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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.io.hfile;

import org.apache.hbase.thirdparty.com.google.common.collect.MinMaxPriorityQueue;

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

/**
 * A memory-bound queue that will grow until an element brings
 * total size >= maxSize.  From then on, only entries that are sorted larger
 * than the smallest current entry will be inserted/replaced.
 *
 * 

Use this when you want to find the largest elements (according to their * ordering, not their heap size) that consume as close to the specified * maxSize as possible. Default behavior is to grow just above rather than * just below specified max. * *

Object used in this queue must implement {@link HeapSize} as well as * {@link Comparable}. */ @InterfaceAudience.Private public class LruCachedBlockQueue implements HeapSize { private MinMaxPriorityQueue queue; private long heapSize; private long maxSize; /** * @param maxSize the target size of elements in the queue * @param blockSize expected average size of blocks */ public LruCachedBlockQueue(long maxSize, long blockSize) { int initialSize = (int)(maxSize / blockSize); if(initialSize == 0) initialSize++; queue = MinMaxPriorityQueue.expectedSize(initialSize).create(); heapSize = 0; this.maxSize = maxSize; } /** * Attempt to add the specified cached block to this queue. * *

If the queue is smaller than the max size, or if the specified element * is ordered before the smallest element in the queue, the element will be * added to the queue. Otherwise, there is no side effect of this call. * @param cb block to try to add to the queue */ public void add(LruCachedBlock cb) { if(heapSize < maxSize) { queue.add(cb); heapSize += cb.heapSize(); } else { LruCachedBlock head = queue.peek(); if(cb.compareTo(head) > 0) { heapSize += cb.heapSize(); heapSize -= head.heapSize(); if(heapSize > maxSize) { queue.poll(); } else { heapSize += head.heapSize(); } queue.add(cb); } } } /** * @return The next element in this queue, or {@code null} if the queue is * empty. */ public LruCachedBlock poll() { return queue.poll(); } /** * @return The last element in this queue, or {@code null} if the queue is * empty. */ public LruCachedBlock pollLast() { return queue.pollLast(); } /** * Total size of all elements in this queue. * @return size of all elements currently in queue, in bytes */ @Override public long heapSize() { return heapSize; } }





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