com.google.common.collect.CompactHashMap Maven / Gradle / Ivy
/*
* Copyright (C) 2012 The Guava Authors
*
* Licensed 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 com.google.common.collect;
import static com.google.common.collect.CollectPreconditions.checkRemove;
import static com.google.common.collect.Hashing.smearedHash;
import com.google.common.annotations.GwtIncompatible;
import com.google.common.annotations.VisibleForTesting;
import com.google.common.base.Objects;
import com.google.common.base.Preconditions;
import com.google.errorprone.annotations.CanIgnoreReturnValue;
import com.google.j2objc.annotations.WeakOuter;
import java.io.IOException;
import java.io.InvalidObjectException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.Serializable;
import java.util.AbstractCollection;
import java.util.AbstractMap;
import java.util.AbstractSet;
import java.util.Arrays;
import java.util.Collection;
import java.util.ConcurrentModificationException;
import java.util.Iterator;
import java.util.NoSuchElementException;
import java.util.Set;
import org.checkerframework.checker.nullness.compatqual.MonotonicNonNullDecl;
import org.checkerframework.checker.nullness.compatqual.NullableDecl;
/**
* CompactHashMap is an implementation of a Map. All optional operations (put and remove) are
* supported. Null keys and values are supported.
*
* {@code containsKey(k)}, {@code put(k, v)} and {@code remove(k)} are all (expected and
* amortized) constant time operations. Expected in the hashtable sense (depends on the hash
* function doing a good job of distributing the elements to the buckets to a distribution not far
* from uniform), and amortized since some operations can trigger a hash table resize.
*
*
Unlike {@code java.util.HashMap}, iteration is only proportional to the actual {@code size()},
* which is optimal, and not the size of the internal hashtable, which could be much larger
* than {@code size()}. Furthermore, this structure places significantly reduced load on the garbage
* collector by only using a constant number of internal objects.
*
*
If there are no removals, then iteration order for the {@link #entrySet}, {@link #keySet}, and
* {@link #values} views is the same as insertion order. Any removal invalidates any ordering
* guarantees.
*
*
This class should not be assumed to be universally superior to {@code java.util.HashMap}.
* Generally speaking, this class reduces object allocation and memory consumption at the price of
* moderately increased constant factors of CPU. Only use this class when there is a specific reason
* to prioritize memory over CPU.
*
* @author Louis Wasserman
*/
@GwtIncompatible // not worth using in GWT for now
class CompactHashMap extends AbstractMap implements Serializable {
/*
* TODO: Make this a drop-in replacement for j.u. versions, actually drop them in, and test the
* world. Figure out what sort of space-time tradeoff we're actually going to get here with the
* *Map variants. Followon optimizations, such as using 16-bit indices for small collections, will
* take more work to implement. This class is particularly hard to benchmark, because the benefit
* is not only in less allocation, but also having the GC do less work to scan the heap because of
* fewer references, which is particularly hard to quantify.
*/
/** Creates an empty {@code CompactHashMap} instance. */
public static CompactHashMap create() {
return new CompactHashMap<>();
}
/**
* Creates a {@code CompactHashMap} instance, with a high enough "initial capacity" that it
* should hold {@code expectedSize} elements without growth.
*
* @param expectedSize the number of elements you expect to add to the returned set
* @return a new, empty {@code CompactHashMap} with enough capacity to hold {@code expectedSize}
* elements without resizing
* @throws IllegalArgumentException if {@code expectedSize} is negative
*/
public static CompactHashMap createWithExpectedSize(int expectedSize) {
return new CompactHashMap<>(expectedSize);
}
private static final float LOAD_FACTOR = 1.0f;
/** Bitmask that selects the low 32 bits. */
private static final long NEXT_MASK = (1L << 32) - 1;
/** Bitmask that selects the high 32 bits. */
private static final long HASH_MASK = ~NEXT_MASK;
// TODO(user): decide default size
static final int DEFAULT_SIZE = 3;
// used to indicate blank table entries
static final int UNSET = -1;
/**
* The hashtable. Its values are indexes to the keys, values, and entries arrays.
*
* Currently, the UNSET value means "null pointer", and any non negative value x is the actual
* index.
*
*
Its size must be a power of two.
