// TODO(cpovirk): Annotate for nullness.
class LocalCache<K, V> extends AbstractMap<K, V> implements ConcurrentMap<K, V> {

  /*
   * The basic strategy is to subdivide the table among Segments, each of which itself is a
   * concurrently readable hash table. The map supports non-blocking reads and concurrent writes
   * across different segments.
   *

   *     the {@link ExecutionException} thrown by {@link Future#get()} on the {@link Future}
   *     underlying this step or, if {@code get()} throws a different kind of exception, that
   *     exception itself. To avoid hiding bugs and other unrecoverable errors, callers should
   *     prefer more specific types, avoiding {@code Throwable.class} in particular.

// TODO(cpovirk): Annotate for nullness.
class LocalCache<K, V> extends AbstractMap<K, V> implements ConcurrentMap<K, V> {

  /*
   * The basic strategy is to subdivide the table among Segments, each of which itself is a
   * concurrently readable hash table. The map supports non-blocking reads and concurrent writes
   * across different segments.
   *

  }

  /** An implementation of {@link Map#putAll}. */
  static <K extends @Nullable Object, V extends @Nullable Object> void putAllImpl(
      Map<K, V> self, Map<? extends K, ? extends V> map) {
    for (Entry<? extends K, ? extends V> entry : map.entrySet()) {
      self.put(entry.getKey(), entry.getValue());
    }
  }

  static class KeySet<K extends @Nullable Object, V extends @Nullable Object>