ByteArrayPool.java

/*
 *  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.mina.util.byteaccess;

import java.util.ArrayList;
import java.util.Stack;

import org.apache.mina.core.buffer.IoBuffer;

/**
 * Creates <code>ByteArray</code>s, using a pool to reduce allocation where possible.
 *
 * WARNING: This code has never been run!
 * 
 *
 * @author <a href="http://mina.apache.org">Apache MINA Project</a>
 */
public class ByteArrayPool implements ByteArrayFactory {

    private final int MAX_BITS = 32;

    private boolean freed;

    private final boolean direct;

    private ArrayList<Stack<DirectBufferByteArray>> freeBuffers;

    private int freeBufferCount = 0;

    private long freeMemory = 0;

    private final int maxFreeBuffers;

    private final int maxFreeMemory;

    /**
     * Creates a new instance of ByteArrayPool.
     *
     * @param direct
     *  If we should use direct buffers
     * @param maxFreeBuffers
     *  The maximum number of free buffers
     * @param maxFreeMemory
     *  The maximum amount of free memory allowed
     */
    public ByteArrayPool(boolean direct, int maxFreeBuffers, int maxFreeMemory) {
        this.direct = direct;
        freeBuffers = new ArrayList<Stack<DirectBufferByteArray>>();
        for (int i = 0; i < MAX_BITS; i++) {
            freeBuffers.add(new Stack<DirectBufferByteArray>());
        }
        this.maxFreeBuffers = maxFreeBuffers;
        this.maxFreeMemory = maxFreeMemory;
        this.freed = false;
    }

    /**
     * Creates a new instance of a {@link ByteArray}
     * 
     * @param size
     *  The size of the array to build
     */
    public ByteArray create(int size) {
        if (size < 1) {
            throw new IllegalArgumentException("Buffer size must be at least 1: " + size);
        }
        int bits = bits(size);
        synchronized (this) {
            if (!freeBuffers.get(bits).isEmpty()) {
                DirectBufferByteArray ba = freeBuffers.get(bits).pop();
                ba.setFreed(false);
                ba.getSingleIoBuffer().limit(size);
                return ba;
            }
        }
        IoBuffer bb;
        int bbSize = 1 << bits;
        bb = IoBuffer.allocate(bbSize, direct);
        bb.limit(size);
        DirectBufferByteArray ba = new DirectBufferByteArray(bb);
        ba.setFreed(false);
        return ba;
    }

    private int bits(int index) {
        int bits = 0;
        while (1 << bits < index) {
            bits++;
        }
        return bits;
    }

    /**
     * Frees the buffers
     *
     */
    public void free() {
        synchronized (this) {
            if (freed) {
                throw new IllegalStateException("Already freed.");
            }
            freed = true;
            freeBuffers.clear();
            freeBuffers = null;
        }
    }

    private class DirectBufferByteArray extends BufferByteArray {

        private boolean freed;

        public DirectBufferByteArray(IoBuffer bb) {
            super(bb);
        }

        public void setFreed(boolean freed) {
            this.freed = freed;
        }

        @Override
        public void free() {
            synchronized (this) {
                if (freed) {
                    throw new IllegalStateException("Already freed.");
                }
                freed = true;
            }
            int bits = bits(last());
            synchronized (ByteArrayPool.this) {
                if (freeBuffers != null && freeBufferCount < maxFreeBuffers && freeMemory + last() <= maxFreeMemory) {
                    freeBuffers.get(bits).push(this);
                    freeBufferCount++;
                    freeMemory += last();
                    return;
                }
            }
        }

    }

}