package org.eclipse.webdav.http.client;

import java.util.Vector;
import org.eclipse.webdav.internal.kernel.utils.Assert;

/**
 * A <code>BufferPool</code> holds on to a collection of buffers (byte
 * arrays) so they can be reused without having to allocate and release
 * memory.
 * <p>
 * <b>Note:</b> This class/interface is part of an interim API that is still under 
 * development and expected to change significantly before reaching stability. 
 * It is being made available at this early stage to solicit feedback from pioneering 
 * adopters on the understanding that any code that uses this API will almost 
 * certainly be broken (repeatedly) as the API evolves.
 * </p>
 */
public class BufferPool {
    /**
     * The size of each buffer in the pool.
     */
    private static int BUFFER_SIZE = 8 * 1024;

    /**
     * The maximum number of buffers in the pool.
     */
    private static int MAX_BUFFERS = 5;

    /**
     * The buffer pool.
     */
    private Vector pool = new Vector(MAX_BUFFERS);

    /**
     * Returns a buffer (byte array) of size <code>BUFFER_SIZE</code> from the
     * pool. When the buffer is no longer needed, it should be put back in the
     * pool for future use by calling <code>putBuffer</code>.
     *
     * @return a buffer
     * @see #putBuffer(byte[])
     */
    public synchronized byte[] getBuffer() {
        if (pool.isEmpty())
            return new byte[BUFFER_SIZE];
        byte[] buffer = (byte[]) pool.lastElement();
        pool.removeElementAt(pool.size() - 1);
        return buffer;
    }

    /**
     * Puts the given buffer into the pool for future use. The size of the
     * buffer must be <code>BUFFER_SIZE</code>.
     *
     * @param buffer the buffer to be put back into the buffer pool
     * @see #getBuffer()
     */
    public synchronized void putBuffer(byte[] buffer) {
        Assert.isNotNull(buffer);
        Assert.isTrue(buffer.length == BUFFER_SIZE);
        if (pool.size() < MAX_BUFFERS)
            pool.addElement(buffer);
    }
}
