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From "dafu (JIRA)" <j...@apache.org>
Subject [jira] [Created] (HELIX-124) race condition in ZkHelixManager.handleNewSession()
Date Thu, 06 Jun 2013 18:07:20 GMT
dafu created HELIX-124:
--------------------------

             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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