org.elasticsearch.common.collect.CopyOnWriteHashMap Maven / Gradle / Ivy
Go to download
Show more of this group Show more artifacts with this name
Show all versions of elasticsearch Show documentation
Show all versions of elasticsearch Show documentation
Elasticsearch subproject :server
/*
* Licensed to Elasticsearch under one or more contributor
* license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright
* ownership. Elasticsearch licenses this file to you under
* the Apache License, Version 2.0 (the "License"); you may
* not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing,
* software distributed under the License is distributed on an
* "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
* KIND, either express or implied. See the License for the
* specific language governing permissions and limitations
* under the License.
*/
package org.elasticsearch.common.collect;
import org.apache.lucene.util.mutable.MutableValueInt;
import java.lang.reflect.Array;
import java.util.AbstractMap;
import java.util.AbstractSet;
import java.util.ArrayDeque;
import java.util.Arrays;
import java.util.Collection;
import java.util.Deque;
import java.util.Iterator;
import java.util.Map;
import java.util.NoSuchElementException;
import java.util.Set;
import java.util.stream.Stream;
/**
* An immutable map whose writes result in a new copy of the map to be created.
*
* This is essentially a hash array mapped trie: inner nodes use a bitmap in
* order to map hashes to slots by counting ones. In case of a collision (two
* values having the same 32-bits hash), a leaf node is created which stores
* and searches for values sequentially.
*
* Reads and writes both perform in logarithmic time. Null keys and values are
* not supported.
*
* This structure might need to perform several object creations per write so
* it is better suited for work-loads that are not too write-intensive.
*
* @see the wikipedia page
*/
public final class CopyOnWriteHashMap extends AbstractMap {
private static final int TOTAL_HASH_BITS = 32;
private static final Object[] EMPTY_ARRAY = new Object[0];
private static final int HASH_BITS = 6;
private static final int HASH_MASK = 0x3F;
/**
* Return a copy of the provided map.
*/
public static CopyOnWriteHashMap copyOf(Map map) {
if (map instanceof CopyOnWriteHashMap) {
// no need to copy in that case
@SuppressWarnings("unchecked")
final CopyOnWriteHashMap cowMap = (CopyOnWriteHashMap) map;
return cowMap;
} else {
return new CopyOnWriteHashMap().copyAndPutAll(map);
}
}
/**
* Abstraction of a node, implemented by both inner and leaf nodes.
*/
private abstract static class Node {
/**
* Recursively get the key with the given hash.
*/
abstract V get(Object key, int hash);
/**
* Recursively add a new entry to this node. hashBits is
* the number of bits that are still set in the hash. When this value
* reaches a number that is less than or equal to {@code 0}, a leaf
* node needs to be created since it means that a collision occurred
* on the 32 bits of the hash.
*/
abstract Node put(K key, int hash, int hashBits, V value, MutableValueInt newValue);
/**
* Recursively remove an entry from this node.
*/
abstract Node remove(Object key, int hash);
/**
* For the current node only, append entries that are stored on this
* node to entries and sub nodes to nodes.
*/
abstract void visit(Deque> entries, Deque> nodes);
/**
* Whether this node stores nothing under it.
*/
abstract boolean isEmpty();
}
/**
* A leaf of the tree where all hashes are equal. Values are added and retrieved in linear time.