*/
@MonotonicNonNullDecl private transient int[] table;
/**
* Contains the logical entries, in the range of [0, size()). The high 32 bits of each long is the
* smeared hash of the element, whereas the low 32 bits is the "next" pointer (pointing to the
* next entry in the bucket chain). The pointers in [size(), entries.length) are all "null"
* (UNSET).
*/
@VisibleForTesting @MonotonicNonNullDecl transient long[] entries;
/**
* The keys of the entries in the map, in the range of [0, size()). The keys in [size(),
* keys.length) are all {@code null}.
*/
@VisibleForTesting @MonotonicNonNullDecl transient Object[] keys;
/**
* The values of the entries in the map, in the range of [0, size()). The values in [size(),
* values.length) are all {@code null}.
*/
@VisibleForTesting @MonotonicNonNullDecl transient Object[] values;
/**
* Keeps track of modifications of this set, to make it possible to throw
* ConcurrentModificationException in the iterator. Note that we choose not to make this volatile,
* so we do less of a "best effort" to track such errors, for better performance.
*/
transient int modCount;
/** The number of elements contained in the set. */
private transient int size;
/** Constructs a new empty instance of {@code CompactHashMap}. */
CompactHashMap() {
init(DEFAULT_SIZE);
}
/**
* Constructs a new instance of {@code CompactHashMap} with the specified capacity.
*
* @param expectedSize the initial capacity of this {@code CompactHashMap}.
*/
CompactHashMap(int expectedSize) {
init(expectedSize);
}
/** Pseudoconstructor for serialization support. */
void init(int expectedSize) {
Preconditions.checkArgument(expectedSize >= 0, "Expected size must be non-negative");
this.modCount = Math.max(1, expectedSize); // Save expectedSize for use in allocArrays()
}
/** Returns whether arrays need to be allocated. */
boolean needsAllocArrays() {
return table == null;
}
/** Handle lazy allocation of arrays. */
void allocArrays() {
Preconditions.checkState(needsAllocArrays(), "Arrays already allocated");
int expectedSize = modCount;
int buckets = Hashing.closedTableSize(expectedSize, LOAD_FACTOR);
this.table = newTable(buckets);
this.entries = newEntries(expectedSize);
this.keys = new Object[expectedSize];
this.values = new Object[expectedSize];
}
private static int[] newTable(int size) {
int[] array = new int[size];
Arrays.fill(array, UNSET);
return array;
}
private static long[] newEntries(int size) {
long[] array = new long[size];
Arrays.fill(array, UNSET);
return array;
}
private int hashTableMask() {
return table.length - 1;
}
private static int getHash(long entry) {
return (int) (entry >>> 32);
}
/** Returns the index, or UNSET if the pointer is "null" */
private static int getNext(long entry) {
return (int) entry;
}
/** Returns a new entry value by changing the "next" index of an existing entry */
private static long swapNext(long entry, int newNext) {
return (HASH_MASK & entry) | (NEXT_MASK & newNext);
}
/**
* Mark an access of the specified entry. Used only in {@code CompactLinkedHashMap} for LRU
* ordering.
*/
void accessEntry(int index) {
// no-op by default
}
@CanIgnoreReturnValue
@Override
@NullableDecl
public V put(@NullableDecl K key, @NullableDecl V value) {
if (needsAllocArrays()) {
allocArrays();
}
long[] entries = this.entries;
Object[] keys = this.keys;
Object[] values = this.values;
int hash = smearedHash(key);
int tableIndex = hash & hashTableMask();
int newEntryIndex = this.size; // current size, and pointer to the entry to be appended
int next = table[tableIndex];
if (next == UNSET) { // uninitialized bucket
table[tableIndex] = newEntryIndex;
} else {
int last;
long entry;
do {
last = next;
entry = entries[next];
if (getHash(entry) == hash && Objects.equal(key, keys[next])) {
@SuppressWarnings("unchecked") // known to be a V
@NullableDecl
V oldValue = (V) values[next];
values[next] = value;
accessEntry(next);
return oldValue;
}
next = getNext(entry);
} while (next != UNSET);
entries[last] = swapNext(entry, newEntryIndex);
}
if (newEntryIndex == Integer.MAX_VALUE) {
throw new IllegalStateException("Cannot contain more than Integer.MAX_VALUE elements!");
}
int newSize = newEntryIndex + 1;
resizeMeMaybe(newSize);
insertEntry(newEntryIndex, key, value, hash);
this.size = newSize;
int oldCapacity = table.length;
if (Hashing.needsResizing(newEntryIndex, oldCapacity, LOAD_FACTOR)) {
resizeTable(2 * oldCapacity);
}
modCount++;
return null;
}
/**
* Creates a fresh entry with the specified object at the specified position in the entry arrays.
