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From "Appy (JIRA)" <j...@apache.org>
Subject [jira] [Comment Edited] (HBASE-18898) Provide way for the core flow to know whether CP implemented each of the hooks
Date Fri, 29 Sep 2017 01:47:00 GMT

    [ https://issues.apache.org/jira/browse/HBASE-18898?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16185234#comment-16185234
] 

Appy edited comment on HBASE-18898 at 9/29/17 1:46 AM:
-------------------------------------------------------

The only way i can think of to do this is:
Say we want to do this for MasterObserver
- In MasterCPHost constructor, do reflection over MasterObserver, get all its methods and
make a map.
- As CPs are loaded, check all the methods in its observer (if getMasterObserver() returns
one)
- If and only if
  ** The method signature matches one from MasterObserver
  ** The method is non-default
  Mark in that map that we have a CP needing that hook.
- In the wrappers we have in MasterCPHost for the hooks, (and this is the ugly part) do a
reflection to check if any CP is using that hook.



was (Author: appy):
The only way i can think of to do this is:
Say we want to do this for MasterObserver
- In MasterCPHost, do reflection over MasterObserver, get all its methods and make a map.
- As CPs are loaded, check all the methods in their observer
- If and only if
  ** The method signature matches one from MasterObserver
  ** The method is non-default
  Mark that we have a CP overriding that method
- In the hook wrappers we have in MasterCPHost, (and this is the ugly part) do a reflection
to check if any CP is using that hook.


> Provide way for the core flow to know whether CP implemented each of the hooks
> ------------------------------------------------------------------------------
>
>                 Key: HBASE-18898
>                 URL: https://issues.apache.org/jira/browse/HBASE-18898
>             Project: HBase
>          Issue Type: Improvement
>          Components: Coprocessors, Performance
>            Reporter: Anoop Sam John
>            Assignee: Anoop Sam John
>            Priority: Critical
>
> This came as a discussion topic at the tale of HBASE-17732
> Can we have a way in the code (before trying to call the hook) to know whether the user
has implemented one particular hook or not? eg: On write related hooks only prePut() might
be what the user CP implemented. All others are just dummy impl from the interface. Can we
have a way for the core code to know this and avoid the call to other dummy hooks fully? Some
times we do some processing for just calling CP hooks (Say we have to make a POJO out of PB
object for calling) and if the user CP not impl this hook, we can avoid this extra work fully.
The pain of this will be more when we have to later deprecate one hook and add new. So the
dummy impl in new hook has to call the old one and that might be doing some extra work normally.
> If the CP f/w itself is having a way to tell this, the core code can make use. What am
expecting is some thing like in PB way where we can call 
> CPObject.hasPreXXXX(), then CPObject. preXXXX ().. Should not like asking users to impl
this extra ugly thing. When the CP instance is loaded in the RS/HM, that object will be having
this info also. 



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