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 org.apache.beam.sdk.state;
  
  import org.apache.beam.sdk.annotations.Internal;
  import org.apache.beam.sdk.transforms.windowing.TimestampCombiner;
  import org.joda.time.Instant;
  
  /**
   * <b><i>For internal use only; no backwards-compatibility guarantees.</i></b>
   *
   * <p>A {@link State} accepting and aggregating timestamps according to a {@link TimestampCombiner},
   * holding the output watermark to the resulting timestamp.
   */
  @Internal
  public interface WatermarkHoldState extends GroupingState<Instant, Instant> {
    /**
     * Return the {@link TimestampCombiner} which will be used to determine a watermark hold time
     * given an element timestamp, and to combine watermarks from windows which are about to be
     * merged.
     */
    TimestampCombiner getTimestampCombiner();
  
    @Override
    WatermarkHoldState readLater();
  }
  