[HELIX-124] race condition in ZkHelixManager.handleNewSession()

• Type: Sub-task
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 0.6.2-incubating
• Sprint: Sprint #4 10/2 - 10/16
• Assignee: Zhen Zhang
• Reporter: Zhen Zhang
• Created: 06/Jun/13 18:06
• Updated: 12/Nov/13 23:37
• Resolved: 06/Aug/13 21:11

Description

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