/*
* Copyright Terracotta, Inc.
*
* 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 org.ehcache.core.collections;
import java.lang.ref.Reference;
import java.lang.ref.ReferenceQueue;
import java.util.AbstractMap.SimpleEntry;
import java.util.AbstractSet;
import java.util.Collection;
import java.util.Iterator;
import java.util.Map;
import java.util.Set;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;
/**
* @author Alex Snaps
*/
public class ConcurrentWeakIdentityHashMap<K, V> implements ConcurrentMap<K, V> {
private final ConcurrentMap<WeakReference<K>, V> map = new ConcurrentHashMap<WeakReference<K>, V>();
private final ReferenceQueue<K> queue = new ReferenceQueue<K>();
@Override
public V putIfAbsent(final K key, final V value) {
purgeKeys();
return map.putIfAbsent(newKey(key), value);
}
@Override
public boolean remove(final Object key, final Object value) {
purgeKeys();
return map.remove(new WeakReference<Object>( key, null), value);
}
@Override
public boolean replace(final K key, final V oldValue, final V newValue) {
purgeKeys();
return map.replace(newKey(key), oldValue, newValue);
}
@Override
public V replace(final K key, final V value) {
purgeKeys();
return map.replace(newKey(key), value);
}
@Override
public int size() {
purgeKeys();
return map.size();
}
@Override
public boolean isEmpty() {
purgeKeys();
return map.isEmpty();
}
@Override
public boolean containsKey(final Object key) {
purgeKeys();
return map.containsKey(new WeakReference<Object>(key, null));
}
@Override
public boolean containsValue(final Object value) {
purgeKeys();
return map.containsValue(value);
}
@Override
public V get(final Object key) {
purgeKeys();
return map.get(new WeakReference<Object>(key, null));
}
@Override
public V put(final K key, final V value) {
purgeKeys();
return map.put(newKey(key), value);
}
@Override
public V remove(final Object key) {
purgeKeys();
return map.remove(new WeakReference<Object>(key, null));
}
@Override
public void putAll(final Map<? extends K, ? extends V> m) {
purgeKeys();
for (Entry<? extends K, ? extends V> entry : m.entrySet()) {
map.put(newKey(entry.getKey()), entry.getValue());
}
}
@Override
public void clear() {
purgeKeys();
map.clear();
}
@Override
public Set<K> keySet() {
return new AbstractSet<K>() {
@Override
public Iterator<K> iterator() {
purgeKeys();
return new WeakSafeIterator<K, WeakReference<K>>(map.keySet().iterator()) {
@Override
protected K extract(WeakReference<K> u) {
return u.get();
}
};
}
@Override
public boolean contains(Object o) {
return ConcurrentWeakIdentityHashMap.this.containsKey(o);
}
@Override
public int size() {
return map.size();
}
};
}
@Override
public Collection<V> values() {
purgeKeys();
return map.values();
}
@Override
public Set<Entry<K, V>> entrySet() {
return new AbstractSet<Entry<K, V>>() {
@Override
public Iterator<Entry<K, V>> iterator() {
purgeKeys();
return new WeakSafeIterator<Entry<K, V>, Entry<WeakReference<K>, V>>(map.entrySet().iterator()) {
@Override
protected Entry<K, V> extract(Entry<WeakReference<K>, V> u) {
K key = u.getKey().get();
if (key == null) {
return null;
} else {
return new SimpleEntry<K, V>(key, u.getValue());
}
}
};
}
@Override
public int size() {
return map.size();
}
};
}
private void purgeKeys() {
Reference<? extends K> reference;
while ((reference = queue.poll()) != null) {
map.remove(reference);
}
}
private WeakReference<K> newKey(final K key) {
return new WeakReference<K>(key, queue);
}
private static class WeakReference<T> extends java.lang.ref.WeakReference<T> {
private final int hashCode;
private WeakReference(final T referent, final ReferenceQueue<? super T> q) {
super(referent, q);
hashCode = referent.hashCode();
}
@Override
public boolean equals(final Object obj) {
return obj != null && obj.getClass() == this.getClass() && (this == obj || this.get() == ((WeakReference)obj).get());
}
@Override
public int hashCode() {
return hashCode;
}
}
private static abstract class WeakSafeIterator<T, U> implements Iterator<T> {
private final Iterator<U> weakIterator;
protected T strongNext;
public WeakSafeIterator(Iterator<U> weakIterator) {
this.weakIterator = weakIterator;
advance();
}
private void advance() {
while (weakIterator.hasNext()) {
U nextU = weakIterator.next();
if ((strongNext = extract(nextU)) != null) {
return;
}
}
strongNext = null;
}
@Override
public boolean hasNext() {
return strongNext != null;
}
@Override
public final T next() {
T next = strongNext;
advance();
return next;
}
@Override
public void remove() {
throw new UnsupportedOperationException();
}
protected abstract T extract(U u);
}
}