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     */
017    package org.apache.activemq.broker.region.policy;
018    
019    import java.util.Iterator;
020    import java.util.List;
021    import org.apache.activemq.broker.region.MessageReference;
022    import org.apache.activemq.broker.region.Subscription;
023    import org.apache.activemq.filter.MessageEvaluationContext;
024    import org.slf4j.Logger;
025    import 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     */
034    public 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    }