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/**
 * 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.ipc;

import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.BlockingQueue;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.concurrent.ThreadLocalRandom;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.hadoop.hbase.classification.InterfaceAudience;
import org.apache.hadoop.hbase.classification.InterfaceStability;

import com.google.common.base.Preconditions;
import com.google.common.base.Strings;

@InterfaceAudience.Private
@InterfaceStability.Evolving
public abstract class RpcExecutor {
  private static final Log LOG = LogFactory.getLog(RpcExecutor.class);

  private final AtomicInteger activeHandlerCount = new AtomicInteger(0);
  private final List handlers;
  private final int handlerCount;
  private final String name;

  private boolean running;

  public RpcExecutor(final String name, final int handlerCount) {
    this.handlers = new ArrayList(handlerCount);
    this.handlerCount = handlerCount;
    this.name = Strings.nullToEmpty(name);
  }

  public void start(final int port) {
    running = true;
    startHandlers(port);
  }

  public void stop() {
    running = false;
    for (Thread handler : handlers) {
      handler.interrupt();
    }
  }

  public int getActiveHandlerCount() {
    return activeHandlerCount.get();
  }

  /** Returns the length of the pending queue */
  public abstract int getQueueLength();

  /** Add the request to the executor queue */
  public abstract void dispatch(final CallRunner callTask) throws InterruptedException;

  /** Returns the list of request queues */
  protected abstract List> getQueues();

  protected void startHandlers(final int port) {
    List> callQueues = getQueues();
    startHandlers(null, handlerCount, callQueues, 0, callQueues.size(), port);
  }

  protected void startHandlers(final String nameSuffix, final int numHandlers,
      final List> callQueues,
      final int qindex, final int qsize, final int port) {
    final String threadPrefix = name + Strings.nullToEmpty(nameSuffix);
    for (int i = 0; i < numHandlers; i++) {
      final int index = qindex + (i % qsize);
      Thread t = new Thread(new Runnable() {
        @Override
        public void run() {
          consumerLoop(callQueues.get(index));
        }
      });
      t.setDaemon(true);
      t.setName(threadPrefix + "RpcServer.handler=" + handlers.size() +
          ",queue=" + index + ",port=" + port);
      t.start();
      LOG.debug(threadPrefix + " Start Handler index=" + handlers.size() + " queue=" + index);
      handlers.add(t);
    }
  }

  protected void consumerLoop(final BlockingQueue myQueue) {
    boolean interrupted = false;
    try {
      while (running) {
        try {
          CallRunner task = myQueue.take();
          try {
            activeHandlerCount.incrementAndGet();
            task.run();
          } catch (Throwable t) {
            LOG.error("RpcServer handler thread throws exception: ", t);
            throw t;
          } finally {
            activeHandlerCount.decrementAndGet();
          }
        } catch (InterruptedException e) {
          interrupted = true;
        }
      }
    } finally {
      if (interrupted) {
        Thread.currentThread().interrupt();
      }
    }
  }

  public static abstract class QueueBalancer {
    /**
     * @return the index of the next queue to which a request should be inserted
     */
    public abstract int getNextQueue();
  }

  public static QueueBalancer getBalancer(int queueSize) {
    Preconditions.checkArgument(queueSize > 0, "Queue size is <= 0, must be at least 1");
    if (queueSize == 1) {
      return ONE_QUEUE;
    } else {
      return new RandomQueueBalancer(queueSize);
    }
  }

  /**
   * All requests go to the first queue, at index 0
   */
  private static QueueBalancer ONE_QUEUE = new QueueBalancer() {

    @Override
    public int getNextQueue() {
      return 0;
    }
  };

  /**
   * Queue balancer that just randomly selects a queue in the range [0, num queues).
   */
  private static class RandomQueueBalancer extends QueueBalancer {
    private final int queueSize;

    public RandomQueueBalancer(int queueSize) {
      this.queueSize = queueSize;
    }

    public int getNextQueue() {
      return ThreadLocalRandom.current().nextInt(queueSize);
    }
  }
}