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;
  
  import java.util.concurrent.atomic.AtomicInteger;
  
  /**
   * An eviction policy that tracks event counts and can
   * evict based on a threshold count.
   *
   * @param <T> the type of event tracked by this policy.
   */
  public class CountEvictionPolicy<T> implements EvictionPolicy<T> {
      private final int threshold;
      protected final AtomicInteger currentCount;
  
      public CountEvictionPolicy(int count) {
          this.threshold = count;
          this.currentCount = new AtomicInteger();
      }
  
      @Override
      public Action evict(Event<T> event) {
          /*
           * atomically decrement the count if its greater than threshold and
           * return if the event should be evicted
           */
          while (true) {
              int curVal = currentCount.get();
              if (curVal > threshold) {
                  if (currentCount.compareAndSet(curVal, curVal - 1)) {
                      return Action.EXPIRE;
                  }
              } else {
                  break;
              }
          }
          return Action.PROCESS;
      }
  
      @Override
      public void track(Event<T> event) {
          if (!event.isWatermark()) {
              currentCount.incrementAndGet();
          }
      }
  
      @Override
      public void setContext(Object context) {
          // NOOP
      }
  
      @Override
      public String toString() {
          return "CountEvictionPolicy{" +
                  "threshold=" + threshold +
                  ", currentCount=" + currentCount +
                  '}';
      }
  }
  