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.windowing;
  
  /**
   * An eviction policy that evicts events based on time duration taking
   * watermark time and event lag into account.
   */
  public class WatermarkTimeEvictionPolicy<T> extends TimeEvictionPolicy<T> {
      private final int lag;
  
      /**
       * Constructs a WatermarkTimeEvictionPolicy that evicts events older
       * than the given window length in millis.
       *
       * @param windowLength the window length in milliseconds
       */
      public WatermarkTimeEvictionPolicy(int windowLength) {
          this(windowLength, Integer.MAX_VALUE);
      }
  
      /**
       * Constructs a WatermarkTimeEvictionPolicy that evicts events older
       * than the given window length in millis. The lag parameter
       * can be used in the case of event based ts to break the queue
       * scan early.
       *
       * @param windowLength the window length in milliseconds
       * @param lag          the max event lag in milliseconds
       */
      public WatermarkTimeEvictionPolicy(int windowLength, int lag) {
          super(windowLength);
          referenceTime = 0L;
          this.lag = lag;
      }
  
      /**
       * {@inheritDoc}
       * <p/>
       * Keeps events with future ts in the queue for processing in the next
       * window. If the ts difference is more than the lag, stops scanning
       * the queue for the current window.
       */
      @Override
      public Action evict(Event<T> event) {
          long diff = referenceTime - event.getTimestamp();
          if (diff < -lag) {
              return Action.STOP;
          } else if (diff < 0) {
              return Action.KEEP;
          } else {
              return super.evict(event);
          }
      }
  
      @Override
      public String toString() {
          return "WatermarkTimeEvictionPolicy{" +
                  "lag=" + lag +
                  "} " + super.toString();
      }
  }
  