org.h2.store.fs.mem.FileMemData Maven / Gradle / Ivy
/*
* Copyright 2004-2021 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.store.fs.mem;
import java.io.IOException;
import java.nio.channels.NonWritableChannelException;
import java.util.Arrays;
import java.util.LinkedHashMap;
import java.util.Map;
import java.util.concurrent.atomic.AtomicReference;
import org.h2.compress.CompressLZF;
import org.h2.util.MathUtils;
/**
* This class contains the data of an in-memory random access file.
* Data compression using the LZF algorithm is supported as well.
*/
class FileMemData {
private static final int CACHE_SIZE = 8;
private static final int BLOCK_SIZE_SHIFT = 10;
private static final int BLOCK_SIZE = 1 << BLOCK_SIZE_SHIFT;
private static final int BLOCK_SIZE_MASK = BLOCK_SIZE - 1;
private static final CompressLZF LZF = new CompressLZF();
private static final byte[] BUFFER = new byte[BLOCK_SIZE * 2];
private static final byte[] COMPRESSED_EMPTY_BLOCK;
private static final Cache COMPRESS_LATER =
new Cache<>(CACHE_SIZE);
private String name;
private final int id;
private final boolean compress;
private volatile long length;
private AtomicReference[] data;
private long lastModified;
private boolean isReadOnly;
private boolean isLockedExclusive;
private int sharedLockCount;
static {
byte[] n = new byte[BLOCK_SIZE];
int len = LZF.compress(n, 0, BLOCK_SIZE, BUFFER, 0);
COMPRESSED_EMPTY_BLOCK = Arrays.copyOf(BUFFER, len);
}
@SuppressWarnings("unchecked")
FileMemData(String name, boolean compress) {
this.name = name;
this.id = name.hashCode();
this.compress = compress;
this.data = new AtomicReference[0];
lastModified = System.currentTimeMillis();
}
/**
* Get the page if it exists.
*
* @param page the page id
* @return the byte array, or null
*/
private byte[] getPage(int page) {
AtomicReference[] b = data;
if (page >= b.length) {
return null;
}
return b[page].get();
}
/**
* Set the page data.
*
* @param page the page id
* @param oldData the old data
* @param newData the new data
* @param force whether the data should be overwritten even if the old data
* doesn't match
*/
private void setPage(int page, byte[] oldData, byte[] newData, boolean force) {
AtomicReference[] b = data;
if (page >= b.length) {
return;
}
if (force) {
b[page].set(newData);
} else {
b[page].compareAndSet(oldData, newData);
}
}
int getId() {
return id;
}
/**
* Lock the file in exclusive mode if possible.
*
* @return if locking was successful
*/
synchronized boolean lockExclusive() {
if (sharedLockCount > 0 || isLockedExclusive) {
return false;
}
isLockedExclusive = true;
return true;
}
/**
* Lock the file in shared mode if possible.
*
* @return if locking was successful
*/
synchronized boolean lockShared() {
if (isLockedExclusive) {
return false;
}
sharedLockCount++;
return true;
}
/**
* Unlock the file.
*/
synchronized void unlock() throws IOException {
if (isLockedExclusive) {
isLockedExclusive = false;
} else if (sharedLockCount > 0) {
sharedLockCount--;
} else {
throw new IOException("not locked");
}
}
/**
* This small cache compresses the data if an element leaves the cache.
*/
static class Cache extends LinkedHashMap {
private static final long serialVersionUID = 1L;
private final int size;
Cache(int size) {
super(size, (float) 0.75, true);
this.size = size;
}
@Override
public synchronized V put(K key, V value) {
return super.put(key, value);
}
@Override
protected boolean removeEldestEntry(Map.Entry eldest) {
if (size() < size) {
return false;
}
CompressItem c = (CompressItem) eldest.getKey();
c.file.compress(c.page);
return true;
}
}
/**
* Points to a block of bytes that needs to be compressed.
*/
static class CompressItem {
/**
* The file.
*/
FileMemData file;
/**
* The page to compress.
