高效可伸缩的结果缓存

/**
 * 要执行的算法，返回结果v
 */
public interface Computable<A, V> {
	public V comput(final A arg);

}

/**
 * 用于缓存数据
 */
public class Memoizer<A, V> implements Computable<A, V> {

	private final ConcurrentMap<A, Future<V>> cache = new ConcurrentHashMap<A, Future<V>>();

	private final Computable<A, V> c;

	private Memoizer(Computable<A, V> c) {
		this.c = c;
	}

	@Override
	public V comput(final A arg) {
		while (true) {
			Future<V> f = cache.get(arg);
			if (f == null) {
				Callable<V> eval = new Callable<V>() {

					@Override
					public V call() throws Exception {
						return c.comput(arg);
					}
				};
				FutureTask<V> ft = new FutureTask<V>(eval);
				//若没有这个key则put。总是返回oldValue
				f = cache.putIfAbsent(arg, ft);
				if (f == null) {
					f = ft;
					ft.run();
				}

			}
			return null;
		}
	}

}