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https://issues.apache.org/jira/browse/CURATOR-644?focusedWorklogId=804387&page=com.atlassian.jira.plugin.system.issuetabpanels:worklog-tabpanel#worklog-804387
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ASF GitHub Bot logged work on CURATOR-644:
------------------------------------------
Author: ASF GitHub Bot
Created on: 29/Aug/22 13:52
Start Date: 29/Aug/22 13:52
Worklog Time Spent: 10m
Work Description: XComp commented on PR #430:
URL: https://github.com/apache/curator/pull/430#issuecomment-1230339944
> they're logically resolved simultaneously. That is, if you resolve
CURATOR-644, you resolve CURATOR-645 - they're the same sort.
>
> In another word, you can check out the diff and tell me how to split it up
into two PRs.
I was thinking about it once more. CURATOR-645 could be covered separately
in my opinion. CURATOR-645 was identified in FLINK-27078 where we run almost no
logic before revoking the leadership by calling `LeaderLatch#close`. That
caused the current leader's `LeaderLatch` instance to trigger its child node
deletion while other `LeaderLatch` instances were right within setting up the
watcher for its child node's predecessor.
Hence, I see CURATOR-645 being not that tightly related with the reconnect
issue covered in CURATOR-644. CURATOR-645 just needs to be resolved before
CURATOR-644 can be resolved.
Anyway, the changes are not that big in the end that we couldn't resolve
both in the same PR. ¯\_(ツ)_/¯
Issue Time Tracking
-------------------
Worklog Id: (was: 804387)
Time Spent: 1h 40m (was: 1.5h)
> CLONE - Race conditions in LeaderLatch after reconnecting to ensemble
> ---------------------------------------------------------------------
>
> Key: CURATOR-644
> URL: https://issues.apache.org/jira/browse/CURATOR-644
> Project: Apache Curator
> Issue Type: Bug
> Affects Versions: 4.2.0
> Reporter: Ken Huang
> Assignee: Jordan Zimmerman
> Priority: Minor
> Time Spent: 1h 40m
> Remaining Estimate: 0h
>
> Clone from CURATOR-504.
> We use LeaderLatch in a lot of places in our system and when ZooKeeper
> ensemble is unstable and clients are reconnecting to logs are full of
> messages like the following:
> {{{}[2017-08-31
> 19:18:34,562][ERROR][org.apache.curator.framework.recipes.leader.LeaderLatch]
> Can't find our node. Resetting. Index: -1 {{}}}}
> According to the
> [implementation|https://github.com/apache/curator/blob/4251fe328908e5fca37af034fabc190aa452c73f/curator-recipes/src/main/java/org/apache/curator/framework/recipes/leader/LeaderLatch.java#L529-L536],
> this can happen in two cases:
> * When internal state `ourPath` is null
> * When the list of latches does not have the expected one.
> I believe we hit the first condition because of races that occur after client
> reconnects to ZooKeeper.
> * Client reconnects to ZooKeeper and LeaderLatch gets the event and calls
> reset method which set the internal state (`ourPath`) to null, removes old
> latch and creates a new one. This happens in thread
> "Curator-ConnectionStateManager-0".
> * Almost simultaneously, LeaderLatch gets another even NodeDeleted
> ([here|https://github.com/apache/curator/blob/4251fe328908e5fca37af034fabc190aa452c73f/curator-recipes/src/main/java/org/apache/curator/framework/recipes/leader/LeaderLatch.java#L543-L554])
> and tries to re-read the list of latches and check leadership. This happens
> in the thread "main-EventThread".
> Therefore, sometimes there is a situation when method `checkLeadership` is
> called when `ourPath` is null.
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