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GraalVM is an ecosystem for compiling and running applications written in multiple languages.
GraalVM removes the isolation between programming languages and enables interoperability in a shared runtime.
/*
* Copyright (c) 2017, 2017, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 only, as
* published by the Free Software Foundation. Oracle designates this
* particular file as subject to the "Classpath" exception as provided
* by Oracle in the LICENSE file that accompanied this code.
*
* This code is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
* or visit www.oracle.com if you need additional information or have any
* questions.
*/
package org.graalvm.collections;
import java.util.Iterator;
import java.util.Objects;
import java.util.function.BiFunction;
/**
* Implementation of a map with a memory-efficient structure that always preserves insertion order
* when iterating over keys. Particularly efficient when number of entries is 0 or smaller equal
* {@link #INITIAL_CAPACITY} or smaller 256.
*
* The key/value pairs are kept in an expanding flat object array with keys at even indices and
* values at odd indices. If the map has smaller or equal to {@link #HASH_THRESHOLD} entries, there
* is no additional hash data structure and comparisons are done via linear checking of the
* key/value pairs. For the case where the equality check is particularly cheap (e.g., just an
* object identity comparison), this limit below which the map is without an actual hash table is
* higher and configured at {@link #HASH_THRESHOLD_IDENTITY_COMPARE}.
*
* When the hash table needs to be constructed, the field {@link #hashArray} becomes a new hash
* array where an entry of 0 means no hit and otherwise denotes the entry number in the
* {@link #entries} array. The hash array is interpreted as an actual byte array if the indices fit
* within 8 bit, or as an array of short values if the indices fit within 16 bit, or as an array of
* integer values in other cases.
*
* Hash collisions are handled by chaining a linked list of {@link CollisionLink} objects that take
* the place of the values in the {@link #entries} array.
*
* Removing entries will put {@code null} into the {@link #entries} array. If the occupation of the
* map falls below a specific threshold, the map will be compressed via the
* {@link #maybeCompress(int)} method.
*/
final class EconomicMapImpl implements EconomicMap, EconomicSet {
/**
* Initial number of key/value pair entries that is allocated in the first entries array.
*/
private static final int INITIAL_CAPACITY = 4;
/**
* Maximum number of entries that are moved linearly forward if a key is removed.
*/
private static final int COMPRESS_IMMEDIATE_CAPACITY = 8;
/**
* Minimum number of key/value pair entries added when the entries array is increased in size.
*/
private static final int MIN_CAPACITY_INCREASE = 8;
/**
* Number of entries above which a hash table is created.
*/
private static final int HASH_THRESHOLD = 4;
/**
* Number of entries above which a hash table is created when equality can be checked with
* object identity.
*/
private static final int HASH_THRESHOLD_IDENTITY_COMPARE = 8;
/**
* Maximum number of entries allowed in the map.
*/
private static final int MAX_ELEMENT_COUNT = Integer.MAX_VALUE >> 1;
/**
* Number of entries above which more than 1 byte is necessary for the hash index.
*/
private static final int LARGE_HASH_THRESHOLD = ((1 << Byte.SIZE) << 1);
/**
* Number of entries above which more than 2 bytes are are necessary for the hash index.
*/
private static final int VERY_LARGE_HASH_THRESHOLD = (LARGE_HASH_THRESHOLD << Byte.SIZE);
/**
* Total number of entries (actual entries plus deleted entries).
*/
private int totalEntries;
/**
* Number of deleted entries.
*/
private int deletedEntries;
/**
* Entries array with even indices storing keys and odd indices storing values.
*/
private Object[] entries;
/**
* Hash array that is interpreted either as byte or short or int array depending on number of
* map entries.
*/
private byte[] hashArray;
/**
* The strategy used for comparing keys or {@code null} for denoting special strategy
* {@link Equivalence#IDENTITY}.
*/
private final Equivalence strategy;
/**
* Intercept method for debugging purposes.
