content: package org.apache.lucene.util.cache;
  
  /**
   * 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.
   */
  
  import java.io.Closeable;
  
  /**
   * Base class for cache implementations.
   */
  public abstract class Cache<K,V> implements Closeable {
    
    /**
     * Simple Cache wrapper that synchronizes all
     * calls that access the cache. 
     */
    static class SynchronizedCache<K,V> extends Cache<K,V> {
      private Object mutex;
      private Cache<K,V> cache;
      
      SynchronizedCache(Cache<K,V> cache) {
        this.cache = cache;
        this.mutex = this;
      }
      
      SynchronizedCache(Cache<K,V> cache, Object mutex) {
        this.cache = cache;
        this.mutex = mutex;
      }
      
      @Override
      public void put(K key, V value) {
        synchronized(mutex) {cache.put(key, value);}
      }
      
      @Override
      public V get(Object key) {
        synchronized(mutex) {return cache.get(key);}
      }
      
      @Override
      public boolean containsKey(Object key) {
        synchronized(mutex) {return cache.containsKey(key);}
      }
      
      @Override
      public void close() {
        synchronized(mutex) {cache.close();}
      }
      
      @Override
      Cache<K,V> getSynchronizedCache() {
        return this;
      }
  
  	@Override
  	public V remove(Object key) {
  	      synchronized(mutex) {return cache.remove(key);}
  
  	}
  
  	@Override
  	public int size() {
  	      synchronized(mutex) {return cache.size();}
  
  	}
    }
    
    /**
     * Returns a thread-safe cache backed by the specified cache. 
     * In order to guarantee thread-safety, all access to the backed cache must
     * be accomplished through the returned cache.
     */
    public static <K,V> Cache<K,V> synchronizedCache(Cache<K,V> cache) {
      return cache.getSynchronizedCache();
    }
  
    /**
     * Called by {@link #synchronizedCache(Cache)}. This method
     * returns a {@link SynchronizedCache} instance that wraps
     * this instance by default and can be overridden to return
     * e. g. subclasses of {@link SynchronizedCache} or this
     * in case this cache is already synchronized.
     */
    Cache<K,V> getSynchronizedCache() {
      return new SynchronizedCache<K,V>(this);
    }
    
    /**
     * Puts a (key, value)-pair into the cache. 
     */
    public abstract void put(K key, V value);
    
    
    public abstract int size();
    
    /**
     * Returns the value for the given key. 
     */
    public abstract V get(Object key);
    
    public abstract V remove(Object key);
    
    /**
     * Returns whether the given key is in this cache. 
     */
    public abstract boolean containsKey(Object key);
    
    /**
     * Closes the cache.
     */
    public abstract void close();
    
  }
  