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https://issues.apache.org/jira/browse/ZOOKEEPER-890?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12919094#action_12919094
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Austin Shoemaker commented on ZOOKEEPER-890:
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That sounds like a good design. Perhaps it could be clarified in the
documentation?
http://hadoop.apache.org/zookeeper/docs/r3.3.1/zookeeperProgrammers.html#ch_zkWatches
If this is correct behavior then the Python client needs to be fixed to not
delete the watcher on session events. Will file a separate bug on that.
> C client invokes watcher callbacks multiple times
> -------------------------------------------------
>
> Key: ZOOKEEPER-890
> URL: https://issues.apache.org/jira/browse/ZOOKEEPER-890
> Project: Zookeeper
> Issue Type: Bug
> Components: c client
> Affects Versions: 3.3.1
> Environment: Mac OS X 10.6.5
> Reporter: Austin Shoemaker
> Priority: Critical
> Attachments: watcher_twice.c, ZOOKEEPER-890.patch
>
>
> Code using the C client assumes that watcher callbacks are called exactly
> once. If the watcher is called more than once, the process will likely
> overwrite freed memory and/or crash.
> collect_session_watchers (zk_hashtable.c) gathers watchers from
> active_node_watchers, active_exist_watchers, and active_child_watchers
> without removing them. This results in watchers being invoked more than once.
> Test code is attached that reproduces the bug, along with a proposed patch.
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