*/
private static EconomicMapImpl intercept(EconomicMapImpl map) {
return map;
}
public static EconomicMapImpl create(Equivalence strategy, boolean isSet) {
return intercept(new EconomicMapImpl<>(strategy, isSet));
}
public static EconomicMapImpl create(Equivalence strategy, int initialCapacity, boolean isSet) {
return intercept(new EconomicMapImpl<>(strategy, initialCapacity, isSet));
}
public static EconomicMapImpl create(Equivalence strategy, UnmodifiableEconomicMap other, boolean isSet) {
return intercept(new EconomicMapImpl<>(strategy, other, isSet));
}
public static EconomicMapImpl create(Equivalence strategy, UnmodifiableEconomicSet other, boolean isSet) {
return intercept(new EconomicMapImpl<>(strategy, other, isSet));
}
private EconomicMapImpl(Equivalence strategy, boolean isSet) {
if (strategy == Equivalence.IDENTITY) {
this.strategy = null;
} else {
this.strategy = strategy;
}
this.isSet = isSet;
}
private EconomicMapImpl(Equivalence strategy, int initialCapacity, boolean isSet) {
this(strategy, isSet);
init(initialCapacity);
}
private EconomicMapImpl(Equivalence strategy, UnmodifiableEconomicMap other, boolean isSet) {
this(strategy, isSet);
if (!initFrom(other)) {
init(other.size());
putAll(other);
}
}
private EconomicMapImpl(Equivalence strategy, UnmodifiableEconomicSet other, boolean isSet) {
this(strategy, isSet);
if (!initFrom(other)) {
init(other.size());
addAll(other);
}
}
@SuppressWarnings("unchecked")
private boolean initFrom(Object o) {
if (o instanceof EconomicMapImpl) {
EconomicMapImpl otherMap = (EconomicMapImpl) o;
// We are only allowed to directly copy if the strategies of the two maps are the same.
if (strategy == otherMap.strategy) {
totalEntries = otherMap.totalEntries;
deletedEntries = otherMap.deletedEntries;
if (otherMap.entries != null) {
entries = otherMap.entries.clone();
}
if (otherMap.hashArray != null) {
hashArray = otherMap.hashArray.clone();
}
return true;
}
}
return false;
}
private void init(int size) {
if (size > INITIAL_CAPACITY) {
entries = new Object[size << 1];
}
}
/**
* Links the collisions. Needs to be immutable class for allowing efficient shallow copy from
* other map on construction.
*/
private static final class CollisionLink {
CollisionLink(Object value, int next) {
this.value = value;
this.next = next;
}
final Object value;
/**
* Index plus one of the next entry in the collision link chain.
*/
final int next;
}
@SuppressWarnings("unchecked")
@Override
public V get(K key) {
Objects.requireNonNull(key);
int index = find(key);
if (index != -1) {
return (V) getValue(index);
}
return null;
}
private int find(K key) {
if (hasHashArray()) {
return findHash(key);
} else {
return findLinear(key);
}
}
private int findLinear(K key) {
for (int i = 0; i < totalEntries; i++) {
Object entryKey = entries[i << 1];
if (entryKey != null && compareKeys(key, entryKey)) {
return i;
}
}
return -1;
}
private boolean compareKeys(Object key, Object entryKey) {
if (key == entryKey) {
return true;
}
if (strategy != null && strategy != Equivalence.IDENTITY_WITH_SYSTEM_HASHCODE) {
if (strategy == Equivalence.DEFAULT) {
return key.equals(entryKey);
} else {
return strategy.equals(key, entryKey);
}
}
return false;
}
private int findHash(K key) {
int index = getHashArray(getHashIndex(key)) - 1;
if (index != -1) {
Object entryKey = getKey(index);
if (compareKeys(key, entryKey)) {
return index;
} else {
Object entryValue = getRawValue(index);
if (entryValue instanceof CollisionLink) {
return findWithCollision(key, (CollisionLink) entryValue);
}
}
}
return -1;
}
private int findWithCollision(K key, CollisionLink initialEntryValue) {
int index;
Object entryKey;
CollisionLink entryValue = initialEntryValue;
while (true) {
CollisionLink collisionLink = entryValue;
index = collisionLink.next;
entryKey = getKey(index);
if (compareKeys(key, entryKey)) {
return index;
} else {
Object value = getRawValue(index);
if (value instanceof CollisionLink) {
entryValue = (CollisionLink) getRawValue(index);
} else {
return -1;
}
}
}
}
private int getHashArray(int index) {
if (entries.length < LARGE_HASH_THRESHOLD) {
return (hashArray[index] & 0xFF);
} else if (entries.length < VERY_LARGE_HASH_THRESHOLD) {
int adjustedIndex = index << 1;
return (hashArray[adjustedIndex] & 0xFF) | ((hashArray[adjustedIndex + 1] & 0xFF) << 8);
} else {
int adjustedIndex = index << 2;
return (hashArray[adjustedIndex] & 0xFF) | ((hashArray[adjustedIndex + 1] & 0xFF) << 8) | ((hashArray[adjustedIndex + 2] & 0xFF) << 16) | ((hashArray[adjustedIndex + 3] & 0xFF) << 24);
