/*
* Copyright 2014 Attila Szegedi, Daniel Dekany, Jonathan Revusky
*
* 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 freemarker.cache;
import java.lang.ref.Reference;
import java.lang.ref.ReferenceQueue;
import java.lang.ref.SoftReference;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.util.Map;
import freemarker.core._ConcurrentMapFactory;
import freemarker.template.utility.UndeclaredThrowableException;
/**
* Soft cache storage is a cache storage that uses {@link SoftReference}
* objects to hold the objects it was passed, therefore allows the garbage
* collector to purge the cache when it determines that it wants to free up
* memory.
* This class is thread-safe to the extent that its underlying map is. The
* default implementation uses a concurrent map on Java 5 and above, so it's
* thread-safe in that case.
*
* @see freemarker.template.Configuration#setCacheStorage(CacheStorage)
*/
public class SoftCacheStorage implements ConcurrentCacheStorage, CacheStorageWithGetSize
{
private static final Method atomicRemove = getAtomicRemoveMethod();
private final ReferenceQueue queue = new ReferenceQueue();
private final Map map;
private final boolean concurrent;
public SoftCacheStorage() {
this(_ConcurrentMapFactory.newMaybeConcurrentHashMap());
}
public boolean isConcurrent() {
return concurrent;
}
public SoftCacheStorage(Map backingMap) {
map = backingMap;
this.concurrent = _ConcurrentMapFactory.isConcurrent(map);
}
public Object get(Object key) {
processQueue();
Reference ref = (Reference)map.get(key);
return ref == null ? null : ref.get();
}
public void put(Object key, Object value) {
processQueue();
map.put(key, new SoftValueReference(key, value, queue));
}
public void remove(Object key) {
processQueue();
map.remove(key);
}
public void clear() {
map.clear();
processQueue();
}
/**
* Returns a close approximation of the number of cache entries.
*
* @since 2.3.21
*/
public int getSize() {
processQueue();
return map.size();
}
private void processQueue() {
for(;;) {
SoftValueReference ref = (SoftValueReference)queue.poll();
if(ref == null) {
return;
}
Object key = ref.getKey();
if(concurrent) {
try {
atomicRemove.invoke(map, new Object[] { key, ref });
}
catch(IllegalAccessException e) {
throw new UndeclaredThrowableException(e);
}
catch(InvocationTargetException e) {
throw new UndeclaredThrowableException(e);
}
}
else if(map.get(key) == ref) {
map.remove(key);
}
}
}
private static final class SoftValueReference extends SoftReference {
private final Object key;
SoftValueReference(Object key, Object value, ReferenceQueue queue) {
super(value, queue);
this.key = key;
}
Object getKey() {
return key;
}
}
private static Method getAtomicRemoveMethod() {
try {
return Class.forName("java.util.concurrent.ConcurrentMap").getMethod("remove", new Class[] { Object.class, Object.class });
}
catch(ClassNotFoundException e) {
return null;
}
catch(NoSuchMethodException e) {
throw new UndeclaredThrowableException(e);
}
}
}