Asynchronous response from request handlers in aws cloudformation resource type

I am following the below guide to onboard a new resource type to aws cloudformation:

https://docs.aws.amazon.com/cloudformation-cli/latest/userguide/resource-type-walkthrough.html

I am using JAVA to code the CRUD request handlers for the resource type. Looking at the method signature of the auto-generated handlers, it seems like there is no way to return a ProgressEvent wrapped in a Java future from the handlers.

Does this mean that aws does not allow to asynchronously return the ProgressEvent response and the call to the request handler is a blocking call?

The caller code for the java request handlers is present here:

https://github.com/aws-cloudformation/cloudformation-cli-java-plugin/tree/master/src/main/java/software/amazon/cloudformation

The invokeHandler() method in AbstractWrapper.java and handleRequest() method in LambdaWrapper.java seems to always return a synchronous response. Is there no way to return an async response from the request handlers?