[AMQ-5198] MessageConsumer and Producer are not thread safe

• Type: Bug
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 5.9.0
• Fix Version/s: 5.10.1, 5.11.0
• Assignee: Unassigned
• Reporter: Enrico Musuruana
• Created: 22/May/14 09:24
• Updated: 25/Sep/15 19:15
• Resolved: 18/Jul/14 14:13

Description

We currently have an object that acts both as a consumer and as a producer over the same queue.

Lazy initialization of the scheduler is not 100% thread safe when a consumer and a producer are created sharing the same connection.

We encountered the following sporadic NPE when a rollback() is invoked:
Caused by: java.lang.NullPointerException
at org.apache.activemq.thread.Scheduler.executeAfterDelay(Scheduler.java:64)
at org.apache.activemq.ActiveMQMessageConsumer.rollback(ActiveMQMessageConsumer.java:1278)
at org.apache.activemq.ActiveMQMessageConsumer$5.afterRollback(ActiveMQMessageConsumer.java:1054)
at org.apache.activemq.TransactionContext.afterRollback(TransactionContext.java:157)
... 11 more

We believe that the lazy initialized getScheduler() is open for a race condition when a publish and rollback are happening concurrently.

try

{ result = scheduler = new Scheduler("ActiveMQConnection["+info.getConnectionId().getValue()+"] Scheduler"); scheduler.start(); }

catch(Exception e)

{ throw JMSExceptionSupport.create(e); }

The suggested fix is to simply invoke the start within the constructor of the Scheduler class.