package org.apache.commons.ognl.internal;
   
   /*
    * 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.
   */
  
  /*
   * $Id: ReentrantReadWriteLockCache.java 1194954 2011-10-29 18:00:27Z mcucchiara $
   */
  
  import org.apache.commons.ognl.internal.entry.CacheEntryFactory;
  
  import java.util.HashMap;
  import java.util.Map;
  import java.util.concurrent.locks.Lock;
  import java.util.concurrent.locks.ReadWriteLock;
  import java.util.concurrent.locks.ReentrantReadWriteLock;
  
  public class ReentrantReadWriteLockCache<K, V>
      implements Cache<K, V>
  {
      private final ReadWriteLock lock = new ReentrantReadWriteLock();
  
      private final Lock readLock = lock.readLock();
  
      private final Lock writeLock = lock.writeLock();
  
      final Map<K, V> cache = new HashMap<K, V>();
  
      private CacheEntryFactory<K, V> cacheEntryFactory;
  
      public ReentrantReadWriteLockCache()
      {
      }
  
      public ReentrantReadWriteLockCache( CacheEntryFactory<K, V> cacheEntryFactory )
      {
          this.cacheEntryFactory = cacheEntryFactory;
      }
  
      public void clear()
      {
          synchronized ( cache )
          {
              cache.clear();
          }
      }
  
      public int getSize()
      {
          synchronized ( cache )
          {
              return cache.size();
          }
      }
  
  
      public V get( K key )
          throws CacheException
      {
          V v;
          boolean shouldCreate;
          readLock.lock();
          try
          {
              v = cache.get( key );
              shouldCreate = shouldCreate( cacheEntryFactory, v );
          }
          finally
          {
              readLock.unlock();
          }
          if ( shouldCreate )
          {
              try
              {
                  writeLock.lock();
                  v = cache.get( key );
                  if ( !shouldCreate( cacheEntryFactory, v ) )
                  {
                      return v;
                  }
                  v = cacheEntryFactory.create( key );
                  cache.put( key, v );
                 return v;
             }
             finally
             {
                 writeLock.unlock();
             }
 
         }
 
         return v;
     }
 
     protected boolean shouldCreate( CacheEntryFactory<K, V> cacheEntryFactory, V v )
         throws CacheException
     {
         if ( cacheEntryFactory != null )
         {
             if ( v == null )
             {
                 return true;
             }
         }
         return false;
     }
 
     public V put( K key, V value )
     {
         writeLock.lock();
         try
         {
             cache.put( key, value );
             return value;
         }
         finally
         {
             writeLock.unlock();
         }
     }
 }