| /** |
| * 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.Closeable; |
| import java.io.File; |
| import java.io.FileNotFoundException; |
| import java.io.IOException; |
| import java.io.RandomAccessFile; |
| import java.nio.ByteBuffer; |
| import java.nio.channels.FileChannel; |
| |
| import org.apache.hadoop.classification.InterfaceAudience; |
| import org.apache.hadoop.io.IOUtils; |
| |
| import org.apache.hadoop.thirdparty.com.google.common.io.Files; |
| import org.apache.hadoop.thirdparty.com.google.common.primitives.Longs; |
| |
| /** |
| * Class that represents a file on disk which stores a single <code>long</code> |
| * value, but does not make any effort to make it truly durable. This is in |
| * contrast to {@link PersistentLongFile} which fsync()s the value on every |
| * change. |
| * |
| * This should be used for values which are updated frequently (such that |
| * performance is important) and not required to be up-to-date for correctness. |
| * |
| * This class also differs in that it stores the value as binary data instead |
| * of a textual string. |
| */ |
| @InterfaceAudience.Private |
| public class BestEffortLongFile implements Closeable { |
| |
| private final File file; |
| private final long defaultVal; |
| |
| private long value; |
| |
| private FileChannel ch = null; |
| |
| private final ByteBuffer buf = ByteBuffer.allocate(Long.SIZE/8); |
| |
| public BestEffortLongFile(File file, long defaultVal) { |
| this.file = file; |
| this.defaultVal = defaultVal; |
| } |
| |
| public long get() throws IOException { |
| lazyOpen(); |
| return value; |
| } |
| |
| public void set(long newVal) throws IOException { |
| lazyOpen(); |
| buf.clear(); |
| buf.putLong(newVal); |
| buf.flip(); |
| IOUtils.writeFully(ch, buf, 0); |
| value = newVal; |
| } |
| |
| private void lazyOpen() throws IOException { |
| if (ch != null) { |
| return; |
| } |
| |
| // Load current value. |
| byte[] data = null; |
| try { |
| data = Files.toByteArray(file); |
| } catch (FileNotFoundException fnfe) { |
| // Expected - this will use default value. |
| } |
| |
| if (data != null && data.length != 0) { |
| if (data.length != Longs.BYTES) { |
| throw new IOException("File " + file + " had invalid length: " + |
| data.length); |
| } |
| value = Longs.fromByteArray(data); |
| } else { |
| value = defaultVal; |
| } |
| |
| // Now open file for future writes. |
| RandomAccessFile raf = new RandomAccessFile(file, "rw"); |
| try { |
| ch = raf.getChannel(); |
| } finally { |
| if (ch == null) { |
| IOUtils.closeStream(raf); |
| } |
| } |
| } |
| |
| @Override |
| public void close() throws IOException { |
| if (ch != null) { |
| ch.close(); |
| ch = null; |
| } |
| } |
| } |