[AMQ-3732] Different methods synchronizing on different mutexes when changing the same field

• Type: Bug
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 5.5.1
• Fix Version/s: 5.6.0
• Component/s: Broker
• Labels: concurrency

Environment

Darwin phillip.local 9.8.0 Darwin Kernel Version 9.8.0: Wed Jul 15 16:55:01 PDT 2009; root:xnu-1228.15.4~1/RELEASE_I386 i386 i386

• Assignee: Timothy A. Bish
• Reporter: Phillip Henry
• Created: 21/Feb/12 23:13
• Updated: 05/Mar/12 22:09
• Resolved: 05/Mar/12 22:09

Description

org.apache.activemq.broker.region.PrefetchSubscription.prefetchExtension is changed while guarded by a mutex on this (PrefetchSubscription) in PrefetchSubscription.pullMessage(...) and PrefetchSubscription.dispatchLock in PrefetchSubscription.acknowledge(...).

This can lead to the corruption of the prefetchExtension variable (eg, prefetchExtension++ in pullMessage() is not an atomic operation so prefetchExtension may change in acknowledge() mid-way through this operation).