/**
    *
    * 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.IOException;
  import java.lang.reflect.Field;
  import java.util.HashMap;
  import java.util.Map;
  
  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.hbase.HBaseConfiguration;
  import org.apache.hadoop.hbase.Stoppable;
  import org.apache.hadoop.hbase.util.ShutdownHookManager;
  import org.apache.hadoop.hbase.util.Threads;
  
  /**
   * Manage regionserver shutdown hooks.
   * @see #install(Configuration, FileSystem, Stoppable, Thread)
   */
  @InterfaceAudience.Private
  public class ShutdownHook {
    private static final Log LOG = LogFactory.getLog(ShutdownHook.class);
    private static final String CLIENT_FINALIZER_DATA_METHOD = "clientFinalizer";
  
    /**
     * Key for boolean configuration whose default is true.
     */
    public static final String RUN_SHUTDOWN_HOOK = "hbase.shutdown.hook";
  
    /**
     * Key for a long configuration on how much time to wait on the fs shutdown
     * hook. Default is 30 seconds.
     */
    public static final String FS_SHUTDOWN_HOOK_WAIT = "hbase.fs.shutdown.hook.wait";
  
    /**
     * A place for keeping track of all the filesystem shutdown hooks that need
     * to be executed after the last regionserver referring to a given filesystem
     * stops. We keep track of the # of regionserver references in values of the map.
     */
    private final static Map<Runnable, Integer> fsShutdownHooks = new HashMap<Runnable, Integer>();
  
    /**
     * Install a shutdown hook that calls stop on the passed Stoppable
     * and then thread joins against the passed <code>threadToJoin</code>.
     * When this thread completes, it then runs the hdfs thread (This install
     * removes the hdfs shutdown hook keeping a handle on it to run it after
     * <code>threadToJoin</code> has stopped).
     *
     * <p>To suppress all shutdown hook  handling -- both the running of the
     * regionserver hook and of the hdfs hook code -- set
     * {@link ShutdownHook#RUN_SHUTDOWN_HOOK} in {@link Configuration} to
     * <code>false</code>.
     * This configuration value is checked when the hook code runs.
     * @param conf
     * @param fs Instance of Filesystem used by the RegionServer
     * @param stop Installed shutdown hook will call stop against this passed
     * <code>Stoppable</code> instance.
     * @param threadToJoin After calling stop on <code>stop</code> will then
     * join this thread.
     */
    public static void install(final Configuration conf, final FileSystem fs,
        final Stoppable stop, final Thread threadToJoin) {
      Runnable fsShutdownHook = suppressHdfsShutdownHook(fs);
      Thread t = new ShutdownHookThread(conf, stop, threadToJoin, fsShutdownHook);
      ShutdownHookManager.affixShutdownHook(t, 0);
      LOG.debug("Installed shutdown hook thread: " + t.getName());
    }
  
    /*
     * Thread run by shutdown hook.
     */
    private static class ShutdownHookThread extends Thread {
      private final Stoppable stop;
      private final Thread threadToJoin;
      private final Runnable fsShutdownHook;
      private final Configuration conf;
  
      ShutdownHookThread(final Configuration conf, final Stoppable stop,
         final Thread threadToJoin, final Runnable fsShutdownHook) {
       super("Shutdownhook:" + threadToJoin.getName());
       this.stop = stop;
       this.threadToJoin = threadToJoin;
       this.conf = conf;
       this.fsShutdownHook = fsShutdownHook;
     }
 
     @Override
     public void run() {
       boolean b = this.conf.getBoolean(RUN_SHUTDOWN_HOOK, true);
       LOG.info("Shutdown hook starting; " + RUN_SHUTDOWN_HOOK + "=" + b +
         "; fsShutdownHook=" + this.fsShutdownHook);
       if (b) {
         this.stop.stop("Shutdown hook");
         Threads.shutdown(this.threadToJoin);
         if (this.fsShutdownHook != null) {
           synchronized (fsShutdownHooks) {
             int refs = fsShutdownHooks.get(fsShutdownHook);
             if (refs == 1) {
               LOG.info("Starting fs shutdown hook thread.");
               Thread fsShutdownHookThread = (fsShutdownHook instanceof Thread) ?
                 (Thread)fsShutdownHook : new Thread(fsShutdownHook);
               fsShutdownHookThread.start();
               Threads.shutdown(fsShutdownHookThread,
               this.conf.getLong(FS_SHUTDOWN_HOOK_WAIT, 30000));
             }
             if (refs > 0) {
               fsShutdownHooks.put(fsShutdownHook, refs - 1);
             }
           }
         }
       }
       LOG.info("Shutdown hook finished.");
     }
   }
 
