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https://issues.apache.org/jira/browse/ZOOKEEPER-4625?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17732340#comment-17732340
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Kezhu Wang commented on ZOOKEEPER-4625:
---------------------------------------
Just for information, an [rust
client|https://github.com/kezhuw/zookeeper-client-rust] uses an [reference
counting
like|https://github.com/kezhuw/zookeeper-client-rust/blob/7466e867fb1b229d6b6ffb230e2e682c49ff494e/src/session/watch.rs#L368-L388]
solution to overcome this. It only issues {{removeWatches}} if there are no
more watchers with same watch mode on watching path(the code looks cumbersome
as it has to deal with ZOOKEEPER-4472).
> No reliable way to remove watcher without interfering others in same watch
> mode and on same path
> ------------------------------------------------------------------------------------------------
>
> Key: ZOOKEEPER-4625
> URL: https://issues.apache.org/jira/browse/ZOOKEEPER-4625
> Project: ZooKeeper
> Issue Type: Bug
> Components: java client
> Affects Versions: 3.8.0
> Reporter: Kezhu Wang
> Priority: Major
>
> It is possible that one node path could be watched more than once by
> different watchers in same watch mode and same ZooKeeper session.
> ZOOKEEPER-1910 reported this, but resorted to "checkWatches" to circumvent
> this. It leaks watches untouched in server side.
> I think it might be possible do some tracking works in client to support
> "removeWatches" without fearing client usages.
> Here are some links that lead to this issue:
> * ZOOKEEPER-1910: RemoveWatches wrongly removes the watcher if multiple
> watches exists on a path
> * CURATOR-654: DistributedBarrier watcher leak and its
> [pr|https://github.com/apache/curator/pull/435]
> * [Why removeWatches sends OpCode.checkWatches to the
> server?|https://lists.apache.org/thread/0kcnklcxs0s5656c1sbh3crgdodbb0qg]
> from mailing list.
> * [Drop for
> watcher|https://github.com/kezhuw/zookeeper-client-rust/issues/2] from an
> rust implementation.
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