Source code

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.io;
020
021import org.apache.reef.annotations.Unstable;
022import org.apache.reef.exception.evaluator.ServiceException;
023
024import java.util.Iterator;
025
026/**
027 * Spool files can be appended to, and can be scanned starting at the beginning.
028 * Random read and write access is not supported. Spool files are ephemeral; the
029 * space they use will be automatically reclaimed by REEF.
030 */
031@Unstable
032public interface Spool<T> extends Iterable<T>, Accumulable<T> {
033
034  /**
035   * Returns an Iterable over the spool file.
036   * <p>
037   * Depending on the implementation, this method may be called only once per
038   * Spool instance, or it may be called repeatedly. Similarly, with some Spool
039   * implementations, attempts to append to the SpoolFile after calling
040   * iterator() may fail fast with a ConcurrentModificationException.
041   *
042   * @return An Iterator over the SpoolFile, in the order data was inserted.
043   */
044  @Override
045  Iterator<T> iterator();
046
047  /**
048   * Returns an Accumulator for the spool file.
049   * <p>
050   * Depending on the implementation, this method may be called only once per
051   * Spool instance, or it may be called repeatedly. Similarly, with some Spool
052   * implementations, attempts to append to the SpoolFile after calling
053   * iterator() may fail fast with a ConcurrentModificationException.
054   *
055   * @throws ServiceException
056   */
057  @Override
058  Accumulator<T> accumulator() throws ServiceException;
059}