| /** |
| * 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.hadoop.hdfs.util; |
| |
| import java.io.BufferedReader; |
| import java.io.File; |
| import java.io.FileInputStream; |
| import java.io.IOException; |
| import java.io.InputStreamReader; |
| |
| import org.apache.commons.logging.Log; |
| import org.apache.commons.logging.LogFactory; |
| import org.apache.hadoop.classification.InterfaceAudience; |
| import org.apache.hadoop.io.IOUtils; |
| |
| import com.google.common.base.Charsets; |
| |
| /** |
| * Class that represents a file on disk which persistently stores |
| * a single <code>long</code> value. The file is updated atomically |
| * and durably (i.e fsynced). |
| */ |
| @InterfaceAudience.Private |
| public class PersistentLongFile { |
| private static final Log LOG = LogFactory.getLog( |
| PersistentLongFile.class); |
| |
| private final File file; |
| private final long defaultVal; |
| |
| private long value; |
| private boolean loaded = false; |
| |
| public PersistentLongFile(File file, long defaultVal) { |
| this.file = file; |
| this.defaultVal = defaultVal; |
| } |
| |
| public long get() throws IOException { |
| if (!loaded) { |
| value = readFile(file, defaultVal); |
| loaded = true; |
| } |
| return value; |
| } |
| |
| public void set(long newVal) throws IOException { |
| if (value != newVal || !loaded) { |
| writeFile(file, newVal); |
| } |
| value = newVal; |
| loaded = true; |
| } |
| |
| /** |
| * Atomically write the given value to the given file, including fsyncing. |
| * |
| * @param file destination file |
| * @param val value to write |
| * @throws IOException if the file cannot be written |
| */ |
| public static void writeFile(File file, long val) throws IOException { |
| AtomicFileOutputStream fos = new AtomicFileOutputStream(file); |
| try { |
| fos.write(String.valueOf(val).getBytes(Charsets.UTF_8)); |
| fos.write('\n'); |
| fos.close(); |
| fos = null; |
| } finally { |
| if (fos != null) { |
| fos.abort(); |
| } |
| } |
| } |
| |
| public static long readFile(File file, long defaultVal) throws IOException { |
| long val = defaultVal; |
| if (file.exists()) { |
| BufferedReader br = |
| new BufferedReader(new InputStreamReader(new FileInputStream( |
| file), Charsets.UTF_8)); |
| try { |
| val = Long.parseLong(br.readLine()); |
| br.close(); |
| br = null; |
| } catch (NumberFormatException e) { |
| throw new IOException(e); |
| } finally { |
| IOUtils.cleanup(LOG, br); |
| } |
| } |
| return val; |
| } |
| } |