* Handler for exceptions thrown by event subscribers.
 *
 * @since 16.0
 */
@ElementTypesAreNonnullByDefault
public interface SubscriberExceptionHandler {
  /** Handles exceptions thrown by subscribers. */
  void handleException(Throwable exception, SubscriberExceptionContext context);

       *
       * Fortunately, exceptions rarely contain references to expensive resources.
       */

      //
      seenExceptionsLocal = newConcurrentHashSet();
      /*
       * Other handleException() callers may see this as soon as we publish it. We need to populate
       * it with the initial failure before we do, or else they may think that the initial failure
       * has never been seen before.
       */