e);
      }
    }

    private static final class RunnableExecutorPair {
      final Runnable runnable;
      final Executor executor;
      @Nullable RunnableExecutorPair next;

      RunnableExecutorPair(Runnable runnable, Executor executor, RunnableExecutorPair next) {
        this.runnable = runnable;
        this.executor = executor;
        this.next = next;
      }