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 com.alibaba.jstorm.window;
  
  import java.io.Serializable;
  import java.util.Collection;
  import java.util.concurrent.ScheduledFuture;
  
  /**
   * A {@code Trigger} determines when a pane of a window should be evaluated to emit the
   * results for that part of the window.
   *
   * @param <T> The type of elements on which this {@code Trigger} works.
   */
  public abstract class Trigger<T> implements Serializable {
  
      private static final long serialVersionUID = 1L;
  
      /**
       * Called for every element that gets added to a pane. The result of this will determine
       * whether the pane is evaluated to emit results.
       *
       * @param element   The element that arrived.
       * @param timestamp The timestamp of the element that arrived.
       * @param window    The window to which the element is being added.
       * @param ctx       A context object that can be used to register timer callbacks.
       */
      public abstract TriggerResult onElement(T element, long timestamp, TimeWindow window, TriggerContext ctx);
  
      // ------------------------------------------------------------------------
  
      /**
       * A context object that is given to {@link Trigger} methods to allow them to register timer
       * callbacks and deal with state.
       */
      public interface TriggerContext {
  
          /**
           * Get max lag time in ms
           */
          long getMaxLagMs();
  
          /**
           * Returns the current watermark time.
           */
          long getCurrentWatermark();
  
          /**
           * Get pending windows
           */
          Collection<TimeWindow> getPendingWindows();
  
          /**
           * Register a system time callback.
           *
           * @param time   the timestamp at which to trigger the timer
           * @param window the window to which current input belongs
           */
          void registerProcessingTimeTimer(long time, TimeWindow window);
  
          /**
           * Register an event-time callback.
           *
           * @param time   the timestamp at which to trigger the timer
           * @param window the window to which current input belongs
           */
          void registerEventTimeTimer(long time, TimeWindow window);
  
          /**
           * Delete the processing time trigger for the given time.
           */
          ScheduledFuture<?> deleteProcessingTimeTimer(TimeWindow window);
  
          /**
           * Delete the event-time trigger for the given time.
           */
          ScheduledFuture<?> deleteEventTimeTimer(TimeWindow window);
  
      }
  
  }
  