| /* |
| * 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.nutch.util; |
| |
| import java.io.IOException; |
| |
| import org.apache.hadoop.conf.Configuration; |
| import org.apache.hadoop.fs.FileSystem; |
| import org.apache.hadoop.fs.Path; |
| |
| /** |
| * Utility methods for handling application-level locking. |
| * |
| * @author Andrzej Bialecki |
| */ |
| public class LockUtil { |
| |
| /** |
| * Create a lock file. |
| * |
| * @param fs |
| * filesystem |
| * @param lockFile |
| * name of the lock file |
| * @param accept |
| * if true, and the target file exists, consider it valid. If false |
| * and the target file exists, throw an IOException. |
| * @throws IOException |
| * if accept is false, and the target file already exists, or if |
| * it's a directory. |
| */ |
| public static void createLockFile(FileSystem fs, Path lockFile, boolean accept) |
| throws IOException { |
| if (fs.exists(lockFile)) { |
| if (!accept) |
| throw new IOException("lock file " + lockFile + " already exists."); |
| if (fs.getFileStatus(lockFile).isDirectory()) |
| throw new IOException("lock file " + lockFile |
| + " already exists and is a directory."); |
| // do nothing - the file already exists. |
| } else { |
| // make sure parents exist |
| fs.mkdirs(lockFile.getParent()); |
| fs.createNewFile(lockFile); |
| } |
| } |
| |
| /** |
| * Create a lock file. |
| * |
| * @param conf |
| * configuration to find the {@link org.apache.hadoop.fs.FileSystem FileSystem} lockFile |
| * belongs to |
| * @param lockFile |
| * name of the lock file |
| * @param accept |
| * if true, and the target file exists, consider it valid. If false |
| * and the target file exists, throw an IOException. |
| * @throws IOException |
| * if accept is false, and the target file already exists, or if |
| * it's a directory. |
| */ |
| public static void createLockFile(Configuration conf, Path lockFile, boolean accept) |
| throws IOException { |
| FileSystem fs = lockFile.getFileSystem(conf); |
| createLockFile(fs, lockFile, accept); |
| } |
| |
| /** |
| * Remove lock file. NOTE: applications enforce the semantics of this file - |
| * this method simply removes any file with a given name. |
| * |
| * @param fs |
| * filesystem |
| * @param lockFile |
| * lock file name |
| * @return false, if the lock file doesn't exist. True, if it existed and was |
| * successfully removed. |
| * @throws IOException |
| * if lock file exists but it is a directory. |
| */ |
| public static boolean removeLockFile(FileSystem fs, Path lockFile) |
| throws IOException { |
| if (!fs.exists(lockFile)) |
| return false; |
| if (fs.getFileStatus(lockFile).isDirectory()) |
| throw new IOException("lock file " + lockFile |
| + " exists but is a directory!"); |
| return fs.delete(lockFile, false); |
| } |
| |
| /** |
| * Remove lock file. NOTE: applications enforce the semantics of this file - |
| * this method simply removes any file with a given name. |
| * |
| * @param conf |
| * configuration to find the {@link org.apache.hadoop.fs.FileSystem FileSystem} lockFile |
| * belongs to |
| * @param lockFile |
| * lock file name |
| * @return false, if the lock file doesn't exist. True, if it existed and was |
| * successfully removed. |
| * @throws IOException |
| * if lock file exists but it is a directory. |
| */ |
| public static boolean removeLockFile(Configuration conf, Path lockFile) |
| throws IOException { |
| FileSystem fs = lockFile.getFileSystem(conf); |
| return removeLockFile(fs, lockFile); |
| } |
| |
| } |