FileSystem: Use XNativeFSLockFactory instead of the buggy Lucene 4.8.…

…1 version

There is a pretty nasty bug in the lock factory we use that can cause
nodes to use the same data dir wiping each others data. Luckily this is
unlikely to happen if the nodes are running in different JVM which they
do unless they are embedded.

See LUCENE-5738

Closes elastic#6424

core-signatures.txt

@@ -58,3 +58,6 @@ com.google.common.primitives.Longs#compare(long,long)
 
 @defaultMessage we have an optimized XStringField to reduce analysis creation overhead
 org.apache.lucene.document.Field#<init>(java.lang.String,java.lang.String,org.apache.lucene.document.FieldType)
+
+@defaultMessage Use XNativeFSLockFactory instead of the buggy NativeFSLockFactory see LUCENE-5738 - remove once Lucene 4.9 is released
+org.apache.lucene.store.NativeFSLockFactory

src/main/java/org/apache/lucene/store/XNativeFSLockFactory.java

@@ -0,0 +1,246 @@
+package org.apache.lucene.store;
+
+/*
+ * 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.
+ */
+
+import java.nio.channels.FileChannel;
+import java.nio.channels.FileLock;
+import java.nio.channels.OverlappingFileLockException;
+import java.nio.file.StandardOpenOption;
+import java.io.File;
+import java.io.IOException;
+import java.util.Collections;
+import java.util.HashSet;
+import java.util.Set;
+
+import org.apache.lucene.util.IOUtils;
+import org.elasticsearch.Version;
+
+/**
+ * <p>Implements {@link LockFactory} using native OS file
+ * locks.  Note that because this LockFactory relies on
+ * java.nio.* APIs for locking, any problems with those APIs
+ * will cause locking to fail.  Specifically, on certain NFS
+ * environments the java.nio.* locks will fail (the lock can
+ * incorrectly be double acquired) whereas {@link
+ * SimpleFSLockFactory} worked perfectly in those same
+ * environments.  For NFS based access to an index, it's
+ * recommended that you try {@link SimpleFSLockFactory}
+ * first and work around the one limitation that a lock file
+ * could be left when the JVM exits abnormally.</p>
+ *
+ * <p>The primary benefit of {@link XNativeFSLockFactory} is
+ * that locks (not the lock file itsself) will be properly
+ * removed (by the OS) if the JVM has an abnormal exit.</p>
+ * 
+ * <p>Note that, unlike {@link SimpleFSLockFactory}, the existence of
+ * leftover lock files in the filesystem is fine because the OS
+ * will free the locks held against these files even though the
+ * files still remain. Lucene will never actively remove the lock
+ * files, so although you see them, the index may not be locked.</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 on 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>
+ *
+ * @see LockFactory
+ */
+
+public class XNativeFSLockFactory extends FSLockFactory {
+
+   static {
+       assert Version.CURRENT.luceneVersion == org.apache.lucene.util.Version.LUCENE_48 : "Remove this class in Lucene 4.9";
+   }
+
+  /**
+   * Create a XNativeFSLockFactory instance, with null (unset)
+   * lock directory. When you pass this factory to a {@link FSDirectory}
+   * subclass, the lock directory is automatically set to the
+   * directory itself. Be sure to create one instance for each directory
+   * your create!
+   */
+  public XNativeFSLockFactory() {
+    this((File) null);
+  }
+
+  /**
+   * Create a XNativeFSLockFactory instance, storing lock
+   * files into the specified lockDirName:
+   *
+   * @param lockDirName where lock files are created.
+   */
+  public XNativeFSLockFactory(String lockDirName) {
+    this(new File(lockDirName));
+  }
+
+  /**
+   * Create a XNativeFSLockFactory instance, storing lock
+   * files into the specified lockDir:
+   * 
+   * @param lockDir where lock files are created.
+   */
+  public XNativeFSLockFactory(File lockDir) {
+    setLockDir(lockDir);
+  }
+
+  @Override
+  public synchronized Lock makeLock(String lockName) {
+    if (lockPrefix != null)
+      lockName = lockPrefix + "-" + lockName;
+    return new NativeFSLock(lockDir, lockName);
+  }
+
+  @Override
+  public void clearLock(String lockName) throws IOException {
+    makeLock(lockName).close();
+  }
+}
+
+class NativeFSLock extends Lock {
+
+  private FileChannel channel;
+  private FileLock lock;
+  private File path;
+  private File lockDir;
+  private static final Set<String> LOCK_HELD = Collections.synchronizedSet(new HashSet<String>());
+
+
+  public NativeFSLock(File lockDir, String lockFileName) {
+    this.lockDir = lockDir;
+    path = new File(lockDir, lockFileName);
+  }
+
+
+  @Override
+  public synchronized boolean obtain() throws IOException {
+
+    if (lock != null) {
+      // Our instance is already locked:
+      return false;
+    }
+
+    // Ensure that lockDir exists and is a directory.
+    if (!lockDir.exists()) {
+      if (!lockDir.mkdirs())
+        throw new IOException("Cannot create directory: " +
+            lockDir.getAbsolutePath());
+    } else if (!lockDir.isDirectory()) {
+      // TODO: NoSuchDirectoryException instead?
+      throw new IOException("Found regular file where directory expected: " + 
+          lockDir.getAbsolutePath());
+    }
+    final String canonicalPath = path.getCanonicalPath();
+    // Make sure nobody else in-process has this lock held
+    // already, and, mark it held if not:
+    // This is a pretty crazy workaround for some documented
+    // but yet awkward JVM behavior:
+    //
+    //   On some systems, closing a channel releases all locks held by the Java virtual machine on the underlying file
+    //   regardless of whether the locks were acquired via that channel or via another channel open on the same file.
+    //   It is strongly recommended that, within a program, a unique channel be used to acquire all locks on any given
+    //   file.
+    //
+    // This essentially means if we close "A" channel for a given file all locks might be released... the odd part
+    // is that we can't re-obtain the lock in the same JVM but from a different process if that happens. Nevertheless
+    // this is super trappy. See LUCENE-5738
+    boolean obtained = false;
+    if (LOCK_HELD.add(canonicalPath)) {
+      try {
+        channel = FileChannel.open(path.toPath(), StandardOpenOption.CREATE, StandardOpenOption.WRITE);
+        try {
+          lock = channel.tryLock();
+          obtained = lock != null;
+        } catch (IOException | OverlappingFileLockException e) {
+          // At least on OS X, we will sometimes get an
+          // intermittent "Permission Denied" IOException,
+          // which seems to simply mean "you failed to get
+          // the lock".  But other IOExceptions could be
+          // "permanent" (eg, locking is not supported via
+          // the filesystem).  So, we record the failure
+          // reason here; the timeout obtain (usually the
+          // one calling us) will use this as "root cause"
+          // if it fails to get the lock.
+          failureReason = e;
+        }
+      } finally {
+        if (obtained == false) { // not successful - clear up and move out
+          clearLockHeld(path);
+          final FileChannel toClose = channel;
+          channel = null;
+          IOUtils.closeWhileHandlingException(toClose);
+        }
+      }
+    }
+    return obtained;
+  }
+
+  @Override
+  public synchronized void close() throws IOException {
+    try {
+      if (lock != null) {
+        try {
+          lock.release();
+          lock = null;
+        } finally {
+          clearLockHeld(path);
+        }
+      }
+    } finally {
+      IOUtils.close(channel);
+      channel = null;
+    }
+  }
+
+  private static final void clearLockHeld(File path) throws IOException {
+    boolean remove = LOCK_HELD.remove(path.getCanonicalPath());
+    assert remove : "Lock was cleared but never marked as held";
+  }
+
+  @Override
+  public synchronized boolean isLocked() {
+    // The test for is isLocked is not directly possible with native file locks:
+
+    // First a shortcut, if a lock reference in this instance is available
+    if (lock != null) return true;
+
+    // Look if lock file is present; if not, there can definitely be no lock!
+    if (!path.exists()) return false;
+
+    // Try to obtain and release (if was locked) the lock
+    try {
+      boolean obtained = obtain();
+      if (obtained) close();
+      return !obtained;
+    } catch (IOException ioe) {
+      return false;
+    }    
+  }
+
+  @Override
+  public String toString() {
+    return "NativeFSLock@" + path;
+  }
+}

