/*
    *
    * 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.TimeoutException;
  import com.lmax.disruptor.dsl.Disruptor;
  import com.lmax.disruptor.dsl.ProducerType;
  import java.io.Closeable;
  import java.io.IOException;
  import java.util.concurrent.ExecutorService;
  import java.util.concurrent.Executors;
  import java.util.concurrent.TimeUnit;
  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;
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  /**
   * 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 implements Closeable {
    private static final Logger LOG = LoggerFactory.getLogger(NamedQueueRecorder.class);
    private final Disruptor<RingBufferEnvelope> disruptor;
    private final LogEventHandler logEventHandler;
    private final ExecutorService executorService;
  
    private static NamedQueueRecorder namedQueueRecorder;
    private static boolean isInit = false;
    private static final Object LOCK = new Object();
    private volatile boolean closed = false;
  
    /**
     * 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);
  
      this.executorService = Executors.newSingleThreadExecutor(Threads.getNamedThreadFactory(
        hostingThreadName + ".slowlog.append-pool"));
      // disruptor initialization with BlockingWaitStrategy
      this.disruptor = new Disruptor<>(getEventFactory(), getEventCount(eventCount), executorService,
        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) {
     if (!closed) {
       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);
     }
   }
 
   @Override
   public void close() throws IOException {
     // Setting closed flag to true so that we don't add more events to RingBuffer.
     this.closed = true;
     LOG.info("Closing NamedQueueRecorder");
     if (this.disruptor != null) {
       long timeoutms = 5000;
       try {
         this.disruptor.shutdown(timeoutms, TimeUnit.MILLISECONDS);
       } catch (TimeoutException e) {
         LOG.warn("Timed out bringing down disruptor after " + timeoutms + " ms; forcing halt", e);
         this.disruptor.halt();
         this.disruptor.shutdown();
       }
     }
     // With disruptor down, this is safe to let go.
     if (this.executorService !=  null) {
       // This will close the executor threads.
       this.executorService.shutdownNow();
     }
   }
 }