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;
024
025/**
026 * Simple dispatch policy that sends a message to every subscription that
027 * matches the message.
028 * 
029 * @org.apache.xbean.XBean
030 * 
031 */
032public class RoundRobinDispatchPolicy implements DispatchPolicy {
033
034    /**
035     * @param node
036     * @param msgContext
037     * @param consumers
038     * @return true if dispatched
039     * @throws Exception
040     * @see org.apache.activemq.broker.region.policy.DispatchPolicy#dispatch(org.apache.activemq.broker.region.MessageReference,
041     *      org.apache.activemq.filter.MessageEvaluationContext, java.util.List)
042     */
043    public boolean dispatch(MessageReference node,
044            MessageEvaluationContext msgContext, List<Subscription> consumers)
045            throws Exception {
046        int count = 0;
047
048        Subscription firstMatchingConsumer = null;
049        synchronized (consumers) {
050            for (Iterator<Subscription> iter = consumers.iterator(); iter
051                    .hasNext();) {
052                Subscription sub = iter.next();
053
054                // Only dispatch to interested subscriptions
055                if (!sub.matches(node, msgContext)) {
056                    sub.unmatched(node);
057                    continue;
058                }
059
060                if (firstMatchingConsumer == null) {
061                    firstMatchingConsumer = sub;
062                }
063
064                sub.add(node);
065                count++;
066            }
067
068            if (firstMatchingConsumer != null) {
069                // Rotate the consumer list.
070                try {
071                    consumers.remove(firstMatchingConsumer);
072                    consumers.add(firstMatchingConsumer);
073                } catch (Throwable bestEffort) {
074                }
075            }
076        }
077        return count > 0;
078    }
079}