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, software
013 * distributed under the License is distributed on an "AS IS" BASIS,
014 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
015 * See the License for the specific language governing permissions and
016 * limitations under the License.
017 */
018package org.apache.hadoop.hdfs.server.datanode.fsdataset;
019
020import java.io.Closeable;
021import java.io.IOException;
022
023/**
024 * This is the interface for holding reference count as AutoClosable resource.
025 * It increases the reference count by one in the constructor, and decreases
026 * the reference count by one in {@link #close()}.
027 *
028 * <pre>
029 *  {@code
030 *    try (FsVolumeReference ref = volume.obtainReference()) {
031 *      // Do IOs on the volume
032 *      volume.createRwb(...);
033 *      ...
034 *    }
035 *  }
036 * </pre>
037 */
038public interface FsVolumeReference extends Closeable {
039  /**
040   * Descrese the reference count of the volume.
041   * @throws IOException it never throws IOException.
042   */
043  @Override
044  public void close() throws IOException;
045
046  /** Returns the underlying volume object */
047  public FsVolumeSpi getVolume();
048}