Github user revans2 commented on a diff in the pull request:
https://github.com/apache/storm/pull/936#discussion_r49210908
--- Diff:
external/storm-hdfs/src/main/java/org/apache/storm/hdfs/spout/DirLock.java ---
@@ -0,0 +1,133 @@
+/**
+ * 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
+ * <p/>
+ * http://www.apache.org/licenses/LICENSE-2.0
+ * <p/>
+ * 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.storm.hdfs.spout;
+
+import org.apache.hadoop.fs.FSDataOutputStream;
+import org.apache.hadoop.fs.FileSystem;
+import org.apache.hadoop.fs.Path;
+import org.apache.hadoop.hdfs.DistributedFileSystem;
+import org.apache.storm.hdfs.common.HdfsUtils;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import java.io.IOException;
+
+/**
+ * Facility to synchronize access to HDFS directory. The lock itself is
represented
+ * as a file in the same directory. Relies on atomic file creation.
+ */
+public class DirLock {
+ private FileSystem fs;
+ private final Path lockFile;
+ public static final String DIR_LOCK_FILE = "DIRLOCK";
+ private static final Logger LOG = LoggerFactory.getLogger(DirLock.class);
+ private DirLock(FileSystem fs, Path lockFile) throws IOException {
+ if( fs.isDirectory(lockFile) ) {
+ throw new IllegalArgumentException(lockFile.toString() + " is not a
directory");
+ }
+ this.fs = fs;
+ this.lockFile = lockFile;
+ }
+
+ /** Get a lock on file if not already locked
+ *
+ * @param fs
+ * @param dir the dir on which to get a lock
+ * @return The lock object if it the lock was acquired. Returns null if
the dir is already locked.
+ * @throws IOException if there were errors
+ */
+ public static DirLock tryLock(FileSystem fs, Path dir) throws
IOException {
+ Path lockFile = getDirLockFile(dir);
+
+ try {
+ FSDataOutputStream ostream = HdfsUtils.tryCreateFile(fs, lockFile);
+ if (ostream!=null) {
+ LOG.debug("Thread ({}) Acquired lock on dir {}", threadInfo(),
dir);
+ ostream.close();
+ return new DirLock(fs, lockFile);
+ } else {
+ LOG.debug("Thread ({}) cannot lock dir {} as its already locked.",
threadInfo(), dir);
+ return null;
+ }
+ } catch (IOException e) {
+ LOG.error("Error when acquiring lock on dir " + dir, e);
+ throw e;
+ }
+ }
+
+ private static Path getDirLockFile(Path dir) {
+ return new Path(dir.toString() + Path.SEPARATOR_CHAR + DIR_LOCK_FILE );
+ }
+
+ private static String threadInfo () {
+ return "ThdId=" + Thread.currentThread().getId() + ", ThdName="
+ + Thread.currentThread().getName();
+ }
+
+ /** Release lock on dir by deleting the lock file */
+ public void release() throws IOException {
+ if(!fs.delete(lockFile, false)) {
+ LOG.error("Thread {} could not delete dir lock {} ", threadInfo(),
lockFile);
+ }
+ else {
+ LOG.debug("Thread {} Released dir lock {} ", threadInfo(), lockFile);
+ }
+ }
+
+ /** if the lock on the directory is stale, take ownership */
+ public static DirLock takeOwnershipIfStale(FileSystem fs, Path
dirToLock, int lockTimeoutSec) {
+ Path dirLockFile = getDirLockFile(dirToLock);
+
+ long now = System.currentTimeMillis();
+ long expiryTime = now - (lockTimeoutSec*1000);
+
+ try {
+ long modTime = fs.getFileStatus(dirLockFile).getModificationTime();
+ if(modTime <= expiryTime) {
+ return takeOwnership(fs, dirLockFile);
+ }
+ return null;
+ } catch (IOException e) {
+ return null;
+ }
+ }
+
+ private static DirLock takeOwnership(FileSystem fs, Path dirLockFile)
throws IOException {
+ if(fs instanceof DistributedFileSystem) {
+ if (!((DistributedFileSystem) fs).recoverLease(dirLockFile)) {
+ LOG.warn("Unable to recover lease on dir lock file " + dirLockFile
+ " right now. Cannot transfer ownership. Will need to try later.");
+ return null;
+ }
+ }
+
+ // delete and recreate lock file
+ if( fs.delete(dirLockFile, false) ) { // returns false if somebody
else already deleted it (to take ownership)
+ FSDataOutputStream ostream = HdfsUtils.tryCreateFile(fs,
dirLockFile);
+ if(ostream!=null) {
+ ostream.close();
+ }
+ return new DirLock(fs, dirLockFile);
+ }
+ return null;
--- End diff --
Shuldn't we just replace this part with tryLock? The code is almost
identical except for extra debugging that I think would be good.
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