org.jruby.util.WeakIdentityHashMap Maven / Gradle / Ivy
/***** BEGIN LICENSE BLOCK *****
* Version: EPL 1.0/GPL 2.0/LGPL 2.1
*
* The contents of this file are subject to the Eclipse Public
* License Version 1.0 (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.eclipse.org/legal/epl-v10.html
*
* Software distributed under the License is distributed on an "AS
* IS" basis, WITHOUT WARRANTY OF ANY KIND, either express or
* implied. See the License for the specific language governing
* rights and limitations under the License.
*
* Copyright (C) 2006 Kresten Krab Thorup
*
* Alternatively, the contents of this file may be used under the terms of
* either of the GNU General Public License Version 2 or later (the "GPL"),
* or the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
* in which case the provisions of the GPL or the LGPL are applicable instead
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package org.jruby.util;
import java.lang.ref.ReferenceQueue;
import java.lang.ref.WeakReference;
import java.util.Iterator;
import java.util.Map;
import java.util.NoSuchElementException;
/**
* Class WeakIdentityHashMap is a hash map that hashes
* objects based on System.identityHashMap, and holds weakly onto the
* key. This fails if values make reference to the keys!
*
* @author Kresten Krab Thorup
* @version 2.0
* @since 1.0
*/
public class WeakIdentityHashMap extends GenericMap implements Map {
private static final float DEFAULT_RATIO = 0.75F;
private static final Object NULL_KEY = new Object();
private final ReferenceQueue queue = new ReferenceQueue();
private static Object unmaskKey(Object key) {
if (key == NULL_KEY) {
return null;
} else {
return key;
}
}
private Object maskKey(Object key) {
if (key == null) {
return NULL_KEY;
} else {
return key;
}
}
class Entry extends WeakReference implements Map.Entry {
private final int key_hash;
private Entry next;
private Object value;
@Override
public int hashCode() {
return key_hash ^ valueHash(getValue());
}
@Override
public boolean equals(Object other) {
if (other instanceof Map.Entry) {
Map.Entry ent = (Map.Entry) other;
return getKey() == ent.getKey()
&& valueEquals(getValue(), ent.getValue());
} else {
return false;
}
}
Entry(int key_hash, Object masked_key, Object value, Entry next, ReferenceQueue q) {
super(masked_key, q);
this.key_hash = key_hash;
this.value = value;
this.next = next;
}
Object getMaskedKey() {
return super.get();
}
public Object getKey() {
return unmaskKey(getMaskedKey());
}
public Object getValue() {
return value;
}
public Object setValue(Object value) {
Object result = this.value;
this.value = value;
return result;
}
boolean sameKey(int hash, Object masked_key) {
return getMaskedKey() == masked_key;
}
}
/** the hash index */
private Entry[] table;
/** the current range for table. */
private int range;
private float ratio;
/** translate hash code bucket to index */
private int index(int hash) {
return (hash & 0x7ffffff) % range;
}
/** the default and only constructor */
public WeakIdentityHashMap() {
clear(3);
}
public WeakIdentityHashMap(int size) {
clear(Math.max(3, Math.round(size/DEFAULT_RATIO)));
}
public void clear() {
clear(3);
}
private void clear(int size) {
range = size;
this.size = 0;
ratio = DEFAULT_RATIO;
table = new Entry[range];
}
private void expunge() {
Entry e;
while ((e = (Entry) queue.poll()) != null) {
removeEntry(e);
}
}
/** return the element with the given key */
public Object get(Object key) {
Object masked_key = maskKey(key);
int hash = keyHash(masked_key);
return get(hash, masked_key);
}
private Object get(int hash, Object masked_key) {
int idx = index(hash);
expunge();
for (Entry ent = table[idx]; ent != null; ent = ent.next) {
if (ent.sameKey(hash, masked_key)) {
return ent.value;
}
}
return null;
}
/** return the element with the given key */
@Override
public boolean containsKey(Object key) {
Object masked_key = maskKey(key);
int hash = keyHash(masked_key);
return containsKey(hash, masked_key);
}
private boolean containsKey(int hash, Object masked_key) {
int idx = index(hash);
expunge();
for (Entry ent = table[idx]; ent != null; ent = ent.next) {
if (ent.sameKey(hash, masked_key)) {
return true;
}
}
return false;
}
public Object put(Object key, Object value) {
Object masked_key = maskKey(key);
int hash = keyHash(masked_key);
return put(hash, masked_key, value);
}
private Object put(int hash, Object masked_key, Object value) {
int idx = index(hash);
for (Entry ent = table[idx]; ent != null; ent = ent.next) {
if (ent.sameKey(hash, masked_key)) {
return ent.setValue(value);
}
}
expunge();
if (1.0F * size / range > ratio) {
grow();
idx = index(hash);
}
table[idx] = new Entry(hash, masked_key, value, table[idx], queue);
size += 1;
return null;
}
public Object remove(Object key) {
key = maskKey(key);
int hash = keyHash(key);
return remove(hash, key);
}
public Object remove(int hash, Object key) {
key = maskKey(key);
int idx = index(hash);
Entry entry = table[idx];
if (entry != null) {
if (entry.sameKey(hash, key)) {
table[idx] = entry.next;
size -= 1;
return entry.getValue();
} else {
Entry ahead = entry.next;
while (ahead != null) {
if (ahead.sameKey(hash, key)) {
entry.next = ahead.next;
size -= 1;
return ahead.getValue();
}
entry = ahead;
ahead = ahead.next;
}
}
}
// it was not found at all!
return null;
}
private void removeEntry(Entry ent) {
int idx = index(ent.key_hash);
Entry entry = table[idx];
if (entry != null) {
if (entry == ent) {
table[idx] = entry.next;
size -= 1;
return;
} else {
Entry ahead = entry.next;
while (ahead != null) {
if (ahead == ent) {
entry.next = ahead.next;
size -= 1;
return;
}
entry = ahead;
ahead = ahead.next;
}
}
}
valueRemoved(ent.value);
}
// can be overridden to be informed when objects are removed
protected void valueRemoved(Object value) {
}
private void grow() {
int old_range = range;
Entry[] old_table = table;
range = old_range * 2 + 1;
table = new Entry[range];
for (int i = 0; i < old_range; i++) {
Entry entry = old_table[i];
while (entry != null) {
Entry ahead = entry.next;
int idx = index(entry.key_hash);
entry.next = table[idx];
table[idx] = entry;
entry = ahead;
}
}
}
final class EntryIterator implements Iterator {
private int idx;
private Entry entry;
EntryIterator() {
idx = 0;
expunge();
entry = table[0];
locateNext();
}
private void locateNext() {
// we reached the end of a list
while (entry == null) {
// goto next bucket
idx += 1;
if (idx == range) {
// we reached the end
return;
}
// entry is the first element of this bucket
entry = table[idx];
}
}
public boolean hasNext() {
return (entry != null);
}
public Object next() {
Object result = entry;
if (result == null) {
throw new NoSuchElementException();
} else {
entry = entry.next;
locateNext();
return result;
}
}
public void remove() {
Entry remove = entry;
expunge();
entry = entry.next;
locateNext();
WeakIdentityHashMap.this.removeEntry(remove);
}
}
protected Iterator entryIterator() {
return new EntryIterator();
}
@Override
protected final int keyHash(Object key) {
return System.identityHashCode(key);
}
@Override
protected final boolean keyEquals(Object key1, Object key2) {
return key1 == key2;
}
@Override
public int size() {
expunge();
return super.size();
}
@Override
public boolean isEmpty() {
return size() == 0;
}
}
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