org.h2.store.fs.niomem.FileNioMemData 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.niomem;
import java.nio.ByteBuffer;
import java.nio.channels.NonWritableChannelException;
import java.util.LinkedHashMap;
import java.util.Map;
import java.util.concurrent.atomic.AtomicReference;
import java.util.concurrent.locks.ReentrantReadWriteLock;
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 FileNioMemData {
private static final int CACHE_MIN_SIZE = 8;
private static final int BLOCK_SIZE_SHIFT = 16;
private static final int BLOCK_SIZE = 1 << BLOCK_SIZE_SHIFT;
private static final int BLOCK_SIZE_MASK = BLOCK_SIZE - 1;
private static final ByteBuffer COMPRESSED_EMPTY_BLOCK;
private static final ThreadLocal LZF_THREAD_LOCAL = ThreadLocal.withInitial(CompressLZF::new);
/** the output buffer when compressing */
private static final ThreadLocal COMPRESS_OUT_BUF_THREAD_LOCAL = ThreadLocal
.withInitial(() -> new byte[BLOCK_SIZE * 2]);
/**
* The hash code of the name.
*/
final int nameHashCode;
private final CompressLaterCache compressLaterCache =
new CompressLaterCache<>(CACHE_MIN_SIZE);
private String name;
private final boolean compress;
private final float compressLaterCachePercent;
private volatile long length;
private AtomicReference[] buffers;
private long lastModified;
private boolean isReadOnly;
private boolean isLockedExclusive;
private int sharedLockCount;
private final ReentrantReadWriteLock rwLock = new ReentrantReadWriteLock();
static {
final byte[] n = new byte[BLOCK_SIZE];
final byte[] output = new byte[BLOCK_SIZE * 2];
int len = new CompressLZF().compress(n, 0, BLOCK_SIZE, output, 0);
COMPRESSED_EMPTY_BLOCK = ByteBuffer.allocateDirect(len);
COMPRESSED_EMPTY_BLOCK.put(output, 0, len);
}
@SuppressWarnings("unchecked")
FileNioMemData(String name, boolean compress, float compressLaterCachePercent) {
this.name = name;
this.nameHashCode = name.hashCode();
this.compress = compress;
this.compressLaterCachePercent = compressLaterCachePercent;
buffers = new AtomicReference[0];
lastModified = System.currentTimeMillis();
}
/**
* 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() {
if (isLockedExclusive) {
isLockedExclusive = false;
} else {
sharedLockCount = Math.max(0, sharedLockCount - 1);
}
}
/**
* This small cache compresses the data if an element leaves the cache.
*/
static class CompressLaterCache extends LinkedHashMap {
private static final long serialVersionUID = 1L;
private int size;
CompressLaterCache(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.data.compressPage(c.page);
return true;
}
public void setCacheSize(int size) {
this.size = size;
}
}
/**
* Represents a compressed item.
*/
static class CompressItem {
/**
* The file data.
*/
public final FileNioMemData data;
/**
* The page to compress.
*/
public final int page;
public CompressItem(FileNioMemData data, int page) {
this.data = data;
this.page = page;
}
@Override
public int hashCode() {
return page ^ data.nameHashCode;
}
@Override
public boolean equals(Object o) {
if (o instanceof CompressItem) {
CompressItem c = (CompressItem) o;
return c.data == data && c.page == page;
}
return false;
}
}
private void addToCompressLaterCache(int page) {
CompressItem c = new CompressItem(this, page);
compressLaterCache.put(c, c);
}
private ByteBuffer expandPage(int page) {
final ByteBuffer d = buffers[page].get();
if (d.capacity() == BLOCK_SIZE) {
// already expanded, or not compressed
return d;
}
synchronized (d) {
if (d.capacity() == BLOCK_SIZE) {
return d;
}
ByteBuffer out = ByteBuffer.allocateDirect(BLOCK_SIZE);
if (d != COMPRESSED_EMPTY_BLOCK) {
d.position(0);
CompressLZF.expand(d, out);
}
buffers[page].compareAndSet(d, out);
return out;
}
}
/**
* Compress the data in a byte array.
*
* @param page which page to compress
*/
void compressPage(int page) {
final ByteBuffer d = buffers[page].get();
synchronized (d) {
if (d.capacity() != BLOCK_SIZE) {
// already compressed
return;
}
final byte[] compressOutputBuffer = COMPRESS_OUT_BUF_THREAD_LOCAL.get();
int len = LZF_THREAD_LOCAL.get().compress(d, 0, compressOutputBuffer, 0);
ByteBuffer out = ByteBuffer.allocateDirect(len);
out.put(compressOutputBuffer, 0, len);
buffers[page].compareAndSet(d, out);
}
}
/**
* 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) {
rwLock.writeLock().lock();
try {
changeLength(newLength);
long end = MathUtils.roundUpLong(newLength, BLOCK_SIZE);
if (end != newLength) {
int lastPage = (int) (newLength >>> BLOCK_SIZE_SHIFT);
ByteBuffer d = expandPage(lastPage);
for (int i = (int) (newLength & BLOCK_SIZE_MASK); i < BLOCK_SIZE; i++) {
d.put(i, (byte) 0);
}
if (compress) {
addToCompressLaterCache(lastPage);
}
}
} finally {
rwLock.writeLock().unlock();
}
}
@SuppressWarnings("unchecked")
private void changeLength(long len) {
length = len;
len = MathUtils.roundUpLong(len, BLOCK_SIZE);
int blocks = (int) (len >>> BLOCK_SIZE_SHIFT);
if (blocks != buffers.length) {
final AtomicReference[] newBuffers = new AtomicReference[blocks];
System.arraycopy(buffers, 0, newBuffers, 0,
Math.min(buffers.length, newBuffers.length));
for (int i = buffers.length; i < blocks; i++) {
newBuffers[i] = new AtomicReference<>(COMPRESSED_EMPTY_BLOCK);
}
buffers = newBuffers;
}
compressLaterCache.setCacheSize(Math.max(CACHE_MIN_SIZE, (int) (blocks *
compressLaterCachePercent / 100)));
}
/**
* 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, ByteBuffer b, int off, int len, boolean write) {
final java.util.concurrent.locks.Lock lock = write ? rwLock.writeLock()
: rwLock.readLock();
lock.lock();
try {
long end = pos + len;
if (end > length) {
if (write) {
changeLength(end);
} else {
len = (int) (length - pos);
}
}
while (len > 0) {
final int l = (int) Math.min(len, BLOCK_SIZE - (pos & BLOCK_SIZE_MASK));
final int page = (int) (pos >>> BLOCK_SIZE_SHIFT);
final ByteBuffer block = expandPage(page);
int blockOffset = (int) (pos & BLOCK_SIZE_MASK);
if (write) {
final ByteBuffer srcTmp = b.slice();
final ByteBuffer dstTmp = block.duplicate();
srcTmp.position(off);
srcTmp.limit(off + l);
dstTmp.position(blockOffset);
dstTmp.put(srcTmp);
} else {
// duplicate, so this can be done concurrently
final ByteBuffer tmp = block.duplicate();
tmp.position(blockOffset);
tmp.limit(l + blockOffset);
int oldPosition = b.position();
b.position(off);
b.put(tmp);
// restore old position
b.position(oldPosition);
}
if (compress) {
addToCompressLaterCache(page);
}
off += l;
pos += l;
len -= l;
}
return pos;
} finally {
lock.unlock();
}
}
/**
* 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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