com.google.common.collect.CompactHashSet 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 java.io.IOException;
import java.io.InvalidObjectException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.Serializable;
import java.util.AbstractSet;
import java.util.Arrays;
import java.util.Collection;
import java.util.Collections;
import java.util.ConcurrentModificationException;
import java.util.Iterator;
import java.util.NoSuchElementException;
import org.checkerframework.checker.nullness.compatqual.MonotonicNonNullDecl;
import org.checkerframework.checker.nullness.compatqual.NullableDecl;
/**
* CompactHashSet is an implementation of a Set. All optional operations (adding and removing) are
* supported. The elements can be any objects.
*
* {@code contains(x)}, {@code add(x)} and {@code remove(x)}, 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.HashSet}, 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 only depends on a fixed number of arrays; {@code
* add(x)} operations do not create objects for the garbage collector to deal with, and for
* every element added, the garbage collector will have to traverse {@code 1.5} references on
* average, in the marking phase, not {@code 5.0} as in {@code java.util.HashSet}.
*
*
If there are no removals, then {@link #iterator iteration} order 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.HashSet}.
* 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 Dimitris Andreou
*/
@GwtIncompatible // not worth using in GWT for now
class CompactHashSet extends AbstractSet implements Serializable {
// TODO(user): cache all field accesses in local vars
/** Creates an empty {@code CompactHashSet} instance. */
public static CompactHashSet create() {
return new CompactHashSet<>();
}
/**
* Creates a mutable {@code CompactHashSet} instance containing the elements of the given
* collection in unspecified order.
*
* @param collection the elements that the set should contain
* @return a new {@code CompactHashSet} containing those elements (minus duplicates)
*/
public static CompactHashSet create(Collection collection) {
CompactHashSet set = createWithExpectedSize(collection.size());
set.addAll(collection);
return set;
}
/**
* Creates a mutable {@code CompactHashSet} instance containing the given elements in
* unspecified order.
*
* @param elements the elements that the set should contain
* @return a new {@code CompactHashSet} containing those elements (minus duplicates)
*/
public static CompactHashSet create(E... elements) {
CompactHashSet set = createWithExpectedSize(elements.length);
Collections.addAll(set, elements);
return set;
}
/**
* Creates a {@code CompactHashSet} 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 CompactHashSet} with enough capacity to hold {@code expectedSize}
* elements without resizing
* @throws IllegalArgumentException if {@code expectedSize} is negative
*/
public static CompactHashSet createWithExpectedSize(int expectedSize) {
return new CompactHashSet<>(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
@VisibleForTesting 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 elements 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).
*/
@MonotonicNonNullDecl private transient long[] entries;
/**
* The elements contained in the set, in the range of [0, size()). The elements in [size(),
* elements.length) are all {@code null}.
*/
@MonotonicNonNullDecl transient Object[] elements;
/**
* 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 CompactHashSet}. */
CompactHashSet() {
init(DEFAULT_SIZE);
}
/**
* Constructs a new instance of {@code CompactHashSet} with the specified capacity.
*
* @param expectedSize the initial capacity of this {@code CompactHashSet}.
*/
CompactHashSet(int expectedSize) {
init(expectedSize);
}
/** Pseudoconstructor for serialization support. */
void init(int expectedSize) {
Preconditions.checkArgument(expectedSize >= 0, "Initial capacity 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.elements = 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);
}
@CanIgnoreReturnValue
@Override
public boolean add(@NullableDecl E object) {
if (needsAllocArrays()) {
allocArrays();
}
long[] entries = this.entries;
Object[] elements = this.elements;
int hash = smearedHash(object);
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(object, elements[next])) {
return false;
}
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, object, hash);
this.size = newSize;
int oldCapacity = table.length;
if (Hashing.needsResizing(newEntryIndex, oldCapacity, LOAD_FACTOR)) {
resizeTable(2 * oldCapacity);
}
modCount++;
return true;
}
/**
* Creates a fresh entry with the specified object at the specified position in the entry arrays.
*/
void insertEntry(int entryIndex, E object, int hash) {
this.entries[entryIndex] = ((long) hash << 32) | (NEXT_MASK & UNSET);
this.elements[entryIndex] = object;
}
/** 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.elements = Arrays.copyOf(elements, 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;
}
@Override
public boolean contains(@NullableDecl Object object) {
if (needsAllocArrays()) {
return false;
}
int hash = smearedHash(object);
int next = table[hash & hashTableMask()];
while (next != UNSET) {
long entry = entries[next];
if (getHash(entry) == hash && Objects.equal(object, elements[next])) {
return true;
}
next = getNext(entry);
}
return false;
}
@CanIgnoreReturnValue
@Override
public boolean remove(@NullableDecl Object object) {
if (needsAllocArrays()) {
return false;
}
return remove(object, smearedHash(object));
}
@CanIgnoreReturnValue
private boolean remove(Object object, int hash) {
int tableIndex = hash & hashTableMask();
int next = table[tableIndex];
if (next == UNSET) {
return false;
}
int last = UNSET;
do {
if (getHash(entries[next]) == hash && Objects.equal(object, elements[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 true;
}
last = next;
next = getNext(entries[next]);
} while (next != UNSET);
return false;
}
/**
* 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
elements[dstIndex] = elements[srcIndex];
elements[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 {
elements[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;
}
@Override
public Iterator iterator() {
return new Iterator() {
int expectedModCount = modCount;
int currentIndex = firstEntryIndex();
int indexToRemove = -1;
@Override
public boolean hasNext() {
return currentIndex >= 0;
}
@Override
@SuppressWarnings("unchecked")
public E next() {
checkForConcurrentModification();
if (!hasNext()) {
throw new NoSuchElementException();
}
indexToRemove = currentIndex;
E result = (E) elements[currentIndex];
currentIndex = getSuccessor(currentIndex);
return result;
}
@Override
public void remove() {
checkForConcurrentModification();
checkRemove(indexToRemove >= 0);
expectedModCount++;
CompactHashSet.this.remove(elements[indexToRemove], getHash(entries[indexToRemove]));
currentIndex = adjustAfterRemove(currentIndex, indexToRemove);
indexToRemove = -1;
}
private void checkForConcurrentModification() {
if (modCount != expectedModCount) {
throw new ConcurrentModificationException();
}
}
};
}
@Override
public int size() {
return size;
}
@Override
public boolean isEmpty() {
return size == 0;
}
@Override
public Object[] toArray() {
if (needsAllocArrays()) {
return new Object[0];
}
return Arrays.copyOf(elements, size);
}
@CanIgnoreReturnValue
@Override
public T[] toArray(T[] a) {
if (needsAllocArrays()) {
if (a.length > 0) {
a[0] = null;
}
return a;
}
return ObjectArrays.toArrayImpl(elements, 0, size, a);
}
/**
* Ensures that this {@code CompactHashSet} 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(elements, 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(elements[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++) {
E element = (E) stream.readObject();
add(element);
}
}
}