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/*
Copyright (c) 2008 Health Market Science, Inc.
This library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
This library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with this library; if not, write to the Free Software
Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307
USA
You can contact Health Market Science at info@healthmarketscience.com
or at the following address:
Health Market Science
2700 Horizon Drive
Suite 200
King of Prussia, PA 19406
*/
package com.healthmarketscience.jackcess;
import java.lang.ref.Reference;
import java.lang.ref.SoftReference;
import java.nio.ByteBuffer;
import java.nio.ByteOrder;
/**
* Manages a reference to a ByteBuffer.
*
* @author James Ahlborn
*/
public abstract class TempBufferHolder {
private static final Reference<ByteBuffer> EMPTY_BUFFER_REF =
new SoftReference<ByteBuffer>(null);
/**
* The caching type for the buffer holder.
*/
public enum Type {
/** a hard reference is maintained to the created buffer */
HARD,
/** a soft reference is maintained to the created buffer (may be garbage
collected if memory gets tight) */
SOFT,
/** no reference is maintained to a created buffer (new buffer every
time) */
NONE;
}
/** whether or not every get automatically rewinds the buffer */
private final boolean _autoRewind;
/** ByteOrder for all allocated buffers */
private final ByteOrder _order;
/** the mod count of the current buffer (changes on every realloc) */
private int _modCount;
protected TempBufferHolder(boolean autoRewind, ByteOrder order) {
_autoRewind = autoRewind;
_order = order;
}
/**
* @return the modification count of the current buffer (this count is
* changed every time the buffer is reallocated)
*/
public int getModCount() {
return _modCount;
}
/**
* Creates a new TempBufferHolder.
* @param type the type of reference desired for any created buffer
* @param autoRewind whether or not every get automatically rewinds the
* buffer
*/
public static TempBufferHolder newHolder(Type type, boolean autoRewind) {
return newHolder(type, autoRewind, PageChannel.DEFAULT_BYTE_ORDER);
}
/**
* Creates a new TempBufferHolder.
* @param type the type of reference desired for any created buffer
* @param autoRewind whether or not every get automatically rewinds the
* buffer
* @param order byte order for all allocated buffers
*/
public static TempBufferHolder newHolder(Type type, boolean autoRewind,
ByteOrder order)
{
switch(type) {
case HARD:
return new HardTempBufferHolder(autoRewind, order);
case SOFT:
return new SoftTempBufferHolder(autoRewind, order);
case NONE:
return new NoneTempBufferHolder(autoRewind, order);
default:
throw new IllegalStateException("Unknown type " + type);
}
}
/**
* Returns a ByteBuffer of at least the defined page size, with the limit
* set to the page size, and the predefined byteOrder. Will be rewound iff
* autoRewind is enabled for this buffer.
*/
public final ByteBuffer getPageBuffer(PageChannel pageChannel) {
return getBuffer(pageChannel, pageChannel.getFormat().PAGE_SIZE);
}
/**
* Returns a ByteBuffer of at least the given size, with the limit set to
* the given size, and the predefined byteOrder. Will be rewound iff
* autoRewind is enabled for this buffer.
*/
public final ByteBuffer getBuffer(PageChannel pageChannel, int size) {
ByteBuffer buffer = getExistingBuffer();
if((buffer == null) || (buffer.capacity() < size)) {
buffer = pageChannel.createBuffer(size, _order);
++_modCount;
setNewBuffer(buffer);
} else {
buffer.limit(size);
}
if(_autoRewind) {
buffer.rewind();
}
return buffer;
}
/**
* @return the currently referenced buffer, {@code null} if none
*/
public abstract ByteBuffer getExistingBuffer();
/**
* Releases any referenced memory.
*/
public abstract void clear();
/**
* Sets a new buffer for this holder.
*/
protected abstract void setNewBuffer(ByteBuffer newBuffer);
/**
* TempBufferHolder which has a hard reference to the buffer.
*/
private static final class HardTempBufferHolder extends TempBufferHolder
{
private ByteBuffer _buffer;
private HardTempBufferHolder(boolean autoRewind, ByteOrder order) {
super(autoRewind, order);
}
@Override
public ByteBuffer getExistingBuffer() {
return _buffer;
}
@Override
protected void setNewBuffer(ByteBuffer newBuffer) {
_buffer = newBuffer;
}
@Override
public void clear() {
_buffer = null;
}
}
/**
* TempBufferHolder which has a soft reference to the buffer.
*/
private static final class SoftTempBufferHolder extends TempBufferHolder
{
private Reference<ByteBuffer> _buffer = EMPTY_BUFFER_REF;
private SoftTempBufferHolder(boolean autoRewind, ByteOrder order) {
super(autoRewind, order);
}
@Override
public ByteBuffer getExistingBuffer() {
return _buffer.get();
}
@Override
protected void setNewBuffer(ByteBuffer newBuffer) {
_buffer.clear();
_buffer = new SoftReference<ByteBuffer>(newBuffer);
}
@Override
public void clear() {
_buffer.clear();
}
}
/**
* TempBufferHolder which has a no reference to the buffer.
*/
private static final class NoneTempBufferHolder extends TempBufferHolder
{
private NoneTempBufferHolder(boolean autoRewind, ByteOrder order) {
super(autoRewind, order);
}
@Override
public ByteBuffer getExistingBuffer() {
return null;
}
@Override
protected void setNewBuffer(ByteBuffer newBuffer) {
// nothing to do
}
@Override
public void clear() {
// nothing to do
}
}
}
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