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/*
* Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
* or more contributor license agreements. Licensed under the Elastic License
* 2.0 and the Server Side Public License, v 1; you may not use this file except
* in compliance with, at your election, the Elastic License 2.0 or the Server
* Side Public License, v 1.
*/
package org.elasticsearch.common.util;
import com.carrotsearch.hppc.BitMixer;
import org.apache.lucene.util.BytesRef;
import org.elasticsearch.core.Releasable;
import org.elasticsearch.core.Releasables;
/**
* Specialized hash table implementation similar to Lucene's BytesRefHash that maps
* BytesRef values to ids. Collisions are resolved with open addressing and linear
* probing, growth is smooth thanks to {@link BigArrays}, hashes are cached for faster
* re-hashing and capacity is always a multiple of 2 for faster identification of buckets.
* This class is not thread-safe.
*/
public final class BytesRefHash extends AbstractHash {
private LongArray startOffsets;
private ByteArray bytes;
private IntArray hashes; // we cache hashes for faster re-hashing
private final BytesRef spare;
// Constructor with configurable capacity and default maximum load factor.
public BytesRefHash(long capacity, BigArrays bigArrays) {
this(capacity, DEFAULT_MAX_LOAD_FACTOR, bigArrays);
}
// Constructor with configurable capacity and load factor.
public BytesRefHash(long capacity, float maxLoadFactor, BigArrays bigArrays) {
super(capacity, maxLoadFactor, bigArrays);
boolean success = false;
try {
// `super` allocates a big array so we have to `close` if we fail here or we'll leak it.
startOffsets = bigArrays.newLongArray(capacity + 1, false);
startOffsets.set(0, 0);
bytes = bigArrays.newByteArray(capacity * 3, false);
hashes = bigArrays.newIntArray(capacity, false);
success = true;
} finally {
if (false == success) {
close();
}
}
spare = new BytesRef();
}
// BytesRef has a weak hashCode function so we try to improve it by rehashing using Murmur3
// Feel free to remove rehashing if BytesRef gets a better hash function
private static int rehash(int hash) {
return BitMixer.mix32(hash);
}
/**
* Return the key at 0 <= index <= capacity(). The result is undefined if the slot is unused.
* Beware that the content of the {@link BytesRef} may become invalid as soon as {@link #close()} is called
*/
public BytesRef get(long id, BytesRef dest) {
final long startOffset = startOffsets.get(id);
final int length = (int) (startOffsets.get(id + 1) - startOffset);
bytes.get(startOffset, length, dest);
return dest;
}
/**
* Get the id associated with key
*/
public long find(BytesRef key, int code) {
final long slot = slot(rehash(code), mask);
for (long index = slot;; index = nextSlot(index, mask)) {
final long id = id(index);
if (id == -1L || key.bytesEquals(get(id, spare))) {
return id;
}
}
}
/** Sugar for {@link #find(BytesRef, int) find(key, key.hashCode()} */
public long find(BytesRef key) {
return find(key, key.hashCode());
}
private long set(BytesRef key, int code, long id) {
assert rehash(key.hashCode()) == code;
assert size < maxSize;
final long slot = slot(code, mask);
for (long index = slot;; index = nextSlot(index, mask)) {
final long curId = id(index);
if (curId == -1) { // means unset
id(index, id);
append(id, key, code);
++size;
return id;
} else if (key.bytesEquals(get(curId, spare))) {
return -1 - curId;
}
}
}
private void append(long id, BytesRef key, int code) {
assert size == id;
final long startOffset = startOffsets.get(size);
bytes = bigArrays.grow(bytes, startOffset + key.length);
bytes.set(startOffset, key.bytes, key.offset, key.length);
startOffsets = bigArrays.grow(startOffsets, size + 2);
startOffsets.set(size + 1, startOffset + key.length);
hashes = bigArrays.grow(hashes, id + 1);
hashes.set(id, code);
}
private boolean assertConsistent(long id, int code) {
get(id, spare);
return rehash(spare.hashCode()) == code;
}
private void reset(int code, long id) {
assert assertConsistent(id, code);
final long slot = slot(code, mask);
for (long index = slot;; index = nextSlot(index, mask)) {
final long curId = id(index);
if (curId == -1) { // means unset
id(index, id);
break;
}
}
}
/**
* Try to add key. Return its newly allocated id if it wasn't in the hash table yet, or -1-id
* if it was already present in the hash table.
*/
public long add(BytesRef key, int code) {
if (size >= maxSize) {
assert size == maxSize;
grow();
}
assert size < maxSize;
return set(key, rehash(code), size);
}
/** Sugar to {@link #add(BytesRef, int) add(key, key.hashCode()}. */
public long add(BytesRef key) {
return add(key, key.hashCode());
}
@Override
protected void removeAndAdd(long index) {
final long id = id(index, -1);
assert id >= 0;
final int code = hashes.get(id);
reset(code, id);
}
@Override
public void close() {
try (Releasable releasable = Releasables.wrap(bytes, hashes, startOffsets)) {
super.close();
}
}
}