/**
    *
    * 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.util;
  
  import java.io.IOException;
  import java.io.InterruptedIOException;
  import java.util.List;
  import java.util.concurrent.ExecutorService;
  import java.util.concurrent.LinkedBlockingQueue;
  import java.util.concurrent.ThreadLocalRandom;
  import java.util.concurrent.ThreadPoolExecutor;
  import java.util.concurrent.TimeUnit;
  
  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.hbase.HConstants;
  import org.apache.hadoop.hbase.TableName;
  import org.apache.hadoop.hbase.client.Connection;
  import org.apache.hadoop.hbase.client.HConnection;
  import org.apache.hadoop.hbase.client.HConnectionManager;
  import org.apache.hadoop.hbase.client.Row;
  import org.apache.hadoop.hbase.client.coprocessor.Batch;
  
  /**
   * Provides ability to create multiple HConnection instances and allows to process a batch of
   * actions using HConnection.processBatchCallback()
   */
  @InterfaceAudience.Private
  public class MultiHConnection {
    private static final Log LOG = LogFactory.getLog(MultiHConnection.class);
    private HConnection[] hConnections;
    private final Object hConnectionsLock =  new Object();
    private int noOfConnections;
    private ExecutorService batchPool;
  
    /**
     * Create multiple HConnection instances and initialize a thread pool executor
     * @param conf configuration
     * @param noOfConnections total no of HConnections to create
     * @throws IOException
     */
    public MultiHConnection(Configuration conf, int noOfConnections)
        throws IOException {
      this.noOfConnections = noOfConnections;
      synchronized (this.hConnectionsLock) {
        hConnections = new HConnection[noOfConnections];
        for (int i = 0; i < noOfConnections; i++) {
          HConnection conn = HConnectionManager.createConnection(conf);
          hConnections[i] = conn;
        }
      }
      createBatchPool(conf);
    }
  
    /**
     * Close the open connections and shutdown the batchpool
     */
    public void close() {
      synchronized (hConnectionsLock) {
        if (hConnections != null) {
          for (Connection conn : hConnections) {
            if (conn != null) {
              try {
                conn.close();
              } catch (IOException e) {
                LOG.info("Got exception in closing connection", e);
              } finally {
                conn = null;
              }
            }
          }
          hConnections = null;
        }
      }
      if (this.batchPool != null && !this.batchPool.isShutdown()) {
        this.batchPool.shutdown();
        try {
          if (!this.batchPool.awaitTermination(10, TimeUnit.SECONDS)) {
            this.batchPool.shutdownNow();
          }
       } catch (InterruptedException e) {
         this.batchPool.shutdownNow();
       }
     }
 
   }
 
   /**
    * Randomly pick a connection and process the batch of actions for a given table
    * @param actions the actions
    * @param tableName table name
    * @param results the results array
    * @param callback 
    * @throws IOException
    */
   @SuppressWarnings("deprecation")
   public <R> void processBatchCallback(List<? extends Row> actions, TableName tableName,
       Object[] results, Batch.Callback<R> callback) throws IOException {
     // Currently used by RegionStateStore
     // A deprecated method is used as multiple threads accessing RegionStateStore do a single put
     // and htable is not thread safe. Alternative would be to create an Htable instance for each 
     // put but that is not very efficient.
     // See HBASE-11610 for more details.
     try {
       hConnections[ThreadLocalRandom.current().nextInt(noOfConnections)].processBatchCallback(
         actions, tableName, this.batchPool, results, callback);
     } catch (InterruptedException e) {
       throw new InterruptedIOException(e.getMessage());
     }
   }
 
   
   // Copied from HConnectionImplementation.getBatchPool()
   // We should get rid of this when HConnection.processBatchCallback is un-deprecated and provides
   // an API to manage a batch pool
   private void createBatchPool(Configuration conf) {
     // Use the same config for keep alive as in HConnectionImplementation.getBatchPool();
     int maxThreads = conf.getInt("hbase.multihconnection.threads.max", 256);
     int coreThreads = conf.getInt("hbase.multihconnection.threads.core", 256);
     if (maxThreads == 0) {
       maxThreads = Runtime.getRuntime().availableProcessors() * 8;
     }
     if (coreThreads == 0) {
       coreThreads = Runtime.getRuntime().availableProcessors() * 8;
     }
     long keepAliveTime = conf.getLong("hbase.multihconnection.threads.keepalivetime", 60);
     LinkedBlockingQueue<Runnable> workQueue =
         new LinkedBlockingQueue<Runnable>(maxThreads
             * conf.getInt(HConstants.HBASE_CLIENT_MAX_TOTAL_TASKS,
               HConstants.DEFAULT_HBASE_CLIENT_MAX_TOTAL_TASKS));
     ThreadPoolExecutor tpe =
         new ThreadPoolExecutor(coreThreads, maxThreads, keepAliveTime, TimeUnit.SECONDS, workQueue,
             Threads.newDaemonThreadFactory("MultiHConnection" + "-shared-"));
     tpe.allowCoreThreadTimeOut(true);
     this.batchPool = tpe;
   }
   
 }