dafu created HELIX-124:
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Summary: race condition in ZkHelixManager.handleNewSession()
Key: HELIX-124
URL: https://issues.apache.org/jira/browse/HELIX-124
Project: Apache Helix
Issue Type: Bug
Reporter: dafu
ZkHelixManager.handleNewSession() is an async callback. There is a race
condition when we have multiple consecutive session expiries. for example:
1) sessionExpiry_0 happens, and newSessionId is sessionId_1
2) sessionExpiry_1 happens, and newSessionId is sessionId_2
3) handleNewSession caused by sessionExpiry_0 is invoked
4) handleNewSession caused by sessionExpiry_1 is invoked
Since 3) and 4) both happen after 2), we will get zk handleNewSession callback
twice with the same session id (sessionId_2)
This is problematic:
if the manager is a PARTICIPANT, the second handleNewSession() will fail to
create live-instance and reset all listeners. then we come to the situation
where live-instance exists but no listener is registered for the PARTICIPANT
if the manager is a CONTROLLER, we add listeners twice
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