org.apache.commons.jexl3.internal.SoftCache Maven / Gradle / Ivy
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/*
* 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 org.apache.commons.jexl3.internal;
import java.lang.ref.SoftReference;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.Map;
import java.util.Set;
import java.util.concurrent.locks.ReadWriteLock;
import java.util.concurrent.locks.ReentrantReadWriteLock;
/**
* A soft referenced cache.
*
* The actual cache is held through a soft reference, allowing it to be GCed
* under memory pressure.
*
* @param the cache key entry type
* @param the cache key value type
*/
public class SoftCache {
/**
* The default cache load factor.
*/
private static final float LOAD_FACTOR = 0.75f;
/**
* The cache size.
*/
private final int size;
/**
* The soft reference to the cache map.
*/
private SoftReference> ref = null;
/**
* The cache r/w lock.
*/
private final ReadWriteLock lock;
/**
* Creates a new instance of a soft cache.
*
* @param theSize the cache size
*/
SoftCache(int theSize) {
size = theSize;
lock = new ReentrantReadWriteLock();
}
/**
* Returns the cache size.
*
* @return the cache size
*/
public int size() {
return size;
}
/**
* Clears the cache.
*/
public void clear() {
lock.writeLock().lock();
try {
ref = null;
} finally {
lock.writeLock().unlock();
}
}
/**
* Gets a value from cache.
*
* @param key the cache entry key
* @return the cache entry value
*/
public V get(K key) {
lock.readLock().lock();
try {
final Map map = ref != null ? ref.get() : null;
return map != null ? map.get(key) : null;
} finally {
lock.readLock().unlock();
}
}
/**
* Puts a value in cache.
*
* @param key the cache entry key
* @param script the cache entry value
*/
public void put(K key, V script) {
lock.writeLock().lock();
try {
Map map = ref != null ? ref.get() : null;
if (map == null) {
map = createCache(size);
ref = new SoftReference>(map);
}
map.put(key, script);
} finally {
lock.writeLock().unlock();
}
}
/**
* Produces the cache entry set.
*
* For testing only, perform deep copy of cache entries
*
* @return the cache entry list
*/
public List> entries() {
lock.readLock().lock();
try {
Map map = ref != null ? ref.get() : null;
if (map == null) {
return Collections.emptyList();
}
final Set> set = map.entrySet();
final List> entries = new ArrayList>(set.size());
for (Map.Entry e : set) {
entries.add(new SoftCacheEntry(e));
}
return entries;
} finally {
lock.readLock().unlock();
}
}
/**
* Creates the cache store.
*
* @param the key type
* @param the value type
* @param cacheSize the cache size, must be > 0
* @return a Map usable as a cache bounded to the given size
*/
public Map createCache(final int cacheSize) {
return new java.util.LinkedHashMap(cacheSize, LOAD_FACTOR, true) {
/**
* Serial version UID.
*/
private static final long serialVersionUID = 1L;
@Override
protected boolean removeEldestEntry(Map.Entry eldest) {
return size() > cacheSize;
}
};
}
}
/**
* A soft cache entry.
*
* @param key type
* @param value type
*/
class SoftCacheEntry implements Map.Entry {
/**
* The entry key.
*/
private final K key;
/**
* The entry value.
*/
private final V value;
/**
* Creates an entry clone.
*
* @param e the entry to clone
*/
SoftCacheEntry(Map.Entry e) {
key = e.getKey();
value = e.getValue();
}
@Override
public K getKey() {
return key;
}
@Override
public V getValue() {
return value;
}
@Override
public V setValue(V v) {
throw new UnsupportedOperationException("Not supported.");
}
}