   /*
    * So, HDFS keeps a static map of all FS instances. In order to make sure
    * things are cleaned up on our way out, it also creates a shutdown hook
    * so that all filesystems can be closed when the process is terminated; it
    * calls FileSystem.closeAll. This inconveniently runs concurrently with our
    * own shutdown handler, and therefore causes all the filesystems to be closed
    * before the server can do all its necessary cleanup.
    *
    * <p>The dirty reflection in this method sneaks into the FileSystem class
    * and grabs the shutdown hook, removes it from the list of active shutdown
    * hooks, and returns the hook for the caller to run at its convenience.
    *
    * <p>This seems quite fragile and susceptible to breaking if Hadoop changes
    * anything about the way this cleanup is managed. Keep an eye on things.
    * @return The fs shutdown hook
    * @throws RuntimeException if we fail to find or grap the shutdown hook.
    */
   private static Runnable suppressHdfsShutdownHook(final FileSystem fs) {
     try {
       // This introspection has been updated to work for hadoop 0.20, 0.21 and for
       // cloudera 0.20.  0.21 and cloudera 0.20 both have hadoop-4829.  With the
       // latter in place, things are a little messy in that there are now two
       // instances of the data member clientFinalizer; an uninstalled one in
       // FileSystem and one in the innner class named Cache that actually gets
       // registered as a shutdown hook.  If the latter is present, then we are
       // on 0.21 or cloudera patched 0.20.
       Runnable hdfsClientFinalizer = null;
       // Look into the FileSystem#Cache class for clientFinalizer
       Class<?> [] classes = FileSystem.class.getDeclaredClasses();
       Class<?> cache = null;
       for (Class<?> c: classes) {
         if (c.getSimpleName().equals("Cache")) {
           cache = c;
           break;
         }
       }
 
       if (cache == null) {
         throw new RuntimeException(
             "This should not happen. Could not find the cache class in FileSystem.");
       }
 
       Field field = null;
       try {
         field = cache.getDeclaredField(CLIENT_FINALIZER_DATA_METHOD);
       } catch (NoSuchFieldException e) {
         // We can get here if the Cache class does not have a clientFinalizer
         // instance: i.e. we're running on straight 0.20 w/o hadoop-4829.
       }
       if (field != null) {
         field.setAccessible(true);
         Field cacheField = FileSystem.class.getDeclaredField("CACHE");
         cacheField.setAccessible(true);
         Object cacheInstance = cacheField.get(fs);
         hdfsClientFinalizer = (Runnable)field.get(cacheInstance);
       } else {
         // Then we didnt' find clientFinalizer in Cache.  Presume clean 0.20 hadoop.
         field = FileSystem.class.getDeclaredField(CLIENT_FINALIZER_DATA_METHOD);
         field.setAccessible(true);
         hdfsClientFinalizer = (Runnable)field.get(null);
       }
       if (hdfsClientFinalizer == null) {
         throw new RuntimeException("Client finalizer is null, can't suppress!");
       }
       synchronized (fsShutdownHooks) {
         if (!fsShutdownHooks.containsKey(hdfsClientFinalizer) &&
             !ShutdownHookManager.deleteShutdownHook(hdfsClientFinalizer)) {
           throw new RuntimeException("Failed suppression of fs shutdown hook: " +
             hdfsClientFinalizer);
         }
         Integer refs = fsShutdownHooks.get(hdfsClientFinalizer);
         fsShutdownHooks.put(hdfsClientFinalizer, refs == null ? 1 : refs + 1);
       }
       return hdfsClientFinalizer;
     } catch (NoSuchFieldException nsfe) {
       LOG.fatal("Couldn't find field 'clientFinalizer' in FileSystem!", nsfe);
       throw new RuntimeException("Failed to suppress HDFS shutdown hook");
     } catch (IllegalAccessException iae) {
       LOG.fatal("Couldn't access field 'clientFinalizer' in FileSystem!", iae);
       throw new RuntimeException("Failed to suppress HDFS shutdown hook");
     }
   }
 
   // Thread that does nothing. Used in below main testing.
   static class DoNothingThread extends Thread {
     DoNothingThread() {
       super("donothing");
     }
     @Override
     public void run() {
       super.run();
     }
   }
 
   // Stoppable with nothing to stop.  Used below in main testing.
   static class DoNothingStoppable implements Stoppable {
     @Override
     public boolean isStopped() {
       // TODO Auto-generated method stub
       return false;
     }
 
     @Override
     public void stop(String why) {
       // TODO Auto-generated method stub
     }
   }
 
   /**
    * Main to test basic functionality.  Run with clean hadoop 0.20 and hadoop
    * 0.21 and cloudera patched hadoop to make sure our shutdown hook handling
    * works for all compbinations.
    * Pass '-Dhbase.shutdown.hook=false' to test turning off the running of
    * shutdown hooks.
    * @param args
    * @throws IOException
    */
   public static void main(final String [] args) throws IOException {
     Configuration conf = HBaseConfiguration.create();
     String prop = System.getProperty(RUN_SHUTDOWN_HOOK);
     if (prop != null) {
       conf.setBoolean(RUN_SHUTDOWN_HOOK, Boolean.parseBoolean(prop));
     }
     // Instantiate a FileSystem. This will register the fs shutdown hook.
     FileSystem fs = FileSystem.get(conf);
     Thread donothing = new DoNothingThread();
     donothing.start();
     ShutdownHook.install(conf, fs, new DoNothingStoppable(), donothing);
   }
 }