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;
  
  /**
   * Eviction policy tracks events and decides whether
   * an event should be evicted from the window or not.
   *
   * @param <T> the type of event that is tracked.
   */
  public interface EvictionPolicy<T> {
      /**
       * The action to be taken when {@link EvictionPolicy#evict(Event)} is invoked.
       */
      enum Action {
          /**
           * expire the event and remove it from the queue
           */
          EXPIRE,
          /**
           * process the event in the current window of events
           */
          PROCESS,
          /**
           * don't include in the current window but keep the event
           * in the queue for evaluating as a part of future windows
           */
          KEEP,
          /**
           * stop processing the queue, there cannot be anymore events
           * satisfying the eviction policy
           */
          STOP
      }
      /**
       * Decides if an event should be expired from the window, processed in the current
       * window or kept for later processing.
       *
       * @param event the input event
       * @return the {@link org.apache.storm.windowing.EvictionPolicy.Action} to be taken based on the input event
       */
      Action evict(Event<T> event);
  
      /**
       * Tracks the event to later decide whether
       * {@link EvictionPolicy#evict(Event)} should evict it or not.
       *
       * @param event the input event to be tracked
       */
      void track(Event<T> event);
  
      /**
       * Sets a context in the eviction policy that can be used while evicting the events.
       * E.g. For TimeEvictionPolicy, this could be used to set the reference timestamp.
       *
       * @param context
       */
      void setContext(Object context);
  }
  