[jboss-jira] [JBoss JIRA] Commented: (JGRP-518) RpcDispatcher: filter for accepting incoming responses

[Bela Ban (JIRA)]

    [ http://jira.jboss.com/jira/browse/JGRP-518?page=comments#action_12370241 ] 
            
Bela Ban commented on JGRP-518:
-------------------------------

#1 What do you want to do if none of the responses are acceptable ? Timeout ?
#2 How should 'discarded' (not accepted) responses look like in the RspList ? As not-received ?

I would probably have to create a new mode GET_WITH_FILTER, which requires a valid filter. Hmm, I could also *not* do this and leave it up to the user to make sure that the filter always returns: for example, if you have mode GET_ALL, and discard only 1 valid response, and don't have a timeot, you'd block forever.

Idea: if I marked every response I received which PASSED the filter as RECEIVED and every response which FAILED the filter as RECEIVED_NOT_ACCEPTED, then we'd know exactly which responses passed and which ones failed.

Hmm, not good either: GET_FIRST would return as soon as 1 passed or failed response is received; it it is failed then we'd return with a response which didn't pass the filter.

Okay, so the simple solution is then to just drop all responses which don't pass the filter, and it is the programmer's responsibility to make sure the call doesn't hang forever ! Example:

- We expect responses from A,B,C
- Mode is GET_ALL and timeout is 0 (wait forever)
- Get get a response from A, discard it
- Get responses from B and C
==> We hang forever


> RpcDispatcher: filter for accepting incoming responses
> ------------------------------------------------------
>
>                 Key: JGRP-518
>                 URL: http://jira.jboss.com/jira/browse/JGRP-518
>             Project: JGroups
>          Issue Type: Feature Request
>            Reporter: Manik Surtani
>         Assigned To: Bela Ban
>             Fix For: 2.6
>
>
> [Manik's email]
> Are there any plans to implement a way to register a filter when using the RpcDispatcher when waiting for results?
> Current options (GroupRequest.GET_ALL, GET_NONE, GET_MOST, GET_FIRST, etc) is insufficient where you want the call to block until the first *acceptable* response is received.
> Basically, if I expect responses from everyone in the cluster but want to wait for the first acceptable response, I have no choice but to do a GET_ALL and then parse all the responses for the first acceptable one.  Now the definition of an acceptable response is application-specific, and so perhaps a mechanism to register a filter would be useful.  Perhaps something like:
>     RpcDispatcher.callRemoteMethods(Vector dests, MethodCall call, int mode, long timeout, boolean use_anycasting, ResponseFilter responseFilter)
>     public interface ResponseFilter
>     {
>         boolean isAcceptable(Object response);
>     }
> If a filter is provided, only responses that pass the isAcceptable() test is added to the response list.  Then GroupRequest.GET_FIRST could be used and we could have a very efficient mechanism of not having to wait for all responses. 

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