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;
  
  import java.util.ArrayList;
  import java.util.LinkedList;
  import java.util.List;
  
  import org.apache.activemq.command.MessageDispatch;
  
  public class SimplePriorityMessageDispatchChannel implements MessageDispatchChannel {
      private static final Integer MAX_PRIORITY = 10;
      private final Object mutex = new Object();
      private final LinkedList<MessageDispatch>[] lists;
      private boolean closed;
      private boolean running;
      private int size = 0;
  
      @SuppressWarnings("unchecked")
      public SimplePriorityMessageDispatchChannel() {
          this.lists = new LinkedList[MAX_PRIORITY];
          for (int i = 0; i < MAX_PRIORITY; i++) {
              lists[i] = new LinkedList<MessageDispatch>();
          }
      }
  
      /*
       * (non-Javadoc)
       *
       * @see org.apache.activemq.MessageDispatchChannelI#enqueue(org.apache.activemq.command.MessageDispatch)
       */
      @Override
      public void enqueue(MessageDispatch message) {
          synchronized (mutex) {
              getList(message).addLast(message);
              this.size++;
              mutex.notify();
          }
      }
  
      /*
       * (non-Javadoc)
       *
       * @see org.apache.activemq.MessageDispatchChannelI#enqueueFirst(org.apache.activemq.command.MessageDispatch)
       */
      @Override
      public void enqueueFirst(MessageDispatch message) {
          synchronized (mutex) {
              getList(message).addFirst(message);
              this.size++;
              mutex.notify();
          }
      }
  
      /*
       * (non-Javadoc)
       *
       * @see org.apache.activemq.MessageDispatchChannelI#isEmpty()
       */
      @Override
      public boolean isEmpty() {
          return this.size == 0;
      }
  
      /*
       * (non-Javadoc)
       *
       * @see org.apache.activemq.MessageDispatchChannelI#dequeue(long)
       */
      @Override
      public MessageDispatch dequeue(long timeout) throws InterruptedException {
          synchronized (mutex) {
              // Wait until the consumer is ready to deliver messages.
              while (timeout != 0 && !closed && (isEmpty() || !running)) {
                  if (timeout == -1) {
                      mutex.wait();
                  } else {
                      mutex.wait(timeout);
                      break;
                  }
              }
              if (closed || !running || isEmpty()) {
                  return null;
              }
              return removeFirst();
          }
      }
  
      /*
       * (non-Javadoc)
       *
       * @see org.apache.activemq.MessageDispatchChannelI#dequeueNoWait()
       */
      @Override
      public MessageDispatch dequeueNoWait() {
          synchronized (mutex) {
              if (closed || !running || isEmpty()) {
                  return null;
              }
              return removeFirst();
          }
      }
  
      /*
       * (non-Javadoc)
       *
       * @see org.apache.activemq.MessageDispatchChannelI#peek()
       */
      @Override
      public MessageDispatch peek() {
          synchronized (mutex) {
              if (closed || !running || isEmpty()) {
                  return null;
              }
              return getFirst();
          }
      }
  
      /*
       * (non-Javadoc)
       *
       * @see org.apache.activemq.MessageDispatchChannelI#start()
       */
      @Override
      public void start() {
          synchronized (mutex) {
              running = true;
              mutex.notifyAll();
          }
      }
  
      /*
       * (non-Javadoc)
       *
       * @see org.apache.activemq.MessageDispatchChannelI#stop()
       */
      @Override
      public void stop() {
          synchronized (mutex) {
              running = false;
              mutex.notifyAll();
          }
      }
  
      /*
       * (non-Javadoc)
       *
       * @see org.apache.activemq.MessageDispatchChannelI#close()
       */
      @Override
      public void close() {
          synchronized (mutex) {
              if (!closed) {
                  running = false;
                  closed = true;
              }
              mutex.notifyAll();
          }
      }
  
      /*
       * (non-Javadoc)
       *
       * @see org.apache.activemq.MessageDispatchChannelI#clear()
       */
      @Override
      public void clear() {
          synchronized (mutex) {
              for (int i = 0; i < MAX_PRIORITY; i++) {
                  lists[i].clear();
              }
              this.size = 0;
          }
      }
  
      /*
       * (non-Javadoc)
       *
       * @see org.apache.activemq.MessageDispatchChannelI#isClosed()
       */
      @Override
      public boolean isClosed() {
          return closed;
      }
  
      /*
       * (non-Javadoc)
       *
       * @see org.apache.activemq.MessageDispatchChannelI#size()
       */
      @Override
      public int size() {
          synchronized (mutex) {
              return this.size;
          }
      }
  
      /*
       * (non-Javadoc)
       *
       * @see org.apache.activemq.MessageDispatchChannelI#getMutex()
       */
      @Override
      public Object getMutex() {
          return mutex;
      }
  
      /*
       * (non-Javadoc)
       *
       * @see org.apache.activemq.MessageDispatchChannelI#isRunning()
       */
      @Override
      public boolean isRunning() {
          return running;
      }
  
      /*
       * (non-Javadoc)
       *
       * @see org.apache.activemq.MessageDispatchChannelI#removeAll()
       */
      @Override
      public List<MessageDispatch> removeAll() {
          synchronized (mutex) {
              ArrayList<MessageDispatch> result = new ArrayList<MessageDispatch>(size());
              for (int i = MAX_PRIORITY - 1; i >= 0; i--) {
                  List<MessageDispatch> list = lists[i];
                  result.addAll(list);
                  size -= list.size();
                  list.clear();
              }
              return result;
          }
      }
  
      @Override
      public String toString() {
          String result = "";
          for (int i = MAX_PRIORITY - 1; i >= 0; i--) {
              result += i + ":{" + lists[i].toString() + "}";
          }
          return result;
      }
  
      protected int getPriority(MessageDispatch message) {
          int priority = jakarta.jms.Message.DEFAULT_PRIORITY;
          if (message.getMessage() != null) {
              priority = Math.max(message.getMessage().getPriority(), 0);
              priority = Math.min(priority, 9);
          }
          return priority;
      }
  
      protected LinkedList<MessageDispatch> getList(MessageDispatch md) {
          return lists[getPriority(md)];
      }
  
      private final MessageDispatch removeFirst() {
          if (this.size > 0) {
              for (int i = MAX_PRIORITY - 1; i >= 0; i--) {
                  LinkedList<MessageDispatch> list = lists[i];
                  if (!list.isEmpty()) {
                      this.size--;
                      return list.removeFirst();
                  }
              }
          }
          return null;
      }
  
      private final MessageDispatch getFirst() {
          if (this.size > 0) {
              for (int i = MAX_PRIORITY - 1; i >= 0; i--) {
                  LinkedList<MessageDispatch> list = lists[i];
                  if (!list.isEmpty()) {
                      return list.getFirst();
                  }
              }
          }
          return null;
      }
  }
  