org.apache.hadoop.io.ElasticByteBufferPool.java Source code

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Here is the source code for org.apache.hadoop.io.ElasticByteBufferPool.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.io;

import com.google.common.collect.ComparisonChain;
import org.apache.commons.lang.builder.HashCodeBuilder;

import java.nio.ByteBuffer;
import java.util.Map;
import java.util.TreeMap;

import org.apache.hadoop.classification.InterfaceAudience;
import org.apache.hadoop.classification.InterfaceStability;

/**
 * This is a simple ByteBufferPool which just creates ByteBuffers as needed.
 * It also caches ByteBuffers after they're released.  It will always return
 * the smallest cached buffer with at least the capacity you request.
 * We don't try to do anything clever here like try to limit the maximum cache
 * size.
 */
@InterfaceAudience.Public
@InterfaceStability.Stable
public final class ElasticByteBufferPool implements ByteBufferPool {
    private static final class Key implements Comparable<Key> {
        private final int capacity;
        private final long insertionTime;

        Key(int capacity, long insertionTime) {
            this.capacity = capacity;
            this.insertionTime = insertionTime;
        }

        @Override
        public int compareTo(Key other) {
            return ComparisonChain.start().compare(capacity, other.capacity)
                    .compare(insertionTime, other.insertionTime).result();
        }

        @Override
        public boolean equals(Object rhs) {
            if (rhs == null) {
                return false;
            }
            try {
                Key o = (Key) rhs;
                return (compareTo(o) == 0);
            } catch (ClassCastException e) {
                return false;
            }
        }

        @Override
        public int hashCode() {
            return new HashCodeBuilder().append(capacity).append(insertionTime).toHashCode();
        }
    }

    private final TreeMap<Key, ByteBuffer> buffers = new TreeMap<Key, ByteBuffer>();

    private final TreeMap<Key, ByteBuffer> directBuffers = new TreeMap<Key, ByteBuffer>();

    private final TreeMap<Key, ByteBuffer> getBufferTree(boolean direct) {
        return direct ? directBuffers : buffers;
    }

    @Override
    public synchronized ByteBuffer getBuffer(boolean direct, int length) {
        TreeMap<Key, ByteBuffer> tree = getBufferTree(direct);
        Map.Entry<Key, ByteBuffer> entry = tree.ceilingEntry(new Key(length, 0));
        if (entry == null) {
            return direct ? ByteBuffer.allocateDirect(length) : ByteBuffer.allocate(length);
        }
        tree.remove(entry.getKey());
        return entry.getValue();
    }

    @Override
    public synchronized void putBuffer(ByteBuffer buffer) {
        TreeMap<Key, ByteBuffer> tree = getBufferTree(buffer.isDirect());
        while (true) {
            Key key = new Key(buffer.capacity(), System.nanoTime());
            if (!tree.containsKey(key)) {
                tree.put(key, buffer);
                return;
            }
            // Buffers are indexed by (capacity, time).
            // If our key is not unique on the first try, we try again, since the
            // time will be different.  Since we use nanoseconds, it's pretty
            // unlikely that we'll loop even once, unless the system clock has a
            // poor granularity.
        }
    }
}