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From "ASF GitHub Bot (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (ZOOKEEPER-2627) Remove ZRWSERVERFOUND from C client and replace handle_error with something more semantically explicit for r/w server reconnect.
Date Sat, 05 Nov 2016 21:05:58 GMT

    [ https://issues.apache.org/jira/browse/ZOOKEEPER-2627?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15640589#comment-15640589
] 

ASF GitHub Bot commented on ZOOKEEPER-2627:
-------------------------------------------

Github user rgs1 commented on a diff in the pull request:

    https://github.com/apache/zookeeper/pull/100#discussion_r86673245
  
    --- Diff: src/c/src/zookeeper.c ---
    @@ -2072,6 +2076,11 @@ static int ping_rw_server(zhandle_t* zh)
     
     out:
         close(sock);
    +    if (!rc) {
    +        addr_rw_server = 0;
    +    } else {
    +        addr_rw_server = &zh->addr_rw_server;
    +    }
    --- End diff --
    
    nit:
    
    ```
    addr_rw_server = rc ? &zh->addr_rw_server : 0;
    ```


> Remove ZRWSERVERFOUND from C client and replace handle_error with something more semantically
explicit for r/w server reconnect.
> --------------------------------------------------------------------------------------------------------------------------------
>
>                 Key: ZOOKEEPER-2627
>                 URL: https://issues.apache.org/jira/browse/ZOOKEEPER-2627
>             Project: ZooKeeper
>          Issue Type: Bug
>          Components: c client
>    Affects Versions: 3.5.2
>            Reporter: Michael Han
>            Assignee: Michael Han
>             Fix For: 3.5.3
>
>         Attachments: ZOOKEEPER-2627.patch
>
>
> While working on ZOOKEEPER-2014, I noticed a discrepancy between Java and C client regarding
the error codes definition. There is a {noformat}ZRWSERVERFOUND = -122{noformat} definition
in C client which is not present in Java client's KeeperException.Code definitions. 
> This discrepancy was introduced by ZOOKEEPER-827, where the C client logic was simulating
the Java client's logic when doing a read/write server search while client is in read only
mode. Once client finds a valid read/write server, client will try to disconnect and reconnect
with this read/write server, as we always prefer r/w server in ro mode. The way Java client
is doing this disconnect/reconnect process is by throwing a RWServerFoundException (instead
of a KeeperException) to set the client in disconnected state, then wait for client reconnect
with r/w server address set before throwing the exception. C client did similar but instead
of having an explicitly disconnect / clean up routine, the client was relying on handle_error
to do the job where ZRWSERVERFOUND was introduced.
> I propose we remove ZRWSERVERFOUND error code from C client and use an explicit routine
instead of handle_error when we do r/w server search in C client for two reasons:
> * ZRWSERVERFOUND is not something ZK client users would need to know. It's a pure implementation
detail that's used to alter the connection state of the client, and ZK client users have no
desire nor need to handle such errors, as R/W server scanning and connect is handled transparently
by ZK client library.
> * To maintain consistency between Java and C client regarding error codes definition.
Without removing this from C client, we would need to replace RWServerFoundException in Java
client with a new KeeperException, and again with the reason mentioned above, we don't need
a KeeperException for this because such implementation detail does not have to be exposed
to end users (unless, we provided alternative for users to opt-out automate R/W server switching
when in read only mode which we don't.).



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