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/*
* Copyright 2004-2019 H2 Group. Multiple-Licensed under the MPL 2.0,
* and the EPL 1.0 (https://h2database.com/html/license.html).
* Initial Developer: H2 Group
*/
package org.h2.pagestore;
import java.util.BitSet;
import org.h2.engine.Session;
import org.h2.store.Data;
/**
* The list of free pages of a page store. The format of a free list trunk page
* is:
*
*
page type: byte (0)
*
checksum: short (1-2)
*
data (3-)
*
*/
public class PageFreeList extends Page {
private static final int DATA_START = 3;
private final PageStore store;
private final BitSet used;
private final int pageCount;
private boolean full;
private Data data;
private PageFreeList(PageStore store, int pageId, int pageCount, BitSet used) {
// kept in cache, and array list in page store
setPos(pageId);
this.store = store;
this.pageCount = pageCount;
this.used = used;
}
/**
* 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) {
data.reset();
data.readByte();
data.readShortInt();
int length = store.getPageSize() - DATA_START;
byte[] b = new byte[length];
data.read(b, 0, b.length);
PageFreeList p = new PageFreeList(store, pageId, length * 8, BitSet.valueOf(b));
p.data = data;
p.full = false;
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) {
int pageCount = (store.getPageSize() - DATA_START) * 8;
BitSet used = new BitSet(pageCount);
used.set(0);
return new PageFreeList(store, pageId, pageCount, used);
}
/**
* 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(BitSet 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
*/
void 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);
}
}
/**
* 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);
}
@Override
public void write() {
data = store.createData();
data.writeByte((byte) Page.TYPE_FREE_LIST);
data.writeShortInt(0);
int cnt = pageCount >>> 3;
byte[] b = used.toByteArray();
int l = Math.min(b.length, cnt);
data.write(b, 0, l);
for (int i = cnt - l; i > 0; i--) {
data.writeByte((byte) 0);
}
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)
*/
@Override
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());
}
@Override
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);
}
@Override
public String toString() {
return "page [" + getPos() + "] freeList" + (full ? "full" : "");
}
@Override
public boolean canRemove() {
return true;
}
@Override
public boolean canMove() {
return false;
}
}
