@Override
    public void shutdown() {
        super.shutdown();
        executorService.shutdownNow();
    }
Shuts down the client, releasing all managed resources. This includes forcibly terminating all pending
asynchronous service calls. Clients who wish to give pending asynchronous service calls time to complete should
call {@code getExecutorService().shutdown()} followed by {@code getExecutorService().awaitTermination()} prior to
calling this method.
aws-java-sdk-mainframemodernization/src/main/java/com/amazonaws/services/mainframemodernization/AWSMainframeModernizationAsyncClient.java