Mutlitple Exclusive Consumers: It is currently not possible to always ensure
that a new exclusive consumer replaces any existing one
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Key: AMQ-3218
URL: https://issues.apache.org/jira/browse/AMQ-3218
Project: ActiveMQ
Issue Type: Improvement
Components: Broker
Affects Versions: 5.4.2
Reporter: Rob Stocks
Priority: Minor
The following is a proposed small change to
org.apache.activemq.broker.region.Queue addSubscription() method:
If the new consumer is exclusive and has the maximum priority (127), replace
the existing exclusive consumer even if it also has a priority of 127 as
follows (line 385 in version 5.4.2 source):
if (exclusiveConsumer == null) {
exclusiveConsumer = sub;
} else if (sub.getConsumerInfo().getPriority() == Byte.MAX_VALUE) {
exclusiveConsumer = sub;
} else if (sub.getConsumerInfo().getPriority() >
exclusiveConsumer.getConsumerInfo().getPriority()) {
exclusiveConsumer = sub;
}
This allows new consumers to always replace any existing exclusive consumer
(but preserves behaviour in all but 1 unusual case). There may be a better way
of donig this (e.g. adding an ExclusiveMode property to ConsumerInfo with
values such as 'PRIORITY', 'NEWEST' which determines whether the priority is
checked or the latest exclusive consumer replaces an y existing one) but the
above is a quick fix for this problem.
The reason, we have added this to our implementation is that we have an
application that uses a STOMP client on Windows Mobile to post messages to a
queue and wait for the reply. However, when the device goes to sleep, the TCP
socket remains open on the server even though it is forceably closed on wake-up
on the client. The client then creates a new connection and we end up with
multiple consumers on our queue with new messages being distributed between
them. If we turn on exclusivity, the original consumer gets all the messages
which doesn't help (it actually makes it worse).
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