001/**
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements.  See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License.  You may obtain a copy of the License at
008 *
009 *      http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 */
017package org.apache.activemq.broker.region.policy;
018
019import java.util.Iterator;
020import java.util.List;
021import org.apache.activemq.broker.region.MessageReference;
022import org.apache.activemq.broker.region.Subscription;
023import org.apache.activemq.filter.MessageEvaluationContext;
024import org.slf4j.Logger;
025import org.slf4j.LoggerFactory;
026
027/**
028 * Simple dispatch policy that sends a message to every subscription that
029 * matches the message.
030 * 
031 * @org.apache.xbean.XBean
032 * 
033 */
034public class RoundRobinDispatchPolicy implements DispatchPolicy {
035    static final Logger LOG = LoggerFactory.getLogger(RoundRobinDispatchPolicy.class);
036
037    /**
038     * @param node
039     * @param msgContext
040     * @param consumers
041     * @return true if dispatched
042     * @throws Exception
043     * @see org.apache.activemq.broker.region.policy.DispatchPolicy#dispatch(org.apache.activemq.broker.region.MessageReference,
044     *      org.apache.activemq.filter.MessageEvaluationContext, java.util.List)
045     */
046    public boolean dispatch(MessageReference node,
047            MessageEvaluationContext msgContext, List<Subscription> consumers)
048            throws Exception {
049        int count = 0;
050
051        Subscription firstMatchingConsumer = null;
052        synchronized (consumers) {
053            for (Iterator<Subscription> iter = consumers.iterator(); iter
054                    .hasNext();) {
055                Subscription sub = iter.next();
056
057                // Only dispatch to interested subscriptions
058                if (!sub.matches(node, msgContext)) {
059                    sub.unmatched(node);
060                    continue;
061                }
062
063                if (firstMatchingConsumer == null) {
064                    firstMatchingConsumer = sub;
065                }
066
067                sub.add(node);
068                count++;
069            }
070
071            if (firstMatchingConsumer != null) {
072                // Rotate the consumer list.
073                try {
074                    consumers.remove(firstMatchingConsumer);
075                    consumers.add(firstMatchingConsumer);
076                } catch (Throwable bestEffort) {
077                }
078            }
079        }
080        return count > 0;
081    }
082}