Moxa

import java.util.concurrent.Callable;
import java.util.concurrent.CancellationException;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.Future;
import java.util.concurrent.FutureTask;

public class MyCache<K, V> implements Computable<K, V> {

    private final ConcurrentHashMap<K, Future<V>> cache = new ConcurrentHashMap<K, Future<V>>();
    private final Computable<K, V> c;

    public MyCache(Computable<K, V> c) {
        this.c = c;
    }

    @Override
    public V compute(final K key) throws InterruptedException {
        while (true) {
            Future<V> f = cache.get(key);
            if (f == null) {
                Callable<V> eval = new Callable<V>() {

                    @Override
                    public V call() throws Exception {
                        return c.compute(key);
                    }
                };
                FutureTask<V> ft = new FutureTask<V>(eval);
                f = cache.putIfAbsent(key, ft);
                if (f == null) {
                    f = ft;
                    ft.run();
                }
            }
            try {
                return f.get();
            } catch (CancellationException e) {
                cache.remove(key, f);
            } catch (ExecutionException e) {
                throw new RuntimeException(e.getCause());
            }
        }
    }

    public static interface Computable<K, V> {

        public V compute(K k) throws InterruptedException;
    }
}