Github user roshannaik commented on a diff in the pull request:
https://github.com/apache/storm/pull/936#discussion_r49127649
--- 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 --
I believe that is for other file systems (such as AWS) that are supported
via that class. I double checked on on HDFS semantics by talking to some HDFS
committers. Have also added UTs to check for the requisite Hdfs atomicity/other
semantics related to create, append and delete as an added safeguard. We will
see failures in these tests if the guarantees are being violated. These are the
relevant UT tests: TestHdfsSemantics.* TestFileLock.testConcurrentLocking,
TestDirLock.testConcurrentLocking
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