*/
private static class Leaf extends Node {
private final K[] keys;
private final V[] values;
Leaf(K[] keys, V[] values) {
this.keys = keys;
this.values = values;
}
@SuppressWarnings("unchecked")
Leaf() {
this((K[]) EMPTY_ARRAY, (V[]) EMPTY_ARRAY);
}
@Override
boolean isEmpty() {
return keys.length == 0;
}
@Override
void visit(Deque> entries, Deque> nodes) {
for (int i = 0; i < keys.length; ++i) {
entries.add(new AbstractMap.SimpleImmutableEntry<>(keys[i], values[i]));
}
}
@Override
V get(Object key, int hash) {
for (int i = 0; i < keys.length; i++) {
if (key.equals(keys[i])) {
return values[i];
}
}
return null;
}
private static T[] replace(T[] array, int index, T value) {
final T[] copy = Arrays.copyOf(array, array.length);
copy[index] = value;
return copy;
}
@Override
Leaf put(K key, int hash, int hashBits, V value, MutableValueInt newValue) {
assert hashBits <= 0 : hashBits;
int slot = -1;
for (int i = 0; i < keys.length; i++) {
if (key.equals(keys[i])) {
slot = i;
break;
}
}
final K[] keys2;
final V[] values2;
if (slot < 0) {
keys2 = appendElement(keys, key);
values2 = appendElement(values, value);
newValue.value = 1;
} else {
keys2 = replace(keys, slot, key);
values2 = replace(values, slot, value);
}
return new Leaf<>(keys2, values2);
}
@Override
Leaf remove(Object key, int hash) {
int slot = -1;
for (int i = 0; i < keys.length; i++) {
if (key.equals(keys[i])) {
slot = i;
break;
}
}
if (slot < 0) {
return this;
}
final K[] keys2 = removeArrayElement(keys, slot);
final V[] values2 = removeArrayElement(values, slot);
return new Leaf<>(keys2, values2);
}
}
private static T[] removeArrayElement(T[] array, int index) {
final Object result = Array.newInstance(array.getClass().getComponentType(), array.length - 1);
System.arraycopy(array, 0, result, 0, index);
if (index < array.length - 1) {
System.arraycopy(array, index + 1, result, index, array.length - index - 1);
}
return (T[]) result;
}
public static T[] appendElement(final T[] array, final T element) {
final T[] newArray = Arrays.copyOf(array, array.length + 1);
newArray[newArray.length - 1] = element;
return newArray;
}
public static T[] insertElement(final T[] array, final T element, final int index) {
final T[] result = Arrays.copyOf(array, array.length + 1);
System.arraycopy(array, 0, result, 0, index);
result[index] = element;
if (index < array.length) {
System.arraycopy(array, index, result, index + 1, array.length - index);
}
return result;
}
/**
* An inner node in this trie. Inner nodes store up to 64 key-value pairs
* and use a bitmap in order to associate hashes to them. For example, if
* an inner node contains 5 values, then 5 bits will be set in the bitmap
* and the ordinal of the bit set in this bit map will be the slot number.
*
* As a consequence, the number of slots in an inner node is equal to the
* number of one bits in the bitmap.
*/
private static class InnerNode extends Node {
private final long mask; // the bitmap
private final K[] keys;
final Object[] subNodes; // subNodes[slot] is either a value or a sub node in case of a hash collision
InnerNode(long mask, K[] keys, Object[] subNodes) {
this.mask = mask;
this.keys = keys;
this.subNodes = subNodes;
assert consistent();
}
// only used in assert
private boolean consistent() {
assert Long.bitCount(mask) == keys.length;
assert Long.bitCount(mask) == subNodes.length;
for (int i = 0; i < keys.length; ++i) {
if (subNodes[i] instanceof Node) {
assert keys[i] == null;
} else {
assert keys[i] != null;
}
}
return true;
}
@Override
boolean isEmpty() {
return mask == 0;
}
@SuppressWarnings("unchecked")
InnerNode() {
this(0, (K[]) EMPTY_ARRAY, EMPTY_ARRAY);
}
@Override
void visit(Deque> entries, Deque> nodes) {
for (int i = 0; i < keys.length; ++i) {
final Object sub = subNodes[i];
if (sub instanceof Node) {
@SuppressWarnings("unchecked")
final Node subNode = (Node) sub;
assert keys[i] == null;
nodes.add(subNode);
} else {
@SuppressWarnings("unchecked")
final V value = (V) sub;
entries.add(new AbstractMap.SimpleImmutableEntry<>(keys[i], value));
}
}
}
/**
* For a given hash on 6 bits, its value is set if the bitmap has a one
* at the corresponding index.
