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From "Martin Traverso (JIRA)" <j...@apache.org>
Subject [jira] Commented: (ZOOKEEPER-666) Unsafe publication in client API
Date Thu, 11 Feb 2010 07:17:28 GMT

    [ https://issues.apache.org/jira/browse/ZOOKEEPER-666?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12832405#action_12832405
] 

Martin Traverso commented on ZOOKEEPER-666:
-------------------------------------------

Indeed, breaking backward-compatibility would be a big issue.

One drawback I see with 2b is that the API would seem to allow calling those methods after
connect() has been called. What would the semantics be in that scenario?

How about a builder-based approach instead? E.g,

{noformat}
ZooKeeper client = ZooKeeper.builder()
                            .timeout(...)
                            .watcher(...)
                            .connect(connectString);
{noformat}

This would make it possible to add future parameters without breaking the public API, while
preserving immutability semantics for initialization parameters.

> Unsafe publication in client API
> --------------------------------
>
>                 Key: ZOOKEEPER-666
>                 URL: https://issues.apache.org/jira/browse/ZOOKEEPER-666
>             Project: Zookeeper
>          Issue Type: Bug
>          Components: java client
>    Affects Versions: 3.2.2
>            Reporter: Martin Traverso
>             Fix For: 3.3.0
>
>
> The following code may result in a data race due to unsafe publication of a reference
to "this". The call to cnxn.start() spawns threads that have access to the partially-constructed
reference to the ZooKeeper object. 
> See http://www.ibm.com/developerworks/java/library/j-jtp0618.html for some background
info.
> {noformat}
> public ZooKeeper(String connectString, int sessionTimeout, Watcher watcher)
>     throws IOException
> {
>         .....
>         cnxn = new ClientCnxn(connectString, sessionTimeout, this, watchManager);
>         cnxn.start();
> }
> {noformat}
> The obvious fix is to move the call to cnxn.start() into a separate start() method.

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