/*
* @(#)$Id: codetemplate_xbird.xml 943 2006-09-13 07:03:37Z yui $
*
* Copyright 2006-2008 Makoto YUI
*
* 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.
*
* Contributors:
* Makoto YUI - initial implementation
*/
package xbird.util.cache;
import xbird.util.concurrent.counter.UnsafeIntCounter;
import xbird.util.concurrent.lock.AtomicBackoffLock;
import xbird.util.concurrent.lock.ILock;
import xbird.util.lang.PrivilegedAccessor;
import xbird.util.lang.UnsafeUtils;
/**
*
* <DIV lang="en"></DIV>
* <DIV lang="ja"></DIV>
*
* @author Makoto YUI (yuin405+xbird@gmail.com)
*/
public class CacheEntry<K, V> implements ICacheEntry<K, V> {
private static final long serialVersionUID = 962426580970946876L;
//TODO should use AtomicFieldReferenceUpdater?
private static final sun.misc.Unsafe unsafe = UnsafeUtils.getUnsafe();
private static final long valueOffset = unsafe.objectFieldOffset(PrivilegedAccessor.getField(CacheEntry.class, "_value"));
protected int _index = -1;
protected final K _key;
protected V _value;
private final int _hash;
protected final UnsafeIntCounter _pinning;
private final ILock _lock = new AtomicBackoffLock();
/** used for barrier */
private volatile int _macguffin;
public CacheEntry(K key, V value) {
this(key, value, true);
}
public CacheEntry(K key, V value, boolean pin) {
this._key = key;
this._value = value;
this._hash = (key == null) ? -1 : _key.hashCode();
this._pinning = new UnsafeIntCounter(pin ? 1 : 0);
this._macguffin = 0;
}
public void setIndex(int index) {
this._index = index;
}
public final int getIndex() {
return _index;
}
public final K getKey() {
return _key;
}
public final V getValue() {
return _value;
}
public final V volatileGetValue() {
int lfence = _macguffin;
return _value;
//return <V> unsafe.getObjectVolatile(this, valueOffset);
}
public void setValue(final V newValue) {
this._value = newValue;
}
public final void volatileSetValue(final V newValue) {
this._value = newValue;
this._macguffin = 0; // sfence
}
public final boolean compareAndSetValue(final V expect, final V update) {
return unsafe.compareAndSwapObject(this, valueOffset, expect, update);
}
@Override
public final int hashCode() {
return _hash;
}
@Override
public boolean equals(Object obj) {
if(obj == this) {
return true;
}
if(obj == null || obj.hashCode() != _hash) {
return false;
}
if(obj instanceof CacheEntry) {
final CacheEntry e = (CacheEntry) obj;
return e.getValue() == _value && e.getKey() == _key;
}
return false;
}
public boolean pin() {
final UnsafeIntCounter pinning = _pinning;
int capa;
do {
capa = pinning.get();
if(capa == -1) {// does not pin when the entry is evicted
return false;
}
} while(!pinning.compareAndSet(capa, capa + 1));
return true;
}
public final void unpin() {
_pinning.decrementAndGet();
}
public final boolean isPinned() {
return _pinning.get() > 0;
}
public final int pinCount() {
return _pinning.get();
}
public void setEvicted() {
_pinning.set(-1);
}
public void tryEvict(int expect, int update) {
_pinning.compareAndSet(expect, update);
}
public boolean tryEvict() {
return _pinning.compareAndSet(0, -1);
}
public boolean isEvicted() {
return _pinning.get() == -1;
}
public final ILock lock() {
return _lock;
}
}