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From "Patrick Hunt (JIRA)" <j...@apache.org>
Subject [jira] Commented: (ZOOKEEPER-666) Unsafe publication in client API
Date Thu, 11 Feb 2010 06:16:27 GMT

    [ https://issues.apache.org/jira/browse/ZOOKEEPER-666?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12832392#action_12832392
] 

Patrick Hunt commented on ZOOKEEPER-666:
----------------------------------------

Yes, the subclassing issue in particular is nasty. We've fixed a number of these in the server
implementation already (not all iirc). In this case I'm not sure if we can do it in 3.3.0
though. It's too 
near term and the solution for this is going to be disruptive - the main public client interface
needs
to be changed.

I suspect that we should 

1) deprecate the existing constructors
2a) either add a new empty constructor and a "connect(connect, watcher,timeout)
or 
2b) add a new empty constructor, methods; setconnect/setwatcher(have alredy)/settimeout, and
a connect() string
(or perhaps connect(connectstring), etc...) One nice thing about this rather than 2a is that
we can add new
parameters in future w/o changing/overloading the connect(param1,param2,param3,...) method

existing users can migrate as they like (old methods deprecated)


> 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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