particular, the @WebSocketMessage methods really want to operate on
> beans that are scoped to the connection/session (using the standard
> @PostConstruct, @PreDestroy for lifecycle.) They're basically
> MessageHandlers, not endpoints, and should have the same lifecycle as
> MessageHandlers.
>
> The @WebSocketOpen could be scoped to the application (as current,
> i.e. as Endpoint), but it might be cleaner to change it as well to be
> called on a new instance for each request (as if MessageHandler), to
> avoid recreating the old home/instance EJB model. Either way would be
> logical, but having a single lifecycle in the spec would be simpler to
> define/explain.
>
> So I'd suggest the cleanest change would be to instantiate a new
> instance for each connection/session.
I think I agree with you Scott.
The programmatic model in EDR is such that there is one instance of an
Endpoint per URL-path, and developers have the option of either creating
new MessageHandler instances per session, or of using the same instance
for all sessions. What we wrote about threading says their lifecycle
(onOpen, onClose, onError) methods may be called concurrently, but for
each session, the onMessage methods will be called sequentially.
So its a sort of hybrid, with a single threaded model for the
MessageHandlers and a multi-threaded (servlet-like) model for the
Endpoint instances (see section 7.1). I remember this arose back in the
summer from a discussion we had on threading.
The annotation model is servlet-like, multiple threads can be in any of
the annotated methods.
After presenting this to the EE leads, there was a lot of feedback to
make the model simpler for developers: a new instance of Endpoint per
session/connection. i.e. the default mode for Endpoint is CDI request
scoped in the EE setting. Then all of onOpen, onClose, onError AND
onMessage are all callbacks in the context of one session/connection,
and called with only one thread at a time.
Annotated POJOs would then assume the same cardinality: a new POJO
instance per connection (per VM). Any of the websocket annotated methods
called by one thread at a time.
How do the others feel about defining things this way ?
Thanks,
- Danny
>
> (Also, I assume each onMessage is in a new CDI RequestScope (?))
>
> (Also, the 7.3.2 CDI injection into MessageHandlers doesn't make sense
> to me. In the current API, the developer instantiates the handler and
> therefore it would be weird for CDI to inject anything.)
>
> -- Scott
>
--
<http://www.oracle.com> *Danny Coward *
Java EE
Oracle Corporation