*/
int page;
@Override
public int hashCode() {
return page ^ file.getId();
}
@Override
public boolean equals(Object o) {
if (o instanceof CompressItem) {
CompressItem c = (CompressItem) o;
return c.page == page && c.file == file;
}
return false;
}
}
private void compressLater(int page) {
CompressItem c = new CompressItem();
c.file = this;
c.page = page;
synchronized (LZF) {
COMPRESS_LATER.put(c, c);
}
}
private byte[] expand(int page) {
byte[] d = getPage(page);
if (d.length == BLOCK_SIZE) {
return d;
}
byte[] out = new byte[BLOCK_SIZE];
if (d != COMPRESSED_EMPTY_BLOCK) {
synchronized (LZF) {
LZF.expand(d, 0, d.length, out, 0, BLOCK_SIZE);
}
}
setPage(page, d, out, false);
return out;
}
/**
* Compress the data in a byte array.
*
* @param page which page to compress
*/
void compress(int page) {
byte[] old = getPage(page);
if (old == null || old.length != BLOCK_SIZE) {
// not yet initialized or already compressed
return;
}
synchronized (LZF) {
int len = LZF.compress(old, 0, BLOCK_SIZE, BUFFER, 0);
if (len <= BLOCK_SIZE) {
byte[] d = Arrays.copyOf(BUFFER, len);
// maybe data was changed in the meantime
setPage(page, old, d, false);
}
}
}
/**
* Update the last modified time.
*
* @param openReadOnly if the file was opened in read-only mode
*/
void touch(boolean openReadOnly) {
if (isReadOnly || openReadOnly) {
throw new NonWritableChannelException();
}
lastModified = System.currentTimeMillis();
}
/**
* Get the file length.
*
* @return the length
*/
long length() {
return length;
}
/**
* Truncate the file.
*
* @param newLength the new length
*/
void truncate(long newLength) {
changeLength(newLength);
long end = MathUtils.roundUpLong(newLength, BLOCK_SIZE);
if (end != newLength) {
int lastPage = (int) (newLength >>> BLOCK_SIZE_SHIFT);
byte[] d = expand(lastPage);
byte[] d2 = Arrays.copyOf(d, d.length);
for (int i = (int) (newLength & BLOCK_SIZE_MASK); i < BLOCK_SIZE; i++) {
d2[i] = 0;
}
setPage(lastPage, d, d2, true);
if (compress) {
compressLater(lastPage);
}
}
}
private void changeLength(long len) {
length = len;
len = MathUtils.roundUpLong(len, BLOCK_SIZE);
int blocks = (int) (len >>> BLOCK_SIZE_SHIFT);
if (blocks != data.length) {
AtomicReference[] n = Arrays.copyOf(data, blocks);
for (int i = data.length; i < blocks; i++) {
n[i] = new AtomicReference<>(COMPRESSED_EMPTY_BLOCK);
}
data = n;
}
}
/**
* Read or write.
*
* @param pos the position
* @param b the byte array
* @param off the offset within the byte array
* @param len the number of bytes
* @param write true for writing
* @return the new position
*/
long readWrite(long pos, byte[] b, int off, int len, boolean write) {
long end = pos + len;
if (end > length) {
if (write) {
changeLength(end);
} else {
len = (int) (length - pos);
}
}
while (len > 0) {
int l = (int) Math.min(len, BLOCK_SIZE - (pos & BLOCK_SIZE_MASK));
int page = (int) (pos >>> BLOCK_SIZE_SHIFT);
byte[] block = expand(page);
int blockOffset = (int) (pos & BLOCK_SIZE_MASK);
if (write) {
byte[] p2 = Arrays.copyOf(block, block.length);
System.arraycopy(b, off, p2, blockOffset, l);
setPage(page, block, p2, true);
} else {
System.arraycopy(block, blockOffset, b, off, l);
}
if (compress) {
compressLater(page);
}
off += l;
pos += l;
len -= l;
}
return pos;
}
/**
* Set the file name.
*
* @param name the name
*/
void setName(String name) {
this.name = name;
}
/**
* Get the file name
*
* @return the name
*/
String getName() {
return name;
}
/**
* Get the last modified time.
*
* @return the time
*/
long getLastModified() {
return lastModified;
}
/**
* Check whether writing is allowed.
*
* @return true if it is
*/
boolean canWrite() {
return !isReadOnly;
}
/**
* Set the read-only flag.
*
* @return true
*/
boolean setReadOnly() {
isReadOnly = true;
return true;
}
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