/**
    *
    * 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.io.hfile;
  
  import org.apache.hadoop.hbase.classification.InterfaceAudience;
  import org.apache.hadoop.hbase.io.HeapSize;
  import org.apache.hadoop.hbase.util.Bytes;
  import org.apache.hadoop.hbase.util.ClassSize;
  
  /**
   * Represents an entry in the {@link LruBlockCache}.
   *
   * <p>Makes the block memory-aware with {@link HeapSize} and Comparable
   * to sort by access time for the LRU.  It also takes care of priority by
   * either instantiating as in-memory or handling the transition from single
   * to multiple access.
   */
  @InterfaceAudience.Private
  public class LruCachedBlock implements HeapSize, Comparable<LruCachedBlock> {
  
    public final static long PER_BLOCK_OVERHEAD = ClassSize.align(
      ClassSize.OBJECT + (3 * ClassSize.REFERENCE) + (3 * Bytes.SIZEOF_LONG) +
      ClassSize.STRING + ClassSize.BYTE_BUFFER);
  
    private final BlockCacheKey cacheKey;
    private final Cacheable buf;
    private volatile long accessTime;
    private long size;
    private BlockPriority priority;
    /**
     * Time this block was cached.  Presumes we are created just before we are added to the cache.
     */
    private final long cachedTime = System.nanoTime();
  
    public LruCachedBlock(BlockCacheKey cacheKey, Cacheable buf, long accessTime) {
      this(cacheKey, buf, accessTime, false);
    }
  
    public LruCachedBlock(BlockCacheKey cacheKey, Cacheable buf, long accessTime,
        boolean inMemory) {
      this.cacheKey = cacheKey;
      this.buf = buf;
      this.accessTime = accessTime;
      // We approximate the size of this class by the size of its name string
      // plus the size of its byte buffer plus the overhead associated with all
      // the base classes. We also include the base class
      // sizes in the PER_BLOCK_OVERHEAD variable rather than align()ing them with
      // their buffer lengths. This variable is used elsewhere in unit tests.
      this.size = ClassSize.align(cacheKey.heapSize())
          + ClassSize.align(buf.heapSize()) + PER_BLOCK_OVERHEAD;
      if(inMemory) {
        this.priority = BlockPriority.MEMORY;
      } else {
        this.priority = BlockPriority.SINGLE;
      }
    }
  
    /**
     * Block has been accessed.
     * @param accessTime Last access; this is actually a incremented sequence number rather than an
     * actual time.
     */
    public void access(long accessTime) {
      this.accessTime = accessTime;
      if(this.priority == BlockPriority.SINGLE) {
        this.priority = BlockPriority.MULTI;
      }
    }
  
    /**
     * @return Time we were cached at in nano seconds.
     */
    public long getCachedTime() {
      return this.cachedTime;
    }
  
    public long heapSize() {
      return size;
    }
  
    @Override
    public int compareTo(LruCachedBlock that) {
      // Newer accessed blocks sort before older ones.
     if (this.accessTime == that.accessTime) return 0;
     return this.accessTime < that.accessTime ? 1 : -1;
   }
 
   @Override
   public int hashCode() {
     return (int)(accessTime ^ (accessTime >>> 32));
   }
 
   @Override
   public boolean equals(Object obj) {
     if (this == obj) {
       return true;
     }
     if (obj == null || getClass() != obj.getClass()) {
       return false;
     }
     LruCachedBlock other = (LruCachedBlock) obj;
     return compareTo(other) == 0;
   }
 
   public Cacheable getBuffer() {
     return this.buf;
   }
 
   public BlockCacheKey getCacheKey() {
     return this.cacheKey;
   }
 
   public BlockPriority getPriority() {
     return this.priority;
   }
 }