Java tutorial
/** * 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.util; import java.io.File; import java.io.FileNotFoundException; import java.io.FileOutputStream; import java.io.IOException; import java.util.UUID; import java.util.concurrent.atomic.AtomicReference; import com.google.common.annotations.VisibleForTesting; import org.apache.commons.io.FileUtils; import org.apache.hadoop.classification.InterfaceAudience; import org.apache.hadoop.classification.InterfaceStability; import org.apache.hadoop.fs.FileUtil; import org.apache.hadoop.fs.LocalFileSystem; import org.apache.hadoop.fs.Path; import org.apache.hadoop.fs.permission.FsPermission; import org.apache.hadoop.io.IOUtils; import org.slf4j.Logger; import org.slf4j.LoggerFactory; /** * Class that provides utility functions for checking disk problem */ @InterfaceAudience.Private @InterfaceStability.Unstable public class DiskChecker { public static final Logger LOG = LoggerFactory.getLogger(DiskChecker.class); public static class DiskErrorException extends IOException { public DiskErrorException(String msg) { super(msg); } public DiskErrorException(String msg, Throwable cause) { super(msg, cause); } } public static class DiskOutOfSpaceException extends IOException { public DiskOutOfSpaceException(String msg) { super(msg); } } // Provider that abstracts some FileOutputStream operations for // testability. private static AtomicReference<FileIoProvider> fileIoProvider = new AtomicReference<>( new DefaultFileIoProvider()); /** * Create the directory if it doesn't exist and check that dir is readable, * writable and executable * * @param dir * @throws DiskErrorException */ public static void checkDir(File dir) throws DiskErrorException { checkDirInternal(dir); } /** * Create the directory if it doesn't exist and check that dir is * readable, writable and executable. Perform some disk IO to * ensure that the disk is usable for writes. * * @param dir * @throws DiskErrorException */ public static void checkDirWithDiskIo(File dir) throws DiskErrorException { checkDirInternal(dir); doDiskIo(dir); } private static void checkDirInternal(File dir) throws DiskErrorException { if (!mkdirsWithExistsCheck(dir)) { throw new DiskErrorException("Cannot create directory: " + dir.toString()); } checkAccessByFileMethods(dir); } /** * Create the local directory if necessary, check permissions and also ensure * it can be read from and written into. * * @param localFS local filesystem * @param dir directory * @param expected permission * @throws DiskErrorException * @throws IOException */ public static void checkDir(LocalFileSystem localFS, Path dir, FsPermission expected) throws DiskErrorException, IOException { checkDirInternal(localFS, dir, expected); } /** * Create the local directory if necessary, also ensure permissions * allow it to be read from and written into. Perform some diskIO * to ensure that the disk is usable for writes. * * @param localFS local filesystem * @param dir directory * @param expected permission * @throws DiskErrorException * @throws IOException */ public static void checkDirWithDiskIo(LocalFileSystem localFS, Path dir, FsPermission expected) throws DiskErrorException, IOException { checkDirInternal(localFS, dir, expected); doDiskIo(localFS.pathToFile(dir)); } private static void checkDirInternal(LocalFileSystem localFS, Path dir, FsPermission expected) throws DiskErrorException, IOException { mkdirsWithExistsAndPermissionCheck(localFS, dir, expected); checkAccessByFileMethods(localFS.pathToFile(dir)); } /** * Checks that the current running process can read, write, and execute the * given directory by using methods of the File object. * * @param dir File to check * @throws DiskErrorException if dir is not readable, not writable, or not * executable */ private static void checkAccessByFileMethods(File dir) throws DiskErrorException { if (!dir.isDirectory()) { throw new DiskErrorException("Not a directory: " + dir.toString()); } if (!FileUtil.canRead(dir)) { throw new DiskErrorException("Directory is not readable: " + dir.toString()); } if (!FileUtil.canWrite(dir)) { throw new DiskErrorException("Directory is not writable: " + dir.toString()); } if (!FileUtil.canExecute(dir)) { throw new DiskErrorException("Directory is not executable: " + dir.toString()); } } /** * The semantics of mkdirsWithExistsCheck method is different from the mkdirs * method provided in the Sun's java.io.File class in the following way: * While creating the non-existent parent directories, this method checks for * the existence of those directories if the mkdir fails at any point (since * that directory might have just been created by some other process). * If both mkdir() and the exists() check fails for any seemingly * non-existent directory, then we signal an error; Sun's mkdir would signal * an error (return false) if a directory it is attempting to create already * exists or the mkdir fails. * @param dir * @return true on success, false on failure */ private static boolean mkdirsWithExistsCheck(File dir) { if (dir.mkdir() || dir.exists()) { return true; } File canonDir; try { canonDir = dir.getCanonicalFile(); } catch (IOException e) { return false; } String parent = canonDir.getParent(); return (parent != null) && (mkdirsWithExistsCheck(new File(parent)) && (canonDir.mkdir() || canonDir.exists())); } /** * Create the directory or check permissions if it already exists. * * The semantics of mkdirsWithExistsAndPermissionCheck method is different * from the mkdirs method provided in the Sun's java.io.File class in the * following way: * While creating the non-existent parent directories, this method checks for * the existence of those directories if the mkdir fails at any point (since * that directory might have just been created by some other process). * If both mkdir() and the exists() check fails for any seemingly * non-existent directory, then we signal an error; Sun's mkdir would signal * an error (return false) if a directory it is attempting to create already * exists or the mkdir fails. * * @param localFS local filesystem * @param dir directory to be created or checked * @param expected expected permission * @throws IOException */ static void mkdirsWithExistsAndPermissionCheck(LocalFileSystem localFS, Path dir, FsPermission expected) throws IOException { File directory = localFS.pathToFile(dir); boolean created = false; if (!directory.exists()) created = mkdirsWithExistsCheck(directory); if (created || !localFS.getFileStatus(dir).getPermission().equals(expected)) localFS.setPermission(dir, expected); } // State related to running disk IO checks. private static final String DISK_IO_FILE_PREFIX = "DiskChecker.OK_TO_DELETE_."; @VisibleForTesting static final int DISK_IO_MAX_ITERATIONS = 3; /** * Performs some disk IO by writing to a new file in the given directory * and sync'ing file contents to disk. * * This increases the likelihood of catching catastrophic disk/controller * failures sooner. * * @param dir directory to be checked. * @throws DiskErrorException if we hit an error while trying to perform * disk IO against the file. */ private static void doDiskIo(File dir) throws DiskErrorException { try { IOException ioe = null; for (int i = 0; i < DISK_IO_MAX_ITERATIONS; ++i) { final File file = getFileNameForDiskIoCheck(dir, i + 1); try { diskIoCheckWithoutNativeIo(file); return; } catch (IOException e) { // Let's retry a few times before we really give up and // declare the disk as bad. ioe = e; } } throw ioe; // Just rethrow the last exception to signal failure. } catch (IOException e) { throw new DiskErrorException("Error checking directory " + dir, e); } } /** * Try to perform some disk IO by writing to the given file * without using Native IO. * * @param file * @throws IOException if there was a non-retriable error. */ private static void diskIoCheckWithoutNativeIo(File file) throws IOException { FileOutputStream fos = null; try { final FileIoProvider provider = fileIoProvider.get(); fos = provider.get(file); provider.write(fos, new byte[1]); fos.getFD().sync(); fos.close(); fos = null; if (!file.delete() && file.exists()) { throw new IOException("Failed to delete " + file); } file = null; } finally { IOUtils.cleanup(null, fos); FileUtils.deleteQuietly(file); } } /** * Generate a path name for a test file under the given directory. * * @return file object. */ @VisibleForTesting static File getFileNameForDiskIoCheck(File dir, int iterationCount) { if (iterationCount < DISK_IO_MAX_ITERATIONS) { // Use file names of the format prefix.001 by default. return new File(dir, DISK_IO_FILE_PREFIX + String.format("%03d", iterationCount)); } else { // If the first few checks then fail, try using a randomly generated // file name. return new File(dir, DISK_IO_FILE_PREFIX + UUID.randomUUID()); } } /** * An interface that abstracts operations on {@link FileOutputStream} * objects for testability. */ interface FileIoProvider { FileOutputStream get(File f) throws FileNotFoundException; void write(FileOutputStream fos, byte[] data) throws IOException; } /** * The default implementation of {@link FileIoProvider}. */ private static class DefaultFileIoProvider implements FileIoProvider { /** * See {@link FileOutputStream#FileOutputStream(File)}. */ @Override public FileOutputStream get(File f) throws FileNotFoundException { return new FileOutputStream(f); } /** * See {@link FileOutputStream#write(byte[])}. */ @Override public void write(FileOutputStream fos, byte[] data) throws IOException { fos.write(data); } } /** * Replace the {@link FileIoProvider} for tests. * This method MUST NOT be used outside of unit tests. * * @param newFosProvider * @return the old FileIoProvider. */ @VisibleForTesting static FileIoProvider replaceFileOutputStreamProvider(FileIoProvider newFosProvider) { return fileIoProvider.getAndSet(newFosProvider); } /** * Retrieve the current {@link FileIoProvider}. * This method MUST NOT be used outside of unit tests. * * @return the current FileIoProvider. */ @VisibleForTesting static FileIoProvider getFileOutputStreamProvider() { return fileIoProvider.get(); } }