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.ArrayList;
020    import java.util.Collections;
021    import java.util.Iterator;
022    import java.util.LinkedList;
023    import java.util.List;
024    import org.apache.activemq.broker.Broker;
025    import org.apache.activemq.broker.ConnectionContext;
026    import org.apache.activemq.broker.region.MessageReference;
027    import org.apache.activemq.broker.region.SubscriptionRecovery;
028    import org.apache.activemq.broker.region.Topic;
029    import org.apache.activemq.command.ActiveMQDestination;
030    import org.apache.activemq.command.Message;
031    import org.apache.activemq.filter.DestinationFilter;
032    import org.apache.activemq.thread.Scheduler;
033    
034    /**
035     * This implementation of {@link SubscriptionRecoveryPolicy} will keep a timed
036     * buffer of messages around in memory and use that to recover new
037     * subscriptions.
038     * 
039     * @org.apache.xbean.XBean
040     * 
041     */
042    public class TimedSubscriptionRecoveryPolicy implements SubscriptionRecoveryPolicy {
043    
044        private static final int GC_INTERVAL = 1000;
045        private Scheduler scheduler;
046        
047        // TODO: need to get a better synchronized linked list that has little
048        // contention between enqueuing and dequeuing
049        private final List<TimestampWrapper> buffer = Collections.synchronizedList(new LinkedList<TimestampWrapper>());
050        private volatile long lastGCRun = System.currentTimeMillis();
051    
052        private long recoverDuration = 60 * 1000; // Buffer for 1 min.
053    
054        static class TimestampWrapper {
055            public MessageReference message;
056            public long timestamp;
057    
058            public TimestampWrapper(MessageReference message, long timestamp) {
059                this.message = message;
060                this.timestamp = timestamp;
061            }
062        }
063    
064        private final Runnable gcTask = new Runnable() {
065            public void run() {
066                gc();
067            }
068        };
069    
070        public SubscriptionRecoveryPolicy copy() {
071            TimedSubscriptionRecoveryPolicy rc = new TimedSubscriptionRecoveryPolicy();
072            rc.setRecoverDuration(recoverDuration);
073            return rc;
074        }
075    
076        public boolean add(ConnectionContext context, MessageReference message) throws Exception {
077            buffer.add(new TimestampWrapper(message, lastGCRun));
078            return true;
079        }
080    
081        public void recover(ConnectionContext context, Topic topic, SubscriptionRecovery sub) throws Exception {
082            // Re-dispatch the messages from the buffer.
083            ArrayList<TimestampWrapper> copy = new ArrayList<TimestampWrapper>(buffer);
084            if (!copy.isEmpty()) {
085                for (Iterator<TimestampWrapper> iter = copy.iterator(); iter.hasNext();) {
086                    TimestampWrapper timestampWrapper = iter.next();
087                    MessageReference message = timestampWrapper.message;
088                    sub.addRecoveredMessage(context, message);
089                }
090            }
091        }
092        
093        public void setBroker(Broker broker) {  
094            this.scheduler = broker.getScheduler();
095        }
096    
097        public void start() throws Exception {
098            scheduler.executePeriodically(gcTask, GC_INTERVAL);
099        }
100    
101        public void stop() throws Exception {
102            scheduler.cancel(gcTask);
103        }
104        
105    
106        public void gc() {
107            lastGCRun = System.currentTimeMillis();
108            while (buffer.size() > 0) {
109                TimestampWrapper timestampWrapper = buffer.get(0);
110                if (lastGCRun > timestampWrapper.timestamp + recoverDuration) {
111                    // GC it.
112                    buffer.remove(0);
113                } else {
114                    break;
115                }
116            }
117        }
118    
119        public long getRecoverDuration() {
120            return recoverDuration;
121        }
122    
123        public void setRecoverDuration(long recoverDuration) {
124            this.recoverDuration = recoverDuration;
125        }
126    
127        public Message[] browse(ActiveMQDestination destination) throws Exception {
128            List<Message> result = new ArrayList<Message>();
129            ArrayList<TimestampWrapper> copy = new ArrayList<TimestampWrapper>(buffer);
130            DestinationFilter filter = DestinationFilter.parseFilter(destination);
131            for (Iterator<TimestampWrapper> iter = copy.iterator(); iter.hasNext();) {
132                TimestampWrapper timestampWrapper = iter.next();
133                MessageReference ref = timestampWrapper.message;
134                Message message = ref.getMessage();
135                if (filter.matches(message.getDestination())) {
136                    result.add(message);
137                }
138            }
139            return result.toArray(new Message[result.size()]);
140        }
141    
142    }