src/main/java/org/elasticsearch/env/NodeEnvironment.java

@@ -22,7 +22,7 @@
 import com.google.common.collect.Sets;
 import com.google.common.primitives.Ints;
 import org.apache.lucene.store.Lock;
-import org.apache.lucene.store.NativeFSLockFactory;
+import org.apache.lucene.store.XNativeFSLockFactory;
 import org.apache.lucene.util.IOUtils;
 import org.elasticsearch.ElasticsearchIllegalStateException;
 import org.elasticsearch.cluster.node.DiscoveryNode;
@@ -78,7 +78,7 @@ public NodeEnvironment(Settings settings, Environment environment) {
                 }
                 logger.trace("obtaining node lock on {} ...", dir.getAbsolutePath());
                 try {
-                    NativeFSLockFactory lockFactory = new NativeFSLockFactory(dir);
+                    XNativeFSLockFactory lockFactory = new XNativeFSLockFactory(dir);
                     Lock tmpLock = lockFactory.makeLock("node.lock");
                     boolean obtained = tmpLock.obtain();
                     if (obtained) {

src/main/java/org/elasticsearch/index/store/fs/FsDirectoryService.java

@@ -64,7 +64,7 @@ protected final LockFactory buildLockFactory() throws IOException {
         LockFactory lockFactory = NoLockFactory.getNoLockFactory();
         if (fsLock.equals("native")) {
             // TODO LUCENE MONITOR: this is not needed in next Lucene version
-            lockFactory = new NativeFSLockFactory();
+            lockFactory = new XNativeFSLockFactory();
         } else if (fsLock.equals("simple")) {
             lockFactory = new SimpleFSLockFactory();
         } else if (fsLock.equals("none")) {