*/
private boolean exists(int hash6) {
return (mask & (1L << hash6)) != 0;
}
/**
* For a given hash on 6 bits, the slot number is the number of one
* bits on the right of the hash6-th bit.
*/
private int slot(int hash6) {
return Long.bitCount(mask & ((1L << hash6) - 1));
}
@Override
V get(Object key, int hash) {
final int hash6 = hash & HASH_MASK;
if (!exists(hash6)) {
return null;
}
final int slot = slot(hash6);
final Object sub = subNodes[slot];
assert sub != null;
if (sub instanceof Node) {
assert keys[slot] == null; // keys don't make sense on inner nodes
@SuppressWarnings("unchecked")
final Node subNode = (Node) sub;
return subNode.get(key, hash >>> HASH_BITS);
} else {
if (keys[slot].equals(key)) {
@SuppressWarnings("unchecked")
final V v = (V) sub;
return v;
} else {
// we have an entry for this hash, but the value is different
return null;
}
}
}
private Node newSubNode(int hashBits) {
if (hashBits <= 0) {
return new Leaf();
} else {
return new InnerNode();
}
}
private InnerNode putExisting(K key, int hash, int hashBits, int slot, V value, MutableValueInt newValue) {
final K[] keys2 = Arrays.copyOf(keys, keys.length);
final Object[] subNodes2 = Arrays.copyOf(subNodes, subNodes.length);
final Object previousValue = subNodes2[slot];
if (previousValue instanceof Node) {
// insert recursively
assert keys[slot] == null;
subNodes2[slot] = ((Node) previousValue).put(key, hash, hashBits, value, newValue);
} else if (keys[slot].equals(key)) {
// replace the existing entry
subNodes2[slot] = value;
} else {
// hash collision
final K previousKey = keys[slot];
final int previousHash = previousKey.hashCode() >>> (TOTAL_HASH_BITS - hashBits);
Node subNode = newSubNode(hashBits);
subNode = subNode.put(previousKey, previousHash, hashBits, (V) previousValue, newValue);
subNode = subNode.put(key, hash, hashBits, value, newValue);
keys2[slot] = null;
subNodes2[slot] = subNode;
}
return new InnerNode<>(mask, keys2, subNodes2);
}
private InnerNode putNew(K key, int hash6, int slot, V value) {
final long mask2 = mask | (1L << hash6);
final K[] keys2 = insertElement(keys, key, slot);
final Object[] subNodes2 = insertElement(subNodes, value, slot);
return new InnerNode<>(mask2, keys2, subNodes2);
}
@Override
InnerNode put(K key, int hash, int hashBits, V value, MutableValueInt newValue) {
final int hash6 = hash & HASH_MASK;
final int slot = slot(hash6);
if (exists(hash6)) {
hash >>>= HASH_BITS;
hashBits -= HASH_BITS;
return putExisting(key, hash, hashBits, slot, value, newValue);
} else {
newValue.value = 1;
return putNew(key, hash6, slot, value);
}
}
private InnerNode removeSlot(int hash6, int slot) {
final long mask2 = mask & ~(1L << hash6);
final K[] keys2 = removeArrayElement(keys, slot);
final Object[] subNodes2 = removeArrayElement(subNodes, slot);
return new InnerNode<>(mask2, keys2, subNodes2);
}
@Override
InnerNode remove(Object key, int hash) {
final int hash6 = hash & HASH_MASK;
if (!exists(hash6)) {
return this;
}
final int slot = slot(hash6);
final Object previousValue = subNodes[slot];
if (previousValue instanceof Node) {
@SuppressWarnings("unchecked")
final Node subNode = (Node) previousValue;
final Node removed = subNode.remove(key, hash >>> HASH_BITS);
if (removed == subNode) {
// not in sub-nodes
return this;
}
if (removed.isEmpty()) {
return removeSlot(hash6, slot);
}
final K[] keys2 = Arrays.copyOf(keys, keys.length);
final Object[] subNodes2 = Arrays.copyOf(subNodes, subNodes.length);
subNodes2[slot] = removed;
return new InnerNode<>(mask, keys2, subNodes2);
} else if (keys[slot].equals(key)) {
// remove entry
return removeSlot(hash6, slot);
} else {
// hash collision, nothing to remove
return this;
}
}
}
private static class EntryIterator implements Iterator> {
private final Deque> entries;
private final Deque> nodes;
EntryIterator(Node node) {
entries = new ArrayDeque<>();
nodes = new ArrayDeque<>();
node.visit(entries, nodes);
}
@Override
public boolean hasNext() {
return !entries.isEmpty() || !nodes.isEmpty();
}
@Override
public Map.Entry next() {
while (entries.isEmpty()) {
if (nodes.isEmpty()) {
throw new NoSuchElementException();
}
final Node nextNode = nodes.pop();
nextNode.visit(entries, nodes);
}
return entries.pop();
}
@Override
public final void remove() {
throw new UnsupportedOperationException();
}
}
private final InnerNode root;
private final int size;
/**
* Create a new empty map.
