/**
    *
    * 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.master;
  
  import java.io.IOException;
  import java.lang.Thread.UncaughtExceptionHandler;
  import java.util.concurrent.Executors;
  
  import org.apache.hadoop.hbase.classification.InterfaceAudience;
  import org.apache.hadoop.hbase.Server;
  
  import com.google.common.util.concurrent.ThreadFactoryBuilder;
  
  /**
   * Base class used bulk assigning and unassigning regions.
   * Encapsulates a fixed size thread pool of executors to run assignment/unassignment.
   * Implement {@link #populatePool(java.util.concurrent.ExecutorService)} and
   * {@link #waitUntilDone(long)}.  The default implementation of
   * the {@link #getUncaughtExceptionHandler()} is to abort the hosting
   * Server.
   */
  @InterfaceAudience.Private
  public abstract class BulkAssigner {
    protected final Server server;
  
    /**
     * @param server An instance of Server
     */
    public BulkAssigner(final Server server) {
      this.server = server;
    }
  
    /**
     * @return What to use for a thread prefix when executor runs.
     */
    protected String getThreadNamePrefix() {
      return this.server.getServerName() + "-" + this.getClass().getName(); 
    }
  
    protected UncaughtExceptionHandler getUncaughtExceptionHandler() {
      return new UncaughtExceptionHandler() {
        @Override
        public void uncaughtException(Thread t, Throwable e) {
          // Abort if exception of any kind.
          server.abort("Uncaught exception in " + t.getName(), e);
        }
      };
    }
  
    protected int getThreadCount() {
      return this.server.getConfiguration().
        getInt("hbase.bulk.assignment.threadpool.size", 20);
    }
  
    protected long getTimeoutOnRIT() {
      return this.server.getConfiguration().
        getLong("hbase.bulk.assignment.waiton.empty.rit", 5 * 60 * 1000);
    }
  
    protected abstract void populatePool(
        final java.util.concurrent.ExecutorService pool) throws IOException;
  
    public boolean bulkAssign() throws InterruptedException, IOException {
      return bulkAssign(true);
    }
  
    /**
     * Run the bulk assign.
     * 
     * @param sync
     *          Whether to assign synchronously.
     * @throws InterruptedException
     * @return True if done.
     * @throws IOException
     */
    public boolean bulkAssign(boolean sync) throws InterruptedException,
        IOException {
      boolean result = false;
      ThreadFactoryBuilder builder = new ThreadFactoryBuilder();
      builder.setDaemon(true);
      builder.setNameFormat(getThreadNamePrefix() + "-%1$d");
      builder.setUncaughtExceptionHandler(getUncaughtExceptionHandler());
      int threadCount = getThreadCount();
     java.util.concurrent.ExecutorService pool =
       Executors.newFixedThreadPool(threadCount, builder.build());
     try {
       populatePool(pool);
       // How long to wait on empty regions-in-transition.  If we timeout, the
       // RIT monitor should do fixup.
       if (sync) result = waitUntilDone(getTimeoutOnRIT());
     } finally {
       // We're done with the pool.  It'll exit when its done all in queue.
       pool.shutdown();
     }
     return result;
   }
 
   /**
    * Wait until bulk assign is done.
    * @param timeout How long to wait.
    * @throws InterruptedException
    * @return True if the condition we were waiting on happened.
    */
   protected abstract boolean waitUntilDone(final long timeout)
   throws InterruptedException;
 }