freemarker.cache.SoftCacheStorage Maven / Gradle / Ivy
/*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you 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 java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;
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 parameterless constructor uses a thread-safe map
* since 2.3.24 or Java 5.
*
* @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;
/**
* Creates an instance that uses a {@link ConcurrentMap} internally.
*/
public SoftCacheStorage() {
this(new ConcurrentHashMap());
}
/**
* Returns true if the underlying Map is a {@code ConcurrentMap}.
*/
public boolean isConcurrent() {
return concurrent;
}
public SoftCacheStorage(Map backingMap) {
map = backingMap;
this.concurrent = map instanceof ConcurrentMap;
}
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);
}
}
}