Github user arunmahadevan commented on a diff in the pull request:
https://github.com/apache/storm/pull/936#discussion_r49158800
--- 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);
--- End diff --
The RawLocalFileSystem implementation does not seem to take care of
atomicity -
[link](https://github.com/apache/hadoop/blob/trunk/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/fs/RawLocalFileSystem.java#L299).
In the distributed mode name node could guarantee atomicity by locking, but I
havent checked the details. Did you run the tests in local or distributed mode
? Anyways it would be hard to get the order and timing right for the tests to
fail.
It might be good to add some comments/docs to call out that the locking
semantics depends on the underlying implementation guarantees.
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