[HDFS-4029] GenerationStamp should use an AtomicLong

• Type: Sub-task
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 2.0.0-alpha
• Fix Version/s: 2.0.3-alpha
• Component/s: namenode
• Hadoop Flags: Reviewed
• Assignee: Eli Collins
• Reporter: Eli Collins
• Created: 10/Oct/12 22:52
• Updated: 15/Feb/13 13:12
• Resolved: 17/Oct/12 05:00

Description

GenerationStamp#genstamp is a volatile long. Incrementing volatiles is not thread safe, which is currently not an issue because the only increment is done in nextStamp which is synchronized (theoretically setStamp could race with nextStamp though that wouldn't happen given the current code). It would be cleaner to use an AtomicLong so that genstamp itself is atomic and we don't have to synchronize the various accesses to it.