/*******************************************************************************
* Copyright (c) 2004, 2013 IBM Corporation and others.
* All rights reserved. This program and the accompanying materials
* are made available under the terms of the Eclipse Public License v1.0
* which accompanies this distribution, and is available at
* http://www.eclipse.org/legal/epl-v10.html
*
* Contributors:
* IBM Corporation - initial API and implementation
*******************************************************************************/
package org.eclipse.jdt.internal.core.util;
import java.lang.ref.ReferenceQueue;
import java.lang.ref.WeakReference;
/**
* A hashset whose values can be garbage collected.
*/
@SuppressWarnings({"unchecked", "rawtypes"})
public class WeakHashSet {
public static class HashableWeakReference extends WeakReference {
public int hashCode;
public HashableWeakReference(Object referent, ReferenceQueue queue) {
super(referent, queue);
this.hashCode = referent.hashCode();
}
public boolean equals(Object obj) {
if (!(obj instanceof HashableWeakReference)) return false;
Object referent = get();
Object other = ((HashableWeakReference) obj).get();
if (referent == null) return other == null;
return referent.equals(other);
}
public int hashCode() {
return this.hashCode;
}
public String toString() {
Object referent = get();
if (referent == null) return "[hashCode=" + this.hashCode + "] <referent was garbage collected>"; //$NON-NLS-1$ //$NON-NLS-2$
return "[hashCode=" + this.hashCode + "] " + referent.toString(); //$NON-NLS-1$ //$NON-NLS-2$
}
}
HashableWeakReference[] values;
public int elementSize; // number of elements in the table
int threshold;
ReferenceQueue referenceQueue = new ReferenceQueue();
public WeakHashSet() {
this(5);
}
public WeakHashSet(int size) {
this.elementSize = 0;
this.threshold = size; // size represents the expected number of elements
int extraRoom = (int) (size * 1.75f);
if (this.threshold == extraRoom)
extraRoom++;
this.values = new HashableWeakReference[extraRoom];
}
/*
* Adds the given object to this set.
* If an object that is equals to the given object already exists, do nothing.
* Returns the existing object or the new object if not found.
*/
public Object add(Object obj) {
cleanupGarbageCollectedValues();
int valuesLength = this.values.length,
index = (obj.hashCode() & 0x7FFFFFFF) % valuesLength;
HashableWeakReference currentValue;
while ((currentValue = this.values[index]) != null) {
Object referent;
if (obj.equals(referent = currentValue.get())) {
return referent;
}
if (++index == valuesLength) {
index = 0;
}
}
this.values[index] = new HashableWeakReference(obj, this.referenceQueue);
// assumes the threshold is never equal to the size of the table
if (++this.elementSize > this.threshold)
rehash();
return obj;
}
private void addValue(HashableWeakReference value) {
Object obj = value.get();
if (obj == null) return;
int valuesLength = this.values.length;
int index = (value.hashCode & 0x7FFFFFFF) % valuesLength;
HashableWeakReference currentValue;
while ((currentValue = this.values[index]) != null) {
if (obj.equals(currentValue.get())) {
return;
}
if (++index == valuesLength) {
index = 0;
}
}
this.values[index] = value;
// assumes the threshold is never equal to the size of the table
if (++this.elementSize > this.threshold)
rehash();
}
private void cleanupGarbageCollectedValues() {
HashableWeakReference toBeRemoved;
while ((toBeRemoved = (HashableWeakReference) this.referenceQueue.poll()) != null) {
int hashCode = toBeRemoved.hashCode;
int valuesLength = this.values.length;
int index = (hashCode & 0x7FFFFFFF) % valuesLength;
HashableWeakReference currentValue;
while ((currentValue = this.values[index]) != null) {
if (currentValue == toBeRemoved) {
// replace the value at index with the last value with the same hash
int sameHash = index;
int current;
while ((currentValue = this.values[current = (sameHash + 1) % valuesLength]) != null && currentValue.hashCode == hashCode)
sameHash = current;
this.values[index] = this.values[sameHash];
this.values[sameHash] = null;
this.elementSize--;
break;
}
if (++index == valuesLength) {
index = 0;
}
}
}
}
public boolean contains(Object obj) {
return get(obj) != null;
}
/*
* Return the object that is in this set and that is equals to the given object.
* Return null if not found.
*/
public Object get(Object obj) {
cleanupGarbageCollectedValues();
int valuesLength = this.values.length;
int index = (obj.hashCode() & 0x7FFFFFFF) % valuesLength;
HashableWeakReference currentValue;
while ((currentValue = this.values[index]) != null) {
Object referent;
if (obj.equals(referent = currentValue.get())) {
return referent;
}
if (++index == valuesLength) {
index = 0;
}
}
return null;
}
private void rehash() {
WeakHashSet newHashSet = new WeakHashSet(this.elementSize * 2); // double the number of expected elements
newHashSet.referenceQueue = this.referenceQueue;
HashableWeakReference currentValue;
for (int i = 0, length = this.values.length; i < length; i++)
if ((currentValue = this.values[i]) != null)
newHashSet.addValue(currentValue);
this.values = newHashSet.values;
this.threshold = newHashSet.threshold;
this.elementSize = newHashSet.elementSize;
}
/*
* Removes the object that is in this set and that is equals to the given object.
* Return the object that was in the set, or null if not found.
*/
public Object remove(Object obj) {
cleanupGarbageCollectedValues();
int valuesLength = this.values.length;
int index = (obj.hashCode() & 0x7FFFFFFF) % valuesLength;
HashableWeakReference currentValue;
while ((currentValue = this.values[index]) != null) {
Object referent;
if (obj.equals(referent = currentValue.get())) {
this.elementSize--;
this.values[index] = null;
rehash();
return referent;
}
if (++index == valuesLength) {
index = 0;
}
}
return null;
}
public int size() {
return this.elementSize;
}
public String toString() {
StringBuffer buffer = new StringBuffer("{"); //$NON-NLS-1$
for (int i = 0, length = this.values.length; i < length; i++) {
HashableWeakReference value = this.values[i];
if (value != null) {
Object ref = value.get();
if (ref != null) {
buffer.append(ref.toString());
buffer.append(", "); //$NON-NLS-1$
}
}
}
buffer.append("}"); //$NON-NLS-1$
return buffer.toString();
}
}