public void shutdownNow(boolean shutDownS3Client) {
        if (shutDownThreadPools) {
            executorService.shutdownNow();
            timedThreadPool.shutdownNow();
        }

        if (shutDownS3Client) {
            s3.shutdown();
        }
    }
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.
aws-java-sdk-s3/src/main/java/com/amazonaws/services/s3/transfer/TransferManager.java