/*
    *
    * 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.namequeues;
  
  import com.google.common.base.Preconditions;
  import com.lmax.disruptor.BlockingWaitStrategy;
  import com.lmax.disruptor.EventFactory;
  import com.lmax.disruptor.RingBuffer;
  import com.lmax.disruptor.dsl.Disruptor;
  import com.lmax.disruptor.dsl.ProducerType;
  import java.util.concurrent.Executors;
  import org.apache.hadoop.conf.Configuration;
  import org.apache.hadoop.hbase.classification.InterfaceAudience;
  import org.apache.hadoop.hbase.classification.InterfaceStability;
  import org.apache.hadoop.hbase.namequeues.request.NamedQueueGetRequest;
  import org.apache.hadoop.hbase.namequeues.response.NamedQueueGetResponse;
  import org.apache.hadoop.hbase.util.Threads;
  
  /**
   * NamedQueue recorder that maintains various named queues.
   * The service uses LMAX Disruptor to save queue records which are then consumed by
   * a queue and based on the ring buffer size, the available records are then fetched
   * from the queue in thread-safe manner.
   */
  @InterfaceAudience.Private
  @InterfaceStability.Evolving
  public final class NamedQueueRecorder {
  
    private final Disruptor<RingBufferEnvelope> disruptor;
    private final LogEventHandler logEventHandler;
  
    private static NamedQueueRecorder namedQueueRecorder;
    private static boolean isInit = false;
    private static final Object LOCK = new Object();
  
    /**
     * Initialize disruptor with configurable ringbuffer size
     */
    private NamedQueueRecorder(Configuration conf) {
  
      // This is the 'writer' -- a single threaded executor. This single thread consumes what is
      // put on the ringbuffer.
      final String hostingThreadName = Thread.currentThread().getName();
  
      int eventCount = conf.getInt("hbase.namedqueue.ringbuffer.size", 1024);
  
      // disruptor initialization with BlockingWaitStrategy
      this.disruptor = new Disruptor<>(getEventFactory(), getEventCount(eventCount), Executors.
        newSingleThreadExecutor(Threads.getNamedThreadFactory(hostingThreadName
          + ".slowlog.append-pool")),
        ProducerType.MULTI, new BlockingWaitStrategy());
      this.disruptor.handleExceptionsWith(new DisruptorExceptionHandler());
  
      // initialize ringbuffer event handler
      this.logEventHandler = new LogEventHandler(conf);
      this.disruptor.handleEventsWith(new LogEventHandler[]{this.logEventHandler});
      this.disruptor.start();
    }
  
    private EventFactory<RingBufferEnvelope> getEventFactory() {
      return new EventFactory<RingBufferEnvelope>() {
        @Override
        public RingBufferEnvelope newInstance() {
          return new RingBufferEnvelope();
        }
      };
    }
  
    public static NamedQueueRecorder getInstance(Configuration conf) {
      if (namedQueueRecorder != null) {
        return namedQueueRecorder;
      }
      synchronized (LOCK) {
        if (!isInit) {
          namedQueueRecorder = new NamedQueueRecorder(conf);
          isInit = true;
        }
      }
      return namedQueueRecorder;
    }
  
    // must be power of 2 for disruptor ringbuffer
   private int getEventCount(int eventCount) {
     Preconditions.checkArgument(eventCount >= 0, "hbase.namedqueue.ringbuffer.size must be > 0");
     int floor = Integer.highestOneBit(eventCount);
     if (floor == eventCount) {
       return floor;
     }
     // max capacity is 1 << 30
     if (floor >= 1 << 29) {
       return 1 << 30;
     }
     return floor << 1;
   }
 
   /**
    * Retrieve in memory queue records from ringbuffer
    *
    * @param request namedQueue request with event type
    * @return queue records from ringbuffer after filter (if applied)
    */
   public NamedQueueGetResponse getNamedQueueRecords(NamedQueueGetRequest request) {
     return this.logEventHandler.getNamedQueueRecords(request);
   }
 
   /**
    * clears queue records from ringbuffer
    *
    * @param namedQueueEvent type of queue to clear
    * @return true if slow log payloads are cleaned up or
    *   hbase.regionserver.slowlog.buffer.enabled is not set to true, false if failed to
    *   clean up slow logs
    */
   public boolean clearNamedQueue(NamedQueuePayload.NamedQueueEvent namedQueueEvent) {
     return this.logEventHandler.clearNamedQueue(namedQueueEvent);
   }
 
   /**
    * Add various NamedQueue records to ringbuffer. Based on the type of the event (e.g slowLog),
    * consumer of disruptor ringbuffer will have specific logic.
    * This method is producer of disruptor ringbuffer which is initialized in NamedQueueRecorder
    * constructor.
    *
    * @param namedQueuePayload namedQueue payload sent by client of ring buffer
    *   service
    */
   public void addRecord(NamedQueuePayload namedQueuePayload) {
     RingBuffer<RingBufferEnvelope> ringBuffer = this.disruptor.getRingBuffer();
     long seqId = ringBuffer.next();
     try {
       ringBuffer.get(seqId).load(namedQueuePayload);
     } finally {
       ringBuffer.publish(seqId);
     }
   }
 
   /**
    * Add all in memory queue records to system table. The implementors can use system table
    * or direct HDFS file or ZK as persistence system.
    */
   public void persistAll(NamedQueuePayload.NamedQueueEvent namedQueueEvent) {
     if (this.logEventHandler != null) {
       this.logEventHandler.persistAll(namedQueueEvent);
     }
   }
 
 }