/**
    *
    * 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.
   */
  package org.apache.hadoop.hbase.regionserver;
  
  import java.io.FileNotFoundException;
  import java.io.IOException;
  import java.io.InterruptedIOException;
  import java.net.ConnectException;
  import java.net.SocketTimeoutException;
  
  import org.apache.commons.logging.Log;
  import org.apache.commons.logging.LogFactory;
  import org.apache.hadoop.hbase.classification.InterfaceAudience;
  import org.apache.hadoop.conf.Configuration;
  import org.apache.hadoop.fs.FileSystem;
  import org.apache.hadoop.fs.Path;
  import org.apache.hadoop.hbase.NotServingRegionException;
  import org.apache.hadoop.hbase.Server;
  import org.apache.hadoop.hbase.client.RetriesExhaustedException;
  import org.apache.hadoop.hbase.coordination.BaseCoordinatedStateManager;
  import org.apache.hadoop.hbase.coordination.SplitLogWorkerCoordination;
  import org.apache.hadoop.hbase.protobuf.generated.ZooKeeperProtos.SplitLogTask.RecoveryMode;
  import org.apache.hadoop.hbase.wal.WALFactory;
  import org.apache.hadoop.hbase.wal.WALSplitter;
  import org.apache.hadoop.hbase.util.CancelableProgressable;
  import org.apache.hadoop.hbase.util.ExceptionUtil;
  import org.apache.hadoop.hbase.util.FSUtils;
  
  /**
   * This worker is spawned in every regionserver, including master. The Worker waits for log
   * splitting tasks to be put up by the {@link org.apache.hadoop.hbase.master.SplitLogManager} 
   * running in the master and races with other workers in other serves to acquire those tasks. 
   * The coordination is done via coordination engine.
   * <p>
   * If a worker has successfully moved the task from state UNASSIGNED to OWNED then it owns the task.
   * It keeps heart beating the manager by periodically moving the task from UNASSIGNED to OWNED
   * state. On success it moves the task to TASK_DONE. On unrecoverable error it moves task state to
   * ERR. If it cannot continue but wants the master to retry the task then it moves the task state to
   * RESIGNED.
   * <p>
   * The manager can take a task away from a worker by moving the task from OWNED to UNASSIGNED. In
   * the absence of a global lock there is a unavoidable race here - a worker might have just finished
   * its task when it is stripped of its ownership. Here we rely on the idempotency of the log
   * splitting task for correctness
   */
  @InterfaceAudience.Private
  public class SplitLogWorker implements Runnable {
  
    private static final Log LOG = LogFactory.getLog(SplitLogWorker.class);
  
    Thread worker;
    // thread pool which executes recovery work
    private SplitLogWorkerCoordination coordination;
    private Configuration conf;
    private RegionServerServices server;
  
    public SplitLogWorker(Server hserver, Configuration conf, RegionServerServices server,
        TaskExecutor splitTaskExecutor) {
      this.server = server;
      this.conf = conf;
      this.coordination =
          ((BaseCoordinatedStateManager) hserver.getCoordinatedStateManager())
              .getSplitLogWorkerCoordination();
      this.server = server;
      coordination.init(server, conf, splitTaskExecutor, this);
    }
  
    public SplitLogWorker(final Server hserver, final Configuration conf,
        final RegionServerServices rsServices, final LastSequenceId sequenceIdChecker,
        final WALFactory factory) {
      this(hserver, conf, rsServices, new TaskExecutor() {
        @Override
        public Status exec(String filename, RecoveryMode mode, CancelableProgressable p) {
          Path walDir;
          FileSystem fs;
          try {
            walDir = FSUtils.getWALRootDir(conf);
            fs = walDir.getFileSystem(conf);
          } catch (IOException e) {
            LOG.warn("could not find root dir or fs", e);
            return Status.RESIGNED;
          }
          // TODO have to correctly figure out when log splitting has been
         // interrupted or has encountered a transient error and when it has
         // encountered a bad non-retry-able persistent error.
         try {
           if (!WALSplitter.splitLogFile(walDir, fs.getFileStatus(new Path(walDir, filename)),
             fs, conf, p, sequenceIdChecker, rsServices.getCoordinatedStateManager(), mode, factory)) {
             return Status.PREEMPTED;
           }
         } catch (InterruptedIOException iioe) {
           LOG.warn("log splitting of " + filename + " interrupted, resigning", iioe);
           return Status.RESIGNED;
         } catch (IOException e) {
           if (e instanceof FileNotFoundException) {
             // A wal file may not exist anymore. Nothing can be recovered so move on
             LOG.warn("WAL " + filename + " does not exist anymore", e);
             return Status.DONE;
           }
           Throwable cause = e.getCause();
           if (e instanceof RetriesExhaustedException && (cause instanceof NotServingRegionException
                   || cause instanceof ConnectException
                   || cause instanceof SocketTimeoutException)) {
             LOG.warn("log replaying of " + filename + " can't connect to the target regionserver, "
                 + "resigning", e);
             return Status.RESIGNED;
           } else if (cause instanceof InterruptedException) {
             LOG.warn("log splitting of " + filename + " interrupted, resigning", e);
             return Status.RESIGNED;
           }
           LOG.warn("log splitting of " + filename + " failed, returning error", e);
           return Status.ERR;
         }
         return Status.DONE;
       }
     });
   }
 
   @Override
   public void run() {
     try {
       LOG.info("SplitLogWorker " + server.getServerName() + " starting");
       coordination.registerListener();
       // wait for Coordination Engine is ready
       boolean res = false;
       while (!res && !coordination.isStop()) {
         res = coordination.isReady();
       }
       if (!coordination.isStop()) {
         coordination.taskLoop();
       }
     } catch (Throwable t) {
       if (ExceptionUtil.isInterrupt(t)) {
         LOG.info("SplitLogWorker interrupted. Exiting. " + (coordination.isStop() ? "" :
             " (ERROR: exitWorker is not set, exiting anyway)"));
       } else {
         // only a logical error can cause here. Printing it out
         // to make debugging easier
         LOG.error("unexpected error ", t);
       }
     } finally {
       coordination.removeListener();
       LOG.info("SplitLogWorker " + server.getServerName() + " exiting");
     }
   }
 
   /**
    * If the worker is doing a task i.e. splitting a log file then stop the task.
    * It doesn't exit the worker thread.
    */
   public void stopTask() {
     LOG.info("Sending interrupt to stop the worker thread");
     worker.interrupt(); // TODO interrupt often gets swallowed, do what else?
   }
 
   /**
    * start the SplitLogWorker thread
    */
   public void start() {
     worker = new Thread(null, this, "SplitLogWorker-" + server.getServerName().toShortString());
     worker.start();
   }
 
   /**
    * stop the SplitLogWorker thread
    */
   public void stop() {
     coordination.stopProcessingTasks();
     stopTask();
   }
 
   /**
    * Objects implementing this interface actually do the task that has been
    * acquired by a {@link SplitLogWorker}. Since there isn't a water-tight
    * guarantee that two workers will not be executing the same task therefore it
    * is better to have workers prepare the task and then have the
    * {@link org.apache.hadoop.hbase.master.SplitLogManager} commit the work in 
    * SplitLogManager.TaskFinisher
    */
   public interface TaskExecutor {
     enum Status {
       DONE(),
       ERR(),
       RESIGNED(),
       PREEMPTED()
     }
     Status exec(String name, RecoveryMode mode, CancelableProgressable p);
   }
 
   /**
    * Returns the number of tasks processed by coordination.
    * This method is used by tests only
    */
   public int getTaskReadySeq() {
     return coordination.getTaskReadySeq();
   }
 }