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From "Piero Cangianiello (JIRA)" <j...@apache.org>
Subject [jira] [Created] (CAMEL-10229) Race condition when stopping context with autoack=false
Date Tue, 09 Aug 2016 15:48:20 GMT
Piero Cangianiello created CAMEL-10229:
------------------------------------------

             Summary: Race condition when stopping context with autoack=false
                 Key: CAMEL-10229
                 URL: https://issues.apache.org/jira/browse/CAMEL-10229
             Project: Camel
          Issue Type: Bug
          Components: camel-rabbitmq
    Affects Versions: 2.17.3
            Reporter: Piero Cangianiello


Run the following code and hit enter while one message is in unacked state (see RabbitMQ console):

{code:java}
public static void main(String[] args) throws Exception {
	CamelContext context = new DefaultCamelContext();
	createEndpoints(context);

	context.addRoutes(new RouteBuilder() {
		@Override
		public void configure() {
			from("rabbitmq://localhost/?queue=sourceQueue&skipExchangeDeclare=true&skipQueueDeclare=true&autoAck=false&prefetchEnabled=true&prefetchCount=1")
					.delayer(5000)
					.setHeader("rabbitmq.ROUTING_KEY", constant("destinationQueue"))
					.to("rabbitmq://localhost/?skipExchangeDeclare=true&skipQueueDeclare=true&autoAck=false")
					.routeId("myRoute");
		}
	});
	context.start();
	new BufferedReader(new InputStreamReader(System.in)).readLine();
	context.stop();
}
{code}

you get the following exception:

{noformat}
com.rabbitmq.client.impl.DefaultExceptionHandler: Consumer org.apache.camel.component.rabbitmq.RabbitConsumer@4c57777e
(amq.ctag-dWpQw46flmamv0dM_Fa_Qg) method handleDelivery for channel AMQChannel(amqp://rabbit_user@127.0.0.1:5672/,1)
threw an exception for channel AMQChannel(amqp://rabbit_user@127.0.0.1:5672/,1):
com.rabbitmq.client.AlreadyClosedException: channel is already closed due to clean channel
shutdown; protocol method: #method<channel.close>(reply-code=200, reply-text=OK, class-id=0,
method-id=0)
	at com.rabbitmq.client.impl.AMQChannel.ensureIsOpen(AMQChannel.java:195)
	at com.rabbitmq.client.impl.AMQChannel.transmit(AMQChannel.java:309)
	at com.rabbitmq.client.impl.AMQChannel.transmit(AMQChannel.java:303)
	at com.rabbitmq.client.impl.ChannelN.basicAck(ChannelN.java:1043)
	at org.apache.camel.component.rabbitmq.RabbitConsumer.handleDelivery(RabbitConsumer.java:108)
	at com.rabbitmq.client.impl.ConsumerDispatcher$5.run(ConsumerDispatcher.java:144)
	at com.rabbitmq.client.impl.ConsumerWorkService$WorkPoolRunnable.run(ConsumerWorkService.java:99)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
	at java.lang.Thread.run(Thread.java:745)
{noformat}

I think that this is caused by a race condition between the main thread that runs channel.close();
immediately after channel.basicCancel(tag); (see org.apache.camel.component.rabbitmq.RabbitConsumer)
without waiting the channel.basicAck(deliveryTag, false); in handleDelivery().

Another bad side effect is that you'll find a duplicate of a message on the destinationQueue.
For example if you have 10 initial messages in sourceQueue and you hit enter while it's processing
the third one, you'll get 7 messages in sourceQueue and 4 messages in destinationQueue.

The correct behaviour should be the following:
1) Stop consumer: channel.basicCancel(tag)
2) Wait if there is a running consumer
3) The consumer acks the previous message
4) Close the channel



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