}
}
private void setHashArray(int index, int value) {
if (entries.length < LARGE_HASH_THRESHOLD) {
hashArray[index] = (byte) value;
} else if (entries.length < VERY_LARGE_HASH_THRESHOLD) {
int adjustedIndex = index << 1;
hashArray[adjustedIndex] = (byte) value;
hashArray[adjustedIndex + 1] = (byte) (value >> 8);
} else {
int adjustedIndex = index << 2;
hashArray[adjustedIndex] = (byte) value;
hashArray[adjustedIndex + 1] = (byte) (value >> 8);
hashArray[adjustedIndex + 2] = (byte) (value >> 16);
hashArray[adjustedIndex + 3] = (byte) (value >> 24);
}
}
private int findAndRemoveHash(Object key) {
int hashIndex = getHashIndex(key);
int index = getHashArray(hashIndex) - 1;
if (index != -1) {
Object entryKey = getKey(index);
if (compareKeys(key, entryKey)) {
Object value = getRawValue(index);
int nextIndex = -1;
if (value instanceof CollisionLink) {
CollisionLink collisionLink = (CollisionLink) value;
nextIndex = collisionLink.next;
}
setHashArray(hashIndex, nextIndex + 1);
return index;
} else {
Object entryValue = getRawValue(index);
if (entryValue instanceof CollisionLink) {
return findAndRemoveWithCollision(key, (CollisionLink) entryValue, index);
}
}
}
return -1;
}
private int findAndRemoveWithCollision(Object key, CollisionLink initialEntryValue, int initialIndexValue) {
int index;
Object entryKey;
CollisionLink entryValue = initialEntryValue;
int lastIndex = initialIndexValue;
while (true) {
CollisionLink collisionLink = entryValue;
index = collisionLink.next;
entryKey = getKey(index);
if (compareKeys(key, entryKey)) {
Object value = getRawValue(index);
if (value instanceof CollisionLink) {
CollisionLink thisCollisionLink = (CollisionLink) value;
setRawValue(lastIndex, new CollisionLink(collisionLink.value, thisCollisionLink.next));
} else {
setRawValue(lastIndex, collisionLink.value);
}
return index;
} else {
Object value = getRawValue(index);
if (value instanceof CollisionLink) {
entryValue = (CollisionLink) getRawValue(index);
lastIndex = index;
} else {
return -1;
}
}
}
}
private int getHashIndex(Object key) {
int hash;
if (strategy != null && strategy != Equivalence.DEFAULT) {
if (strategy == Equivalence.IDENTITY_WITH_SYSTEM_HASHCODE) {
hash = System.identityHashCode(key);
} else {
hash = strategy.hashCode(key);
}
} else {
hash = key.hashCode();
}
hash = hash ^ (hash >>> 16);
return hash & (getHashTableSize() - 1);
}
@SuppressWarnings("unchecked")
@Override
public V put(K key, V value) {
if (key == null) {
throw new UnsupportedOperationException("null not supported as key!");
}
int index = find(key);
if (index != -1) {
Object oldValue = getValue(index);
setValue(index, value);
return (V) oldValue;
}
int nextEntryIndex = totalEntries;
if (entries == null) {
entries = new Object[INITIAL_CAPACITY << 1];
} else if (entries.length == nextEntryIndex << 1) {
grow();
assert entries.length > totalEntries << 1;
// Can change if grow is actually compressing.
nextEntryIndex = totalEntries;
}
setKey(nextEntryIndex, key);
setValue(nextEntryIndex, value);
totalEntries++;
if (hasHashArray()) {
// Rehash on collision if hash table is more than three quarters full.
boolean rehashOnCollision = (getHashTableSize() < (size() + (size() >> 1)));
putHashEntry(key, nextEntryIndex, rehashOnCollision);
} else if (totalEntries > getHashThreshold()) {
createHash();
}
return null;
}
/**
* Number of entries above which a hash table should be constructed.
*/
private int getHashThreshold() {
if (strategy == null || strategy == Equivalence.IDENTITY_WITH_SYSTEM_HASHCODE) {
return HASH_THRESHOLD_IDENTITY_COMPARE;
} else {
return HASH_THRESHOLD;
}
}
private void grow() {
int entriesLength = entries.length;
int newSize = (entriesLength >> 1) + Math.max(MIN_CAPACITY_INCREASE, entriesLength >> 2);
if (newSize > MAX_ELEMENT_COUNT) {
throw new UnsupportedOperationException("map grown too large!");
}
Object[] newEntries = new Object[newSize << 1];
System.arraycopy(entries, 0, newEntries, 0, entriesLength);
entries = newEntries;
if ((entriesLength < LARGE_HASH_THRESHOLD && newEntries.length >= LARGE_HASH_THRESHOLD) ||
(entriesLength < VERY_LARGE_HASH_THRESHOLD && newEntries.length > VERY_LARGE_HASH_THRESHOLD)) {
// Rehash in order to change number of bits reserved for hash indices.
createHash();
}
}
/**
* Compresses the graph if there is a large number of deleted entries and returns the translated
* new next index.
