001/*
002 * Licensed to the Apache Software Foundation (ASF) under one
003 * or more contributor license agreements.  See the NOTICE file
004 * distributed with this work for additional information
005 * regarding copyright ownership.  The ASF licenses this file
006 * to you under the Apache License, Version 2.0 (the
007 * "License"); you may not use this file except in compliance
008 * with the License.  You may obtain a copy of the License at
009 *
010 *   http://www.apache.org/licenses/LICENSE-2.0
011 *
012 * Unless required by applicable law or agreed to in writing,
013 * software distributed under the License is distributed on an
014 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
015 * KIND, either express or implied.  See the License for the
016 * specific language governing permissions and limitations
017 * under the License.
018 */
019package org.apache.reef.runtime.yarn.driver.restart;
020
021import org.apache.reef.annotations.audience.Private;
022import org.apache.reef.util.CloseableIterable;
023
024import java.io.IOException;
025
026/**
027 * The Evaluator log reader/writer that reads from and writes to the Hadoop DFS.
028 * Currently supports regular append and append by overwrite.
029 */
030@Private
031public interface DFSEvaluatorLogReaderWriter extends AutoCloseable {
032
033  /**
034   * Writes a formatted entry (addition or removal) for an Evaluator ID into the DFS evaluator log.
035   * @param formattedEntry The formatted entry (entry with evaluator ID and addition/removal information)
036   * @throws IOException
037   */
038  void writeToEvaluatorLog(final String formattedEntry) throws IOException;
039
040  /**
041   * Reads a formatted entry (addition or removal) from the DFS evaluator log.
042   * @return the formatted entry.
043   * @throws IOException
044   */
045  CloseableIterable<String> readFromEvaluatorLog() throws IOException;
046}