How many threads to use? How many thread pools or execution contexts do we need? How to minimize overhead for the better performance in async world?

How to propagate errors in async world? What are caveats of using exceptions in async programming? Use exceptions as a primary propagation mechanism while being on a safe side.

How the async code looks like, How to make it more readable and look like non-async code. Extending Future capabilities to match our needs.

Some tricks how to reliably test multithreaded code in Java/Scala...