code: public void shutdownNow(boolean shutDownS3Client) {
          if (shutDownThreadPools) {
              executorService.shutdownNow();
              timedThreadPool.shutdownNow();
          }
  
          if (shutDownS3Client) {
              s3.shutdown();
          }
      }
docs: Forcefully shuts down this TransferManager instance - currently executing
  transfers will not be allowed to finish. Callers should use this method
  when they either:
  <ul>
  <li>have already verified that their transfers have completed by checking
  each transfer's state
  <li>need to exit quickly and don't mind stopping transfers before they
  complete.
  </ul>
  <p>
  Callers should also remember that uploaded parts from an interrupted
  upload may not always be automatically cleaned up, but callers can use
  {@link #abortMultipartUploads(String, Date)} to clean up any upload
  parts.
  
  @param shutDownS3Client
  Whether to shut down the underlying Amazon S3 client.