*/
private int maybeCompress(int nextIndex) {
if (entries.length != INITIAL_CAPACITY << 1 && deletedEntries >= (totalEntries >> 1) + (totalEntries >> 2)) {
return compressLarge(nextIndex);
}
return nextIndex;
}
/**
* Compresses the graph and returns the translated new next index.
*/
private int compressLarge(int nextIndex) {
int size = INITIAL_CAPACITY;
int remaining = totalEntries - deletedEntries;
while (size <= remaining) {
size += Math.max(MIN_CAPACITY_INCREASE, size >> 1);
}
Object[] newEntries = new Object[size << 1];
int z = 0;
int newNextIndex = remaining;
for (int i = 0; i < totalEntries; ++i) {
Object key = getKey(i);
if (i == nextIndex) {
newNextIndex = z;
}
if (key != null) {
newEntries[z << 1] = key;
newEntries[(z << 1) + 1] = getValue(i);
z++;
}
}
this.entries = newEntries;
totalEntries = z;
deletedEntries = 0;
if (z <= getHashThreshold()) {
this.hashArray = null;
} else {
createHash();
}
return newNextIndex;
}
private int getHashTableSize() {
if (entries.length < LARGE_HASH_THRESHOLD) {
return hashArray.length;
} else if (entries.length < VERY_LARGE_HASH_THRESHOLD) {
return hashArray.length >> 1;
} else {
return hashArray.length >> 2;
}
}
private void createHash() {
int entryCount = size();
// Calculate smallest 2^n that is greater number of entries.
int size = getHashThreshold();
while (size <= entryCount) {
size <<= 1;
}
// Give extra size to avoid collisions.
size <<= 1;
if (this.entries.length >= VERY_LARGE_HASH_THRESHOLD) {
// Every entry has 4 bytes.
size <<= 2;
} else if (this.entries.length >= LARGE_HASH_THRESHOLD) {
// Every entry has 2 bytes.
size <<= 1;
} else {
// Entries are very small => give extra size to further reduce collisions.
size <<= 1;
}
hashArray = new byte[size];
for (int i = 0; i < totalEntries; i++) {
Object entryKey = getKey(i);
if (entryKey != null) {
putHashEntry(entryKey, i, false);
}
}
}
private void putHashEntry(Object key, int entryIndex, boolean rehashOnCollision) {
int hashIndex = getHashIndex(key);
int oldIndex = getHashArray(hashIndex) - 1;
if (oldIndex != -1 && rehashOnCollision) {
this.createHash();
return;
}
setHashArray(hashIndex, entryIndex + 1);
Object value = getRawValue(entryIndex);
if (oldIndex != -1) {
assert entryIndex != oldIndex : "this cannot happend and would create an endless collision link cycle";
if (value instanceof CollisionLink) {
CollisionLink collisionLink = (CollisionLink) value;
setRawValue(entryIndex, new CollisionLink(collisionLink.value, oldIndex));
} else {
setRawValue(entryIndex, new CollisionLink(getRawValue(entryIndex), oldIndex));
}
} else {
if (value instanceof CollisionLink) {
CollisionLink collisionLink = (CollisionLink) value;
setRawValue(entryIndex, collisionLink.value);
}
}
}
@Override
public int size() {
return totalEntries - deletedEntries;
}
@Override
public boolean containsKey(K key) {
return find(key) != -1;
}
@Override
public void clear() {
entries = null;
hashArray = null;
totalEntries = deletedEntries = 0;
}
private boolean hasHashArray() {
return hashArray != null;
}
@SuppressWarnings("unchecked")
@Override
public V removeKey(K key) {
if (key == null) {
throw new UnsupportedOperationException("null not supported as key!");
}
int index;
if (hasHashArray()) {
index = this.findAndRemoveHash(key);
} else {
index = this.findLinear(key);
}
if (index != -1) {
Object value = getValue(index);
remove(index);
return (V) value;
}
return null;
}
/**
* Removes the element at the specific index and returns the index of the next element. This can
* be a different value if graph compression was triggered.
