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Zili Chen updated CURATOR-504: ------------------------------ Fix Version/s: 5.4.0 (was: 5.5.0) > Race conditions in LeaderLatch after reconnecting to ensemble > ------------------------------------------------------------- > > Key: CURATOR-504 > URL: https://issues.apache.org/jira/browse/CURATOR-504 > Project: Apache Curator > Issue Type: Bug > Affects Versions: 4.1.0 > Reporter: Yuri Tceretian > Assignee: Zili Chen > Priority: Minor > Fix For: 5.4.0 > > Attachments: 51868597-65791000-231c-11e9-9bfa-1def62bc3ea1.png, > Screen Shot 2019-01-31 at 10.26.59 PM.png, > XP91JuD048Nl_8h9NZpH01QZJMfCLewjfd2eQNfOsR6GuApPNV.png > > > 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. > Below is an approximate diagram of what happens: > !51868597-65791000-231c-11e9-9bfa-1def62bc3ea1.png|width=1261,height=150! -- This message was sent by Atlassian Jira (v8.20.10#820010)