code: @Override
    public ManagedChannelImpl shutdownNow() {
      channelLogger.log(ChannelLogLevel.DEBUG, "shutdownNow() called");
      shutdown();
      uncommittedRetriableStreamsRegistry.onShutdownNow(SHUTDOWN_NOW_STATUS);
      final class ShutdownNow implements Runnable {
        @Override
        public void run() {
          if (shutdownNowed) {
            return;
          }
          shutdownNowed = true;
          maybeShutdownNowSubchannels();
        }
      }
  
      syncContext.execute(new ShutdownNow());
      return this;
    }
docs: Initiates a forceful shutdown in which preexisting and new calls are cancelled. Although
  forceful, the shutdown process is still not instantaneous; {@link #isTerminated()} will likely
  return {@code false} immediately after this method returns.