[ZOOKEEPER-911] move operations from methods to individual classes

• Type: New Feature
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Component/s: java client
• Assignee: Thomas Koch
• Reporter: Thomas Koch
• Created: 21/Oct/10 15:02
• Updated: 03/Feb/22 08:50

Description

Copied from my email to the ZK dev list from 2010/05/26:

For my current code I'm using zkclient[1] and have also looked at cages[2] for
some ZK usage examples. I observed, that there's a common pattern to wrap ZK
operations in callables and feed them to a "retryUntilConnected" executor.

Now my idea is, that ZK should already come with operations in classes, e.g.:

o.a.z.operation.Create extends Operation implements callable{

private path, data[], acl, createMode

public Create( .. all kind of ctors .. )

public call()

{ .. move code from Zookeeper.create() here }

}

Similiar classes should be provided for getChildren, delete, exists, getData,
getACL, setACL and setData.

One could then feed such operations to an ZkExecutor, which has the necessary
knowledge about the ZkConnection and can execute a command either
synchronously or asynchronously.

One could also wrap operations in an ExceptionCatcher to ignore certain
Exceptions or in a RetryPolicy.

This is only an idea so far, but I wanted to share my thoughts before starting
to try it out. (BTW: You can meet me at BerlinBuzzwords.de)

[1] http://github.com/sgroschupf/zkclient
[2] http://code.google.com/p/cages/

And a reply from Patrick Hunt at my mail:

Hi Thomas, you might take a look at this JIRA
https://issues.apache.org/jira/browse/ZOOKEEPER-679

there's definitely been interest in this area, however there are some
real challenges as well. Most users do end up wrapping the basic api
with some code, esp the "retry" metaphor is a common case, so I think it
would be valuable. At the same time getting the semantics right is hard
(and covering all the corner cases). Perhaps you could sync up with
Aaron/Chris, I'd personally like to see this go into contrib, but I
understand the extra burden the patch process presents – it may make
more sense to rapidly iterate on something like github and then move to
contrib once you have something less frequently changing, where the
patch issue would be less of a problem (see 679, there's discussion on
this there). Regardless which way you take it we'd be happy to work with
you.

Issue Links

• depends upon: ZOOKEEPER-837 cyclic dependency ClientCnxn, ZooKeeper
• is related to: ZOOKEEPER-965 Need a multi-update command to allow multiple znodes to be updated safely