*/
void insertEntry(int entryIndex, @NullableDecl K key, @NullableDecl V value, int hash) {
this.entries[entryIndex] = ((long) hash << 32) | (NEXT_MASK & UNSET);
this.keys[entryIndex] = key;
this.values[entryIndex] = value;
}
/** Resizes the entries storage if necessary. */
private void resizeMeMaybe(int newSize) {
int entriesSize = entries.length;
if (newSize > entriesSize) {
int newCapacity = entriesSize + Math.max(1, entriesSize >>> 1);
if (newCapacity < 0) {
newCapacity = Integer.MAX_VALUE;
}
if (newCapacity != entriesSize) {
resizeEntries(newCapacity);
}
}
}
/**
* Resizes the internal entries array to the specified capacity, which may be greater or less than
* the current capacity.
*/
void resizeEntries(int newCapacity) {
this.keys = Arrays.copyOf(keys, newCapacity);
this.values = Arrays.copyOf(values, newCapacity);
long[] entries = this.entries;
int oldCapacity = entries.length;
entries = Arrays.copyOf(entries, newCapacity);
if (newCapacity > oldCapacity) {
Arrays.fill(entries, oldCapacity, newCapacity, UNSET);
}
this.entries = entries;
}
private void resizeTable(int newCapacity) { // newCapacity always a power of two
int[] newTable = newTable(newCapacity);
long[] entries = this.entries;
int mask = newTable.length - 1;
for (int i = 0; i < size; i++) {
long oldEntry = entries[i];
int hash = getHash(oldEntry);
int tableIndex = hash & mask;
int next = newTable[tableIndex];
newTable[tableIndex] = i;
entries[i] = ((long) hash << 32) | (NEXT_MASK & next);
}
this.table = newTable;
}
private int indexOf(@NullableDecl Object key) {
if (needsAllocArrays()) {
return -1;
}
int hash = smearedHash(key);
int next = table[hash & hashTableMask()];
while (next != UNSET) {
long entry = entries[next];
if (getHash(entry) == hash && Objects.equal(key, keys[next])) {
return next;
}
next = getNext(entry);
}
return -1;
}
@Override
public boolean containsKey(@NullableDecl Object key) {
return indexOf(key) != -1;
}
@SuppressWarnings("unchecked") // values only contains Vs
@Override
public V get(@NullableDecl Object key) {
int index = indexOf(key);
accessEntry(index);
return (index == -1) ? null : (V) values[index];
}
@CanIgnoreReturnValue
@Override
@NullableDecl
public V remove(@NullableDecl Object key) {
if (needsAllocArrays()) {
return null;
}
return remove(key, smearedHash(key));
}
@NullableDecl
private V remove(@NullableDecl Object key, int hash) {
int tableIndex = hash & hashTableMask();
int next = table[tableIndex];
if (next == UNSET) { // empty bucket
return null;
}
int last = UNSET;
do {
if (getHash(entries[next]) == hash && Objects.equal(key, keys[next])) {
@SuppressWarnings("unchecked") // values only contains Vs
@NullableDecl
V oldValue = (V) values[next];
if (last == UNSET) {
// we need to update the root link from table[]
table[tableIndex] = getNext(entries[next]);
} else {
// we need to update the link from the chain
entries[last] = swapNext(entries[last], getNext(entries[next]));
}
moveLastEntry(next);
size--;
modCount++;
return oldValue;
}
last = next;
next = getNext(entries[next]);
} while (next != UNSET);
return null;
}
@CanIgnoreReturnValue
private V removeEntry(int entryIndex) {
return remove(keys[entryIndex], getHash(entries[entryIndex]));
}
/**
* Moves the last entry in the entry array into {@code dstIndex}, and nulls out its old position.