*/
private int remove(int indexToRemove) {
int index = indexToRemove;
int entriesAfterIndex = totalEntries - index - 1;
int result = index + 1;
// Without hash array, compress immediately.
if (entriesAfterIndex <= COMPRESS_IMMEDIATE_CAPACITY && !hasHashArray()) {
while (index < totalEntries - 1) {
setKey(index, getKey(index + 1));
setRawValue(index, getRawValue(index + 1));
index++;
}
result--;
}
setKey(index, null);
setRawValue(index, null);
if (index == totalEntries - 1) {
// Make sure last element is always non-null.
totalEntries--;
while (index > 0 && getKey(index - 1) == null) {
totalEntries--;
deletedEntries--;
index--;
}
} else {
deletedEntries++;
result = maybeCompress(result);
}
return result;
}
private abstract class SparseMapIterator implements Iterator {
protected int current;
@Override
public boolean hasNext() {
return current < totalEntries;
}
@Override
public void remove() {
if (hasHashArray()) {
EconomicMapImpl.this.findAndRemoveHash(getKey(current - 1));
}
current = EconomicMapImpl.this.remove(current - 1);
}
}
@Override
public Iterable getValues() {
return new Iterable() {
@Override
public Iterator iterator() {
return new SparseMapIterator() {
@SuppressWarnings("unchecked")
@Override
public V next() {
Object result;
while (true) {
result = getValue(current);
if (result == null && getKey(current) == null) {
// values can be null, double-check if key is also null
current++;
} else {
current++;
break;
}
}
return (V) result;
}
};
}
};
}
@Override
public Iterable getKeys() {
return this;
}
@Override
public boolean isEmpty() {
return this.size() == 0;
}
@Override
public MapCursor getEntries() {
return new MapCursor() {
int current = -1;
@Override
public boolean advance() {
current++;
if (current >= totalEntries) {
return false;
} else {
while (EconomicMapImpl.this.getKey(current) == null) {
// Skip over null entries
current++;
}
return true;
}
}
@SuppressWarnings("unchecked")
@Override
public K getKey() {
return (K) EconomicMapImpl.this.getKey(current);
}
@SuppressWarnings("unchecked")
@Override
public V getValue() {
return (V) EconomicMapImpl.this.getValue(current);
}
@Override
public void remove() {
if (hasHashArray()) {
EconomicMapImpl.this.findAndRemoveHash(EconomicMapImpl.this.getKey(current));
}
current = EconomicMapImpl.this.remove(current) - 1;
}
};
}
@SuppressWarnings("unchecked")
@Override
public void replaceAll(BiFunction function) {
for (int i = 0; i < totalEntries; i++) {
Object entryKey = getKey(i);
if (entryKey != null) {
Object newValue = function.apply((K) entryKey, (V) getValue(i));
setValue(i, newValue);
}
}
}
private Object getKey(int index) {
return entries[index << 1];
}
private void setKey(int index, Object newValue) {
entries[index << 1] = newValue;
}
private void setValue(int index, Object newValue) {
Object oldValue = getRawValue(index);
if (oldValue instanceof CollisionLink) {
CollisionLink collisionLink = (CollisionLink) oldValue;
setRawValue(index, new CollisionLink(newValue, collisionLink.next));
} else {
setRawValue(index, newValue);
}
}
private void setRawValue(int index, Object newValue) {
entries[(index << 1) + 1] = newValue;
}
private Object getRawValue(int index) {
return entries[(index << 1) + 1];
}
private Object getValue(int index) {
Object object = getRawValue(index);
if (object instanceof CollisionLink) {
return ((CollisionLink) object).value;
}
return object;
}
private final boolean isSet;
@Override
public String toString() {
StringBuilder builder = new StringBuilder();
builder.append(isSet ? "set(size=" : "map(size=").append(size()).append(", {");
String sep = "";
MapCursor cursor = getEntries();
while (cursor.advance()) {
builder.append(sep);
if (isSet) {
builder.append(cursor.getKey());
} else {
builder.append("(").append(cursor.getKey()).append(",").append(cursor.getValue()).append(")");
}
sep = ",";
}
builder.append("})");
return builder.toString();
}
@Override
public Iterator iterator() {
return new SparseMapIterator() {
@SuppressWarnings("unchecked")
@Override
public K next() {
Object result;
while ((result = getKey(current++)) == null) {
// skip null entries
}
return (K) result;
}
};
}
@Override
public boolean contains(K element) {
return containsKey(element);
}
@SuppressWarnings("unchecked")
@Override
public boolean add(K element) {
return put(element, (V) element) == null;
}
@Override
public void remove(K element) {
removeKey(element);
}
}