[AMQNET-727] Thread sync error with MessageConsumer.pendingAck

• Type: Bug
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Affects Version/s: 1.8.0
• Component/s: OpenWire
• Assignee: Unassigned
• Reporter: Andy DeMaurice
• Created: 17/Aug/21 14:56
• Updated: 13/May/24 21:28

Description

pendingAck is accessed by multiple threads; in most places where it is written, it is done along with accessing deliveredMessages, so it is written within a lock(this.deliveredMessages) block.

However, this call stack shows where pendingAck gets assigned to a new MessageAck object, NOT within the lock... and it is subject to being overwritten by another thread (usually the other thread is in MessageConsumer.Acknowledge() :

 

Apache.NMS.ActiveMQ.MessageConsumer.AckLater(Apache.NMS.ActiveMQ.Commands.MessageDispatch, Apache.NMS.ActiveMQ.AckType)
Apache.NMS.ActiveMQ.MessageConsumer.AfterMessageIsConsumed(Apache.NMS.ActiveMQ.Commands.MessageDispatch, Boolean)
Apache.NMS.ActiveMQ.MessageConsumer.Dispatch(Apache.NMS.ActiveMQ.Commands.MessageDispatch)
Apache.NMS.ActiveMQ.SessionExecutor.Dispatch(Apache.NMS.ActiveMQ.Commands.MessageDispatch)
Apache.NMS.ActiveMQ.SessionExecutor.Iterate()
Apache.NMS.ActiveMQ.Threads.DedicatedTaskRunner.Run()

 

The usual symptom I see is a NullReferenceException in this section of code within AckLater; because pendingAck has been set to null by another thread:

 

if(oldPendingAck == null)

{    pendingAck.FirstMessageId = pendingAck.LastMessageId; }

else if(oldPendingAck.AckType == pendingAck.AckType)

{    pendingAck.FirstMessageId = oldPendingAck.FirstMessageId; }