/*
 * 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.runners.dataflow.worker.util.common.worker;

import java.io.Closeable;
import javax.annotation.Nullable;
import javax.annotation.concurrent.NotThreadSafe;
import org.apache.beam.sdk.util.common.Reiterator;

/**
 * ShuffleEntryReader provides an interface for reading key/value entries from a shuffle dataset.
 */
@NotThreadSafe
public interface ShuffleEntryReader extends Closeable {
  /**
   * Returns an iterator that reads a range of entries from a shuffle dataset.
   *
   * @param startPosition encodes the initial key from where to read. This parameter may be null,
   *     indicating that the read should start with the first key in the dataset.
   * @param endPosition encodes the key "just past" the end of the range to be read; keys up to
   *     endPosition will be returned, but keys equal to or greater than endPosition will not. This
   *     parameter may be null, indicating that the read should end just past the last key in the
   *     dataset (that is, the last key in the dataset will be included in the read, as long as that
   *     key is greater than or equal to startPosition).
   * @return a {@link Reiterator} over the requested range of entries.
   */
  public Reiterator<ShuffleEntry> read(
      @Nullable ShufflePosition startPosition, @Nullable ShufflePosition endPosition);
}
