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 * Dispatch policy that causes every subscription to see messages in the same
027 * order.
028 * 
029 * @org.apache.xbean.XBean
030 * 
031 */
032public class StrictOrderDispatchPolicy 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, MessageEvaluationContext msgContext, List consumers) throws Exception {
044        // Big synch here so that only 1 message gets dispatched at a time.
045        // Ensures
046        // Everyone sees the same order.
047        synchronized (consumers) {
048            int count = 0;
049            for (Iterator iter = consumers.iterator(); iter.hasNext();) {
050                Subscription sub = (Subscription)iter.next();
051
052                // Only dispatch to interested subscriptions
053                if (!sub.matches(node, msgContext)) {
054                    sub.unmatched(node);
055                    continue;
056                }
057
058                sub.add(node);
059                count++;
060            }
061            return count > 0;
062        }
063    }
064
065}