*/
void moveLastEntry(int dstIndex) {
int srcIndex = size() - 1;
if (dstIndex < srcIndex) {
// move last entry to deleted spot
keys[dstIndex] = keys[srcIndex];
values[dstIndex] = values[srcIndex];
keys[srcIndex] = null;
values[srcIndex] = null;
// move the last entry to the removed spot, just like we moved the element
long lastEntry = entries[srcIndex];
entries[dstIndex] = lastEntry;
entries[srcIndex] = UNSET;
// also need to update whoever's "next" pointer was pointing to the last entry place
// reusing "tableIndex" and "next"; these variables were no longer needed
int tableIndex = getHash(lastEntry) & hashTableMask();
int lastNext = table[tableIndex];
if (lastNext == srcIndex) {
// we need to update the root pointer
table[tableIndex] = dstIndex;
} else {
// we need to update a pointer in an entry
int previous;
long entry;
do {
previous = lastNext;
lastNext = getNext(entry = entries[lastNext]);
} while (lastNext != srcIndex);
// here, entries[previous] points to the old entry location; update it
entries[previous] = swapNext(entry, dstIndex);
}
} else {
keys[dstIndex] = null;
values[dstIndex] = null;
entries[dstIndex] = UNSET;
}
}
int firstEntryIndex() {
return isEmpty() ? -1 : 0;
}
int getSuccessor(int entryIndex) {
return (entryIndex + 1 < size) ? entryIndex + 1 : -1;
}
/**
* Updates the index an iterator is pointing to after a call to remove: returns the index of the
* entry that should be looked at after a removal on indexRemoved, with indexBeforeRemove as the
* index that *was* the next entry that would be looked at.
*/
int adjustAfterRemove(int indexBeforeRemove, @SuppressWarnings("unused") int indexRemoved) {
return indexBeforeRemove - 1;
}
private abstract class Itr implements Iterator {
int expectedModCount = modCount;
int currentIndex = firstEntryIndex();
int indexToRemove = -1;
@Override
public boolean hasNext() {
return currentIndex >= 0;
}
abstract T getOutput(int entry);
@Override
public T next() {
checkForConcurrentModification();
if (!hasNext()) {
throw new NoSuchElementException();
}
indexToRemove = currentIndex;
T result = getOutput(currentIndex);
currentIndex = getSuccessor(currentIndex);
return result;
}
@Override
public void remove() {
checkForConcurrentModification();
checkRemove(indexToRemove >= 0);
expectedModCount++;
removeEntry(indexToRemove);
currentIndex = adjustAfterRemove(currentIndex, indexToRemove);
indexToRemove = -1;
}
private void checkForConcurrentModification() {
if (modCount != expectedModCount) {
throw new ConcurrentModificationException();
}
}
}
@MonotonicNonNullDecl private transient Set keySetView;
@Override
public Set keySet() {
return (keySetView == null) ? keySetView = createKeySet() : keySetView;
}
Set createKeySet() {
return new KeySetView();
}
@WeakOuter
class KeySetView extends AbstractSet {
@Override
public int size() {
return size;
}
@Override
public boolean contains(Object o) {
return CompactHashMap.this.containsKey(o);
}
@Override
public boolean remove(@NullableDecl Object o) {
int index = indexOf(o);
if (index == -1) {
return false;
} else {
removeEntry(index);
return true;
}
}
@Override
public Iterator iterator() {
return keySetIterator();
}
@Override
public void clear() {
CompactHashMap.this.clear();
}
}
Iterator keySetIterator() {
return new Itr() {
@SuppressWarnings("unchecked") // keys only contains Ks
@Override
K getOutput(int entry) {
return (K) keys[entry];
}
};
}
@MonotonicNonNullDecl private transient Set> entrySetView;
@Override
public Set> entrySet() {
return (entrySetView == null) ? entrySetView = createEntrySet() : entrySetView;
}
Set> createEntrySet() {
return new EntrySetView();
}
@WeakOuter
class EntrySetView extends AbstractSet> {
@Override
public int size() {
return size;
}
@Override
public void clear() {
CompactHashMap.this.clear();
}
@Override
public Iterator> iterator() {
