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 backtype.storm.utils;
  
  import java.util.ArrayList;
  import java.util.HashMap;
  import java.util.LinkedList;
  import java.util.List;
  import java.util.Map;
  import java.util.Queue;
  import java.util.concurrent.Semaphore;
  
  public class KeyedRoundRobinQueue<V> {
      private final Object _lock = new Object();
      private Semaphore _size = new Semaphore(0);
      private Map<Object, Queue<V>> _queues = new HashMap<>();
      private List<Object> _keyOrder = new ArrayList<>();
      private int _currIndex = 0;
  
      public void add(Object key, V val) {
          synchronized (_lock) {
              Queue<V> queue = _queues.get(key);
              if (queue == null) {
                  queue = new LinkedList<>();
                  _queues.put(key, queue);
                  _keyOrder.add(key);
              }
              queue.add(val);
          }
          _size.release();
      }
  
      public V take() throws InterruptedException {
          _size.acquire();
          synchronized (_lock) {
              Object key = _keyOrder.get(_currIndex);
              Queue<V> queue = _queues.get(key);
              V ret = queue.remove();
              if (queue.isEmpty()) {
                  _keyOrder.remove(_currIndex);
                  _queues.remove(key);
                  if (_keyOrder.size() == 0) {
                      _currIndex = 0;
                  } else {
                      _currIndex = _currIndex % _keyOrder.size();
                  }
              } else {
                  _currIndex = (_currIndex + 1) % _keyOrder.size();
              }
              return ret;
          }
      }
  }
  