* immutable snapshot of all current subscribers to an event without any locking.
   */
  private final ConcurrentMap<Class<?>, CopyOnWriteArraySet<Subscriber>> subscribers =
      Maps.newConcurrentMap();

  /** The event bus this registry belongs to. */
  @Weak private final EventBus bus;

  SubscriberRegistry(EventBus bus) {
    this.bus = checkNotNull(bus);
  }

  }

  @Empty
  static <K, V> ConcurrentMap<K, V> generateConcurrentMap() {
    return Maps.newConcurrentMap();
  }

  @Generates
  static <K, V> ConcurrentMap<K, V> generateConcurrentMap(K key, V value) {
    ConcurrentMap<K, V> map = Maps.newConcurrentMap();
    map.put(key, value);
    return map;
  }

  @Generates

  }

  public void testConcurrentMap() {
    assertFreshInstance(new TypeToken<ConcurrentMap<String, ?>>() {});
    assertCanGenerateOnly(
        new TypeToken<ConcurrentMap<EmptyEnum, String>>() {}, Maps.newConcurrentMap());
  }

  public void testMultimap() {
    assertFreshInstance(new TypeToken<Multimap<String, ?>>() {});
  }

  public void testHashMultimap() {

  }

  @Empty
  static <K, V> ConcurrentMap<K, V> generateConcurrentMap() {
    return Maps.newConcurrentMap();
  }

  @Generates
  static <K, V> ConcurrentMap<K, V> generateConcurrentMap(K key, V value) {
    ConcurrentMap<K, V> map = Maps.newConcurrentMap();
    map.put(key, value);
    return map;
  }

  @Generates

   * default implementations and are "new"d upon get().
   */
  private static final ConcurrentMap<Class<?>, Class<?>> implementations = Maps.newConcurrentMap();

  private static <T> void setImplementation(Class<T> type, Class<? extends T> implementation) {
    checkArgument(type != implementation, "Don't register %s to itself!", type);
    checkArgument(

  }

  public void testConcurrentMap() {
    assertFreshInstance(new TypeToken<ConcurrentMap<String, ?>>() {});
    assertCanGenerateOnly(
        new TypeToken<ConcurrentMap<EmptyEnum, String>>() {}, Maps.newConcurrentMap());
  }

  public void testMultimap() {
    assertFreshInstance(new TypeToken<Multimap<String, ?>>() {});
  }

  public void testHashMultimap() {

   * default implementations and are "new"d upon get().
   */
  private static final ConcurrentMap<Class<?>, Class<?>> implementations = Maps.newConcurrentMap();

  private static <T> void setImplementation(Class<T> type, Class<? extends T> implementation) {
    checkArgument(type != implementation, "Don't register %s to itself!", type);
    checkArgument(

          builder.add(method);
        }
      }
      return builder.build();
    }

    final Iterable<Method> getInstanceMethods(Class<?> cls) {
      ConcurrentMap<Signature, Method> map = Maps.newConcurrentMap();
      for (Method method : getVisibleMethods(cls)) {
        if (!Invokable.from(method).isStatic()) {
          map.putIfAbsent(new Signature(method), method);
        }
      }
      return map.values();

          builder.add(method);
        }
      }
      return builder.build();
    }

    final Iterable<Method> getInstanceMethods(Class<?> cls) {
      ConcurrentMap<Signature, Method> map = Maps.newConcurrentMap();
      for (Method method : getVisibleMethods(cls)) {
        if (!Invokable.from(method).isStatic()) {
          map.putIfAbsent(new Signature(method), method);
        }
      }
      return map.values();

    return new LinkedHashMap<>(capacity(expectedSize));
  }

  /**
   * Creates a new empty {@link ConcurrentHashMap} instance.
   *
   * @since 3.0
   */
  public static <K, V> ConcurrentMap<K, V> newConcurrentMap() {
    return new ConcurrentHashMap<>();
  }

  /**
   * Creates a <i>mutable</i>, empty {@code TreeMap} instance using the natural ordering of its
   * elements.
   *