/*
* Copyright 2004-2011 H2 Group. Multiple-Licensed under the H2 License,
* Version 1.0, and under the Eclipse Public License, Version 1.0
* (http://h2database.com/html/license.html).
* Initial Developer: H2 Group
*/
package org.h2.store;
import org.h2.engine.Session;
import org.h2.util.BitField;
/**
* The list of free pages of a page store. The format of a free list trunk page
* is:
* <ul>
* <li>page type: byte (0)</li>
* <li>checksum: short (1-2)</li>
* <li>data (3-)</li>
* </ul>
*/
public class PageFreeList extends Page {
private static final int DATA_START = 3;
private final PageStore store;
private final BitField used;
private final int pageCount;
private boolean full;
private Data data;
private PageFreeList(PageStore store, int pageId) {
// kept in cache, and array list in page store
setPos(pageId);
this.store = store;
pageCount = (store.getPageSize() - DATA_START) * 8;
used = new BitField(pageCount);
used.set(0);
}
/**
* Read a free-list page.
*
* @param store the page store
* @param data the data
* @param pageId the page id
* @return the page
*/
static PageFreeList read(PageStore store, Data data, int pageId) {
PageFreeList p = new PageFreeList(store, pageId);
p.data = data;
p.read();
return p;
}
/**
* Create a new free-list page.
*
* @param store the page store
* @param pageId the page id
* @return the page
*/
static PageFreeList create(PageStore store, int pageId) {
return new PageFreeList(store, pageId);
}
/**
* Allocate a page from the free list.
*
* @param exclude the exclude list or null
* @param first the first page to look for
* @return the page, or -1 if all pages are used
*/
int allocate(BitField exclude, int first) {
if (full) {
return -1;
}
// TODO cache last result
int start = Math.max(0, first - getPos());
while (true) {
int free = used.nextClearBit(start);
if (free >= pageCount) {
if (start == 0) {
full = true;
}
return -1;
}
if (exclude != null && exclude.get(free + getPos())) {
start = exclude.nextClearBit(free + getPos()) - getPos();
if (start >= pageCount) {
return -1;
}
} else {
// set the bit first, because logUndo can
// allocate other pages, and we must not
// return the same page twice
used.set(free);
store.logUndo(this, data);
store.update(this);
return free + getPos();
}
}
}
/**
* Get the first free page starting at the given offset.
*
* @param first the page number to start the search
* @return the page number, or -1
*/
int getFirstFree(int first) {
if (full) {
return -1;
}
int start = Math.max(0, first - getPos());
int free = used.nextClearBit(start);
if (free >= pageCount) {
return -1;
}
return free + getPos();
}
int getLastUsed() {
int last = used.length() - 1;
return last <= 0 ? -1 : last + getPos();
}
/**
* Mark a page as used.
*
* @param pageId the page id
* @return the page id, or -1
*/
int allocate(int pageId) {
int idx = pageId - getPos();
if (idx >= 0 && !used.get(idx)) {
// set the bit first, because logUndo can
// allocate other pages, and we must not
// return the same page twice
used.set(idx);
store.logUndo(this, data);
store.update(this);
}
return pageId;
}
/**
* Add a page to the free list.
*
* @param pageId the page id to add
*/
void free(int pageId) {
full = false;
store.logUndo(this, data);
used.clear(pageId - getPos());
store.update(this);
}
/**
* Read the page from the disk.
*/
private void read() {
data.reset();
data.readByte();
data.readShortInt();
for (int i = 0; i < pageCount; i += 8) {
int x = data.readByte() & 255;
used.setByte(i, x);
}
full = false;
}
public void write() {
data = store.createData();
data.writeByte((byte) Page.TYPE_FREE_LIST);
data.writeShortInt(0);
for (int i = 0; i < pageCount; i += 8) {
data.writeByte((byte) used.getByte(i));
}
store.writePage(getPos(), data);
}
/**
* Get the number of pages that can fit in a free list.
*
* @param pageSize the page size
* @return the number of pages
*/
public static int getPagesAddressed(int pageSize) {
return (pageSize - DATA_START) * 8;
}
/**
* Get the estimated memory size.
*
* @return number of double words (4 bytes)
*/
public int getMemory() {
return store.getPageSize() >> 2;
}
/**
* Check if a page is already in use.
*
* @param pageId the page to check
* @return true if it is in use
*/
boolean isUsed(int pageId) {
return used.get(pageId - getPos());
}
public void moveTo(Session session, int newPos) {
// the old data does not need to be copied, as free-list pages
// at the end of the file are not required
store.free(getPos(), false);
}
public String toString() {
return "page [" + getPos() + "] freeList" + (full ? "full" : "");
}
public boolean canRemove() {
return true;
}
public boolean canMove() {
return false;
}
}