content: /**
   * 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 com.alibaba.jstorm.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 com.alibaba.jstorm.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;
    }
  
    public Path getLockFile() {
      return lockFile;
    }
  }
  