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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
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package org.apache.hadoop.hbase.io.hfile;

import org.apache.hadoop.hbase.io.HeapSize;
import org.apache.hadoop.hbase.util.Bytes;
import org.apache.hadoop.hbase.util.ClassSize;
import org.apache.yetus.audience.InterfaceAudience;

/**
 * Represents an entry in the {@link LruBlockCache}.
 * 

* 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 { 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; } } /** Returns Time we were cached at in nano seconds. */ public long getCachedTime() { return this.cachedTime; } @Override 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; } }





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