[AMQ-3161] Race condition in ActiveMQ Journal Checkpoint worker thread cleanup leads to multiple running instances

• Type: Bug
• Status: Resolved
• Priority: Critical
• Resolution: Fixed
• Affects Version/s: 5.4.2
• Fix Version/s: 5.5.0
• Component/s: Message Store

Environment

CentOS 5.2

• Patch Info: Patch Available
• Assignee: Gary Tully
• Reporter: Craig Condit
• Created: 25/Jan/11 22:55
• Updated: 26/Jan/11 13:32
• Resolved: 26/Jan/11 13:32

Description

If the ActiveMQ Journal Checkpoint worker thread dies for any reason, any updates to KahaDB trigger the thread to be restarted. Unfortunately, there is a race condition between the Thread.isAlive() check and the restart of the thread, potentially leading to multiple instances of the thread being spawned. We have observed in a busy environment as many as 8-10 instances of this thread, all waking up every 5 seconds to perform database checkpoints, bringing throughput on the broker to a halt.

The attached patch adds a lock around access to creation/destruction of this thread and prevents a second instance from being launched inadvertently.

Issue Links

• relates to: AMQ-3160 ConcurrentModificationException in ActiveMQ Journal Checkpoint Worker