org.apache.hadoop.hbase.io.hfile.CachedBlockQueue.java Source code

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Here is the source code for org.apache.hadoop.hbase.io.hfile.CachedBlockQueue.java

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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 com.google.common.collect.MinMaxPriorityQueue;

import org.apache.hadoop.classification.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.
 *
 * <p>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.
 *
 * <p>Object used in this queue must implement {@link HeapSize} as well as
 * {@link Comparable}.
 */
@InterfaceAudience.Private
public class CachedBlockQueue implements HeapSize {

    private MinMaxPriorityQueue<CachedBlock> 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 CachedBlockQueue(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.
     *
     * <p>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(CachedBlock cb) {
        if (heapSize < maxSize) {
            queue.add(cb);
            heapSize += cb.heapSize();
        } else {
            CachedBlock 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 CachedBlock poll() {
        return queue.poll();
    }

    /**
     * @return The last element in this queue, or {@code null} if the queue is
     * empty.
     */
    public CachedBlock pollLast() {
        return queue.pollLast();
    }

    /**
     * Total size of all elements in this queue.
     * @return size of all elements currently in queue, in bytes
     */
    public long heapSize() {
        return heapSize;
    }
}