content: /*
   * Copyright 2010-2025 Hyland Software, Inc. and its affiliates.
   *
   * 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 org.activiti.core.el.juel.tree.impl;
  
  import java.util.concurrent.ConcurrentHashMap;
  import java.util.concurrent.ConcurrentLinkedQueue;
  import java.util.concurrent.ConcurrentMap;
  import java.util.concurrent.atomic.AtomicInteger;
  import org.activiti.core.el.juel.tree.Tree;
  import org.activiti.core.el.juel.tree.TreeCache;
  
  /**
   * Concurrent (thread-safe) FIFO tree cache (using classes from
   * <code>java.util.concurrent</code>). 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<String, Tree> map;
      private final ConcurrentLinkedQueue<String> 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<String, Tree>(16, 0.75f, concurrencyLevel);
          this.queue = new ConcurrentLinkedQueue<String>();
          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());
              }
          }
      }
  }
  