content: /**
   * Licensed to the Apache Software Foundation (ASF) under one or more
   * contributor license agreements.  See the NOTICE file distributed with
   * this work for additional information regarding copyright ownership.
   * The ASF licenses this file to You under the Apache License, Version 2.0
   * (the "License"); you may not use this file except in compliance with
   * the License.  You may obtain a copy of the License at
   *
   *      http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  package org.apache.activemq.broker.region.policy;
  
  import java.util.ArrayList;
  import java.util.Collections;
  import java.util.Iterator;
  import java.util.LinkedList;
  import java.util.List;
  import org.apache.activemq.broker.Broker;
  import org.apache.activemq.broker.ConnectionContext;
  import org.apache.activemq.broker.region.MessageReference;
  import org.apache.activemq.broker.region.SubscriptionRecovery;
  import org.apache.activemq.broker.region.Topic;
  import org.apache.activemq.command.ActiveMQDestination;
  import org.apache.activemq.command.Message;
  import org.apache.activemq.filter.DestinationFilter;
  import org.apache.activemq.thread.Scheduler;
  
  /**
   * This implementation of {@link SubscriptionRecoveryPolicy} will keep a timed
   * buffer of messages around in memory and use that to recover new
   * subscriptions.
   * 
   * @org.apache.xbean.XBean
   * 
   */
  public class TimedSubscriptionRecoveryPolicy implements SubscriptionRecoveryPolicy {
  
      private static final int GC_INTERVAL = 1000;
      private Scheduler scheduler;
      
      // TODO: need to get a better synchronized linked list that has little
      // contention between enqueuing and dequeuing
      private final List<TimestampWrapper> buffer = Collections.synchronizedList(new LinkedList<TimestampWrapper>());
      private volatile long lastGCRun = System.currentTimeMillis();
  
      private long recoverDuration = 60 * 1000; // Buffer for 1 min.
  
      static class TimestampWrapper {
          public MessageReference message;
          public long timestamp;
  
          public TimestampWrapper(MessageReference message, long timestamp) {
              this.message = message;
              this.timestamp = timestamp;
          }
      }
  
      private final Runnable gcTask = new Runnable() {
          public void run() {
              gc();
          }
      };
  
      public SubscriptionRecoveryPolicy copy() {
          TimedSubscriptionRecoveryPolicy rc = new TimedSubscriptionRecoveryPolicy();
          rc.setRecoverDuration(recoverDuration);
          return rc;
      }
  
      public boolean add(ConnectionContext context, MessageReference message) throws Exception {
          buffer.add(new TimestampWrapper(message, lastGCRun));
          return true;
      }
  
      public void recover(ConnectionContext context, Topic topic, SubscriptionRecovery sub) throws Exception {
          // Re-dispatch the messages from the buffer.
          ArrayList<TimestampWrapper> copy = new ArrayList<TimestampWrapper>(buffer);
          if (!copy.isEmpty()) {
              for (Iterator<TimestampWrapper> iter = copy.iterator(); iter.hasNext();) {
                  TimestampWrapper timestampWrapper = iter.next();
                  MessageReference message = timestampWrapper.message;
                  sub.addRecoveredMessage(context, message);
              }
          }
      }
      
      public void setBroker(Broker broker) {  
          this.scheduler = broker.getScheduler();
      }
  
      public void start() throws Exception {
          scheduler.executePeriodically(gcTask, GC_INTERVAL);
      }
  
      public void stop() throws Exception {
          scheduler.cancel(gcTask);
      }
      
  
      public void gc() {
          lastGCRun = System.currentTimeMillis();
          while (buffer.size() > 0) {
              TimestampWrapper timestampWrapper = buffer.get(0);
              if (lastGCRun > timestampWrapper.timestamp + recoverDuration) {
                  // GC it.
                  buffer.remove(0);
              } else {
                  break;
              }
          }
      }
  
      public long getRecoverDuration() {
          return recoverDuration;
      }
  
      public void setRecoverDuration(long recoverDuration) {
          this.recoverDuration = recoverDuration;
      }
  
      public Message[] browse(ActiveMQDestination destination) throws Exception {
          List<Message> result = new ArrayList<Message>();
          ArrayList<TimestampWrapper> copy = new ArrayList<TimestampWrapper>(buffer);
          DestinationFilter filter = DestinationFilter.parseFilter(destination);
          for (Iterator<TimestampWrapper> iter = copy.iterator(); iter.hasNext();) {
              TimestampWrapper timestampWrapper = iter.next();
              MessageReference ref = timestampWrapper.message;
              Message message = ref.getMessage();
              if (filter.matches(message.getDestination())) {
                  result.add(message);
              }
          }
          return result.toArray(new Message[result.size()]);
      }
  
  }
  