SpringSource/spring-amqp — pull request #66 by garyrussell (2012-08-06 21:02:22+00:00)
Title: AMQP-262 ConcurrentExecutionException

When a 'multiple' ack is received, we iterate over pending acks for
each listener in order to generate a discrete ack for each.

While this is synchronized on the entire pending acks map, addition
of a new pending ack can cause a ConcurrentModificationException.

sychnronize the put(); add a test to reproduce the issue and to
show the correction fixes the problem.