*/
public CopyOnWriteHashMap() {
this(new InnerNode(), 0);
}
private CopyOnWriteHashMap(InnerNode root, int size) {
this.root = root;
this.size = size;
}
@Override
public boolean containsKey(Object key) {
// works fine since null values are not supported
return get(key) != null;
}
@Override
public V get(Object key) {
if (key == null) {
throw new IllegalArgumentException("null keys are not supported");
}
final int hash = key.hashCode();
return root.get(key, hash);
}
@Override
public int size() {
assert size != 0 || root.isEmpty();
return size;
}
/**
* Associate key with value and return a new copy
* of the hash table. The current hash table is not modified.
*/
public CopyOnWriteHashMap copyAndPut(K key, V value) {
if (key == null) {
throw new IllegalArgumentException("null keys are not supported");
}
if (value == null) {
throw new IllegalArgumentException("null values are not supported");
}
final int hash = key.hashCode();
final MutableValueInt newValue = new MutableValueInt();
final InnerNode newRoot = root.put(key, hash, TOTAL_HASH_BITS, value, newValue);
final int newSize = size + newValue.value;
return new CopyOnWriteHashMap<>(newRoot, newSize);
}
/**
* Same as {@link #copyAndPut(Object, Object)} but for an arbitrary number of entries.
*/
public CopyOnWriteHashMap copyAndPutAll(Map other) {
return copyAndPutAll(other.entrySet());
}
public CopyOnWriteHashMap copyAndPutAll(Iterable> entries) {
CopyOnWriteHashMap result = this;
for (Entry entry : entries) {
result = result.copyAndPut(entry.getKey(), entry.getValue());
}
return result;
}
public CopyOnWriteHashMap copyAndPutAll(Stream> entries) {
return copyAndPutAll(entries::iterator);
}
/**
* Remove the given key from this map. The current hash table is not modified.
*/
public CopyOnWriteHashMap copyAndRemove(Object key) {
if (key == null) {
throw new IllegalArgumentException("null keys are not supported");
}
final int hash = key.hashCode();
final InnerNode newRoot = root.remove(key, hash);
if (root == newRoot) {
return this;
} else {
return new CopyOnWriteHashMap<>(newRoot, size - 1);
}
}
/**
* Same as {@link #copyAndRemove(Object)} but for an arbitrary number of entries.
*/
public CopyOnWriteHashMap copyAndRemoveAll(Collection keys) {
CopyOnWriteHashMap result = this;
for (Object key : keys) {
result = result.copyAndRemove(key);
}
return result;
}
@Override
public Set> entrySet() {
return new AbstractSet>() {
@Override
public Iterator> iterator() {
return new EntryIterator<>(root);
}
@Override
public boolean contains(Object o) {
if (o == null || !(o instanceof Map.Entry)) {
return false;
}
Map.Entry entry = (java.util.Map.Entry) o;
return entry.getValue().equals(CopyOnWriteHashMap.this.get(entry.getKey()));
}
@Override
public int size() {
return CopyOnWriteHashMap.this.size();
}
};
}
}