IndexOutOfBoundsException in DirectMessageListenerContainer#adjustConsumers

[davidbilge]

Our system that uses spring-amqp constantly logs this stacktrace:

java.lang.IndexOutOfBoundsException: Index: 2, Size: 2
        at java.util.LinkedList.checkElementIndex(LinkedList.java:555)
        at java.util.LinkedList.remove(LinkedList.java:525)
        at org.springframework.amqp.rabbit.listener.DirectMessageListenerContainer.adjustConsumers(DirectMessageListenerContainer.java:289)
        at org.springframework.amqp.rabbit.listener.DirectMessageListenerContainer.setConsumersPerQueue(DirectMessageListenerContainer.java:152)
        at org.springframework.amqp.rabbit.listener.DirectReplyToMessageListenerContainer.processMonitorTask(DirectReplyToMessageListenerContainer.java:136)
        at org.springframework.amqp.rabbit.listener.DirectMessageListenerContainer.lambda$actualStart$3(DirectMessageListenerContainer.java:429)
        at org.springframework.scheduling.support.DelegatingErrorHandlingRunnable.run(DelegatingErrorHandlingRunnable.java:54)
        at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
        at java.util.concurrent.FutureTask.runAndReset(FutureTask.java:308)
        at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$301(ScheduledThreadPoolExecutor.java:180)
        at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:294)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
        at java.lang.Thread.run(Thread.java:748)

Looking at the adjustConsumers method in DirectMessageListenerContainer it seems like this will always happen if newCount < consumerList.size() - 1, i.e. if the number of consumers is to be reduced by more than one.

One solution might be to replace

SimpleConsumer consumer = consumerList.remove(i);

with

SimpleConsumer consumer = consumerList.remove(0);

if it does not matter which consumers will be removed.

This affects spring-rabbit 2.0.1.RELEASE.

[artembilan]

Ha! Sure! That's definitely good catch 😄

Indeed, when we call consumerList.remove(8) on the list of 10, the list becomes as 9 of the size. So, the next consumerList.remove(9) brings us exactly that IndexOutOfBoundsException.

I have just modified DirectMessageListenerContainerIntegrationTests.testAddRemoveConsumers() to adjust from 4 to 1 consumer and get exactly the same exception:

java.lang.IndexOutOfBoundsException: Index: 3, Size: 2

	at java.util.LinkedList.checkElementIndex(LinkedList.java:555)
	at java.util.LinkedList.remove(LinkedList.java:525)
	at org.springframework.amqp.rabbit.listener.DirectMessageListenerContainer.adjustConsumers(DirectMessageListenerContainer.java:289)
	at org.springframework.amqp.rabbit.listener.DirectMessageListenerContainer.setConsumersPerQueue(DirectMessageListenerContainer.java:152)
	at org.springframework.amqp.rabbit.listener.DirectMessageListenerContainerIntegrationTests.testAddRemoveConsumers(DirectMessageListenerContainerIntegrationTests.java:296)

[davidbilge]

Are there any plans on the next bugfix release? Thinking about using a patched jar for our system but it would be nice to be able to avoid this.

[garyrussell]

It's currently scheduled for next Wednesday; just in time for the Boot 2.0 release candidate 1. We could possibly pull it forward a day or two if necessary.

[davidbilge]

Next wednesday sounds good to me. Thanks for the information!