camundafeel.de.odysseus.el.tree.impl.Cache Maven / Gradle / Ivy
/*
* Copyright 2006-2009 Odysseus Software GmbH
*
* 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 de.odysseus.el.tree.impl;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentLinkedQueue;
import java.util.concurrent.ConcurrentMap;
import java.util.concurrent.atomic.AtomicInteger;
import de.odysseus.el.tree.Tree;
import de.odysseus.el.tree.TreeCache;
/**
* Concurrent (thread-safe) FIFO tree cache (using classes from
* java.util.concurrent). After the cache size reached a certain
* limit, some least recently used entry are removed, when adding a new entry.
*
* @author Christoph Beck
*/
public final class Cache implements TreeCache {
private final ConcurrentMap map;
private final ConcurrentLinkedQueue queue;
private final AtomicInteger size;
private final int capacity;
/**
* Creates a new cache with the specified capacity
* and default concurrency level (16).
*
* @param capacity
* Cache size. The actual size may exceed it temporarily.
*/
public Cache(int capacity) {
this(capacity, 16);
}
/**
* Creates a new cache with the specified capacity and concurrency level.
*
* @param capacity
* Cache size. The actual map size may exceed it temporarily.
* @param concurrencyLevel
* The estimated number of concurrently updating threads. The
* implementation performs internal sizing to try to accommodate
* this many threads.
*/
public Cache(int capacity, int concurrencyLevel) {
this.map = new ConcurrentHashMap(16, 0.75f, concurrencyLevel);
this.queue = new ConcurrentLinkedQueue();
this.size = new AtomicInteger();
this.capacity = capacity;
}
public int size() {
return size.get();
}
public Tree get(String expression) {
return map.get(expression);
}
public void put(String expression, Tree tree) {
if (map.putIfAbsent(expression, tree) == null) {
queue.offer(expression);
if (size.incrementAndGet() > capacity) {
size.decrementAndGet();
map.remove(queue.poll());
}
}
}
}