| /* |
| * 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.lucene.store; |
| |
| |
| import java.io.IOException; |
| import java.nio.file.AccessDeniedException; |
| import java.nio.file.FileAlreadyExistsException; |
| import java.nio.file.Files; |
| import java.nio.file.Path; |
| import java.nio.file.attribute.BasicFileAttributes; |
| import java.nio.file.attribute.FileTime; |
| |
| /** |
| * <p>Implements {@link LockFactory} using {@link |
| * Files#createFile}.</p> |
| * |
| * <p>The main downside with using this API for locking is |
| * that the Lucene write lock may not be released when |
| * the JVM exits abnormally.</p> |
| * |
| * <p>When this happens, an {@link LockObtainFailedException} |
| * is hit when trying to create a writer, in which case you may |
| * need to explicitly clear the lock file first by |
| * manually removing the file. But, first be certain that |
| * no writer is in fact writing to the index otherwise you |
| * can easily corrupt your index.</p> |
| * |
| * <p>Special care needs to be taken if you change the locking |
| * implementation: First be certain that no writer is in fact |
| * writing to the index otherwise you can easily corrupt |
| * your index. Be sure to do the LockFactory change all Lucene |
| * instances and clean up all leftover lock files before starting |
| * the new configuration for the first time. Different implementations |
| * can not work together!</p> |
| * |
| * <p>If you suspect that this or any other LockFactory is |
| * not working properly in your environment, you can easily |
| * test it by using {@link VerifyingLockFactory}, {@link |
| * LockVerifyServer} and {@link LockStressTest}.</p> |
| * |
| * <p>This is a singleton, you have to use {@link #INSTANCE}. |
| * |
| * @see LockFactory |
| */ |
| |
| public final class SimpleFSLockFactory extends FSLockFactory { |
| |
| /** |
| * Singleton instance |
| */ |
| public static final SimpleFSLockFactory INSTANCE = new SimpleFSLockFactory(); |
| |
| private SimpleFSLockFactory() {} |
| |
| @Override |
| protected Lock obtainFSLock(FSDirectory dir, String lockName) throws IOException { |
| Path lockDir = dir.getDirectory(); |
| |
| // Ensure that lockDir exists and is a directory. |
| // note: this will fail if lockDir is a symlink |
| Files.createDirectories(lockDir); |
| |
| Path lockFile = lockDir.resolve(lockName); |
| |
| // create the file: this will fail if it already exists |
| try { |
| Files.createFile(lockFile); |
| } catch (FileAlreadyExistsException | AccessDeniedException e) { |
| // convert optional specific exception to our optional specific exception |
| throw new LockObtainFailedException("Lock held elsewhere: " + lockFile, e); |
| } |
| |
| // used as a best-effort check, to see if the underlying file has changed |
| final FileTime creationTime = Files.readAttributes(lockFile, BasicFileAttributes.class).creationTime(); |
| |
| return new SimpleFSLock(lockFile, creationTime); |
| } |
| |
| static final class SimpleFSLock extends Lock { |
| private final Path path; |
| private final FileTime creationTime; |
| private volatile boolean closed; |
| |
| SimpleFSLock(Path path, FileTime creationTime) throws IOException { |
| this.path = path; |
| this.creationTime = creationTime; |
| } |
| |
| @Override |
| public void ensureValid() throws IOException { |
| if (closed) { |
| throw new AlreadyClosedException("Lock instance already released: " + this); |
| } |
| // try to validate the backing file name, that it still exists, |
| // and has the same creation time as when we obtained the lock. |
| // if it differs, someone deleted our lock file (and we are ineffective) |
| FileTime ctime = Files.readAttributes(path, BasicFileAttributes.class).creationTime(); |
| if (!creationTime.equals(ctime)) { |
| throw new AlreadyClosedException("Underlying file changed by an external force at " + ctime + ", (lock=" + this + ")"); |
| } |
| } |
| |
| @Override |
| public synchronized void close() throws IOException { |
| if (closed) { |
| return; |
| } |
| try { |
| // NOTE: unlike NativeFSLockFactory, we can potentially delete someone else's |
| // lock if things have gone wrong. we do best-effort check (ensureValid) to |
| // avoid doing this. |
| try { |
| ensureValid(); |
| } catch (Throwable exc) { |
| // notify the user they may need to intervene. |
| throw new LockReleaseFailedException("Lock file cannot be safely removed. Manual intervention is recommended.", exc); |
| } |
| // we did a best effort check, now try to remove the file. if something goes wrong, |
| // we need to make it clear to the user that the directory may still remain locked. |
| try { |
| Files.delete(path); |
| } catch (Throwable exc) { |
| throw new LockReleaseFailedException("Unable to remove lock file. Manual intervention is recommended", exc); |
| } |
| } finally { |
| closed = true; |
| } |
| } |
| |
| @Override |
| public String toString() { |
| return "SimpleFSLock(path=" + path + ",creationTime=" + creationTime + ")"; |
| } |
| } |
| } |