// Timed Get
  // There are a few design constraints to consider
  // * We want to be responsive to small timeouts, unpark() has non trivial latency overheads (I
  //   have observed 12 micros on 64-bit linux systems to wake up a parked thread). So if the
  //   timeout is small we shouldn't park(). This needs to be traded off with the cpu overhead of
  //   spinning, so we use SPIN_THRESHOLD_NANOS which is what AbstractQueuedSynchronizer uses for

  // Timed Get
  // There are a few design constraints to consider
  // * We want to be responsive to small timeouts, unpark() has non trivial latency overheads (I
  //   have observed 12 micros on 64-bit linux systems to wake up a parked thread). So if the
  //   timeout is small we shouldn't park(). This needs to be traded off with the cpu overhead of
  //   spinning, so we use SPIN_THRESHOLD_NANOS which is what AbstractQueuedSynchronizer uses for

    @Override
    @CheckForNull
    public E getNext() {
      return null;
    }
  }

  /** Marker interface for {@link InternalEntry} implementations for strong values. */
  interface StrongValueEntry<K, V, E extends InternalEntry<K, V, E>>
      extends InternalEntry<K, V, E> {}

  /** Marker interface for {@link InternalEntry} implementations for weak values. */

    @Override
    @CheckForNull
    public E getNext() {
      return null;
    }
  }

  /** Marker interface for {@link InternalEntry} implementations for strong values. */
  interface StrongValueEntry<K, V, E extends InternalEntry<K, V, E>>
      extends InternalEntry<K, V, E> {}

  /** Marker interface for {@link InternalEntry} implementations for weak values. */

                final AtomicInteger parked = new AtomicInteger();

                @Override
                public <T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks)
                        throws InterruptedException {
                    setCorePoolSize(parallelism + parked.incrementAndGet());
                    try {

   * value, you should always choose it explicitly.
   *
   * <p>The current implementation uses the concurrency level to create a fixed number of hashtable
   * segments, each governed by its own write lock. The segment lock is taken once for each explicit
   * write, and twice for each cache loading computation (once prior to loading the new value, and
   * once after loading completes). Much internal cache management is performed at the segment