PacketAllocator.java

/*
 * PacketAllocator.java February 2008
 *
 * Copyright (C) 2008, Niall Gallagher <niallg@users.sf.net>
 *
 * Licensed 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.simpleframework.transport;

import java.nio.ByteBuffer;
import java.util.concurrent.atomic.AtomicLong;

/**
 * The <code>PacketAllocator</code> object is used to create packets that
 * contain increasing sequence numbers. This acts as a pool for buffers which
 * can be recycled by closing the <code>Packet</code> objects created by this
 * allocator. As well as creating buffers from a pool of byte buffers this can
 * wrap an existing buffer within a packet so it can be used uniformly.
 * 
 * @author Niall Gallagher
 */
class PacketAllocator {

    /**
     * This is the memory manager used to recycle the buffers.
     */
    private final PacketManager manager;

    /**
     * This is the counter used to generate the sequence numbers.
     */
    private final AtomicLong count;

    /**
     * Constructor for the <code>PacketAllocator</code> object. This is provided
     * the size of the buffers that will be allocated and the number of buffers
     * that can be lazily created before it will block waiting for the next
     * buffer to be returned.
     */
    public PacketAllocator() {
        this(3);
    }

    /**
     * Constructor for the <code>PacketAllocator</code> object. This is provided
     * the size of the buffers that will be allocated and the number of buffers
     * that can be lazily created before it will block waiting for the next
     * buffer to be returned.
     * 
     * @param allow
     *            this is the queue size for asynchronous writes
     */
    public PacketAllocator(int allow) {
        this(allow, 4096);
    }

    /**
     * Constructor for the <code>PacketAllocator</code> object. This is provided
     * the size of the buffers that will be allocated and the number of buffers
     * that can be lazily created before it will block waiting for the next
     * buffer to be returned.
     * 
     * @param allow
     *            this is the queue size for asynchronous writes
     * @param size
     *            this is the size of the buffers to be allocated
     */
    public PacketAllocator(int allow, int size) {
        this.manager = new PacketManager(allow, size);
        this.count = new AtomicLong();
    }

    /**
     * This creates a <code>Packet</code> from a buffer within the pool of
     * buffers. The buffer provided can be modified up until such point as it is
     * recycled. To recycle the buffer the packet must be closed, when closed
     * the buffer can be reused.
     * 
     * @return this returns a packet backed by a pooled buffer
     */
    public Packet allocate() throws PacketException {
        long sequence = this.count.getAndIncrement();
        ByteBuffer buffer = this.manager.allocate();

        return new Appender(buffer, this.manager, sequence);
    }

    /**
     * This creates a <code>Packet</code> by wrapping the provided buffer within
     * the packet interface. The buffer provided will be read only such that the
     * buffer it wraps is not modified.
     * 
     * @param buffer
     *            this is the buffer that has been wrapped
     * 
     * @return this returns a packet backed by a pooled buffer
     */
    public Packet allocate(ByteBuffer buffer) throws PacketException {
        long sequence = this.count.getAndIncrement();

        return new Wrapper(buffer, sequence);
    }
}