return entrySetIterator();
}
@Override
public boolean contains(@NullableDecl Object o) {
if (o instanceof Entry) {
Entry entry = (Entry) o;
int index = indexOf(entry.getKey());
return index != -1 && Objects.equal(values[index], entry.getValue());
}
return false;
}
@Override
public boolean remove(@NullableDecl Object o) {
if (o instanceof Entry) {
Entry entry = (Entry) o;
int index = indexOf(entry.getKey());
if (index != -1 && Objects.equal(values[index], entry.getValue())) {
removeEntry(index);
return true;
}
}
return false;
}
}
Iterator> entrySetIterator() {
return new Itr>() {
@Override
Entry getOutput(int entry) {
return new MapEntry(entry);
}
};
}
final class MapEntry extends AbstractMapEntry {
@NullableDecl private final K key;
private int lastKnownIndex;
@SuppressWarnings("unchecked") // keys only contains Ks
MapEntry(int index) {
this.key = (K) keys[index];
this.lastKnownIndex = index;
}
@Override
public K getKey() {
return key;
}
private void updateLastKnownIndex() {
if (lastKnownIndex == -1
|| lastKnownIndex >= size()
|| !Objects.equal(key, keys[lastKnownIndex])) {
lastKnownIndex = indexOf(key);
}
}
@SuppressWarnings("unchecked") // values only contains Vs
@Override
public V getValue() {
updateLastKnownIndex();
return (lastKnownIndex == -1) ? null : (V) values[lastKnownIndex];
}
@SuppressWarnings("unchecked") // values only contains Vs
@Override
public V setValue(V value) {
updateLastKnownIndex();
if (lastKnownIndex == -1) {
put(key, value);
return null;
} else {
V old = (V) values[lastKnownIndex];
values[lastKnownIndex] = value;
return old;
}
}
}
@Override
public int size() {
return size;
}
@Override
public boolean isEmpty() {
return size == 0;
}
@Override
public boolean containsValue(@NullableDecl Object value) {
for (int i = 0; i < size; i++) {
if (Objects.equal(value, values[i])) {
return true;
}
}
return false;
}
@MonotonicNonNullDecl private transient Collection valuesView;
@Override
public Collection values() {
return (valuesView == null) ? valuesView = createValues() : valuesView;
}
Collection createValues() {
return new ValuesView();
}
@WeakOuter
class ValuesView extends AbstractCollection {
@Override
public int size() {
return size;
}
@Override
public void clear() {
CompactHashMap.this.clear();
}
@Override
public Iterator iterator() {
return valuesIterator();
}
}
Iterator valuesIterator() {
return new Itr() {
@SuppressWarnings("unchecked") // values only contains Vs
@Override
V getOutput(int entry) {
return (V) values[entry];
}
};
}
/**
* Ensures that this {@code CompactHashMap} has the smallest representation in memory, given its
* current size.
*/
public void trimToSize() {
if (needsAllocArrays()) {
return;
}
int size = this.size;
if (size < entries.length) {
resizeEntries(size);
}
int minimumTableSize = Hashing.closedTableSize(size, LOAD_FACTOR);
if (minimumTableSize < table.length) {
resizeTable(minimumTableSize);
}
}
@Override
public void clear() {
if (needsAllocArrays()) {
return;
}
modCount++;
Arrays.fill(keys, 0, size, null);
Arrays.fill(values, 0, size, null);
Arrays.fill(table, UNSET);
Arrays.fill(entries, 0, size, UNSET);
this.size = 0;
}
private void writeObject(ObjectOutputStream stream) throws IOException {
stream.defaultWriteObject();
stream.writeInt(size);
for (int i = firstEntryIndex(); i >= 0; i = getSuccessor(i)) {
stream.writeObject(keys[i]);
stream.writeObject(values[i]);
}
}
@SuppressWarnings("unchecked")
private void readObject(ObjectInputStream stream) throws IOException, ClassNotFoundException {
stream.defaultReadObject();
int elementCount = stream.readInt();
if (elementCount < 0) {
throw new InvalidObjectException("Invalid size: " + elementCount);
}
init(elementCount);
for (int i = 0; i < elementCount; i++) {
K key = (K) stream.readObject();
V value = (V) stream.readObject();
put(key, value);
}
}
}