[obstinate]

If I compare the three alternatives:

    - Standard blocking code in OS threads.
    - Future-based code.
    - Coroutines with explicit annotation.

The latter is probably only viable for very large organizations in terms of engineering cost. The other two are doable for smaller organizations.

[pron]

Can you explain why? Futures seem to be much more intrusive than the other two.

[obstinate]

They are intrusive in the sense that the code looks much different. On the other hand, I'd guess they are less error prone. Marking up syscalls would be a constant cognitive load, since you have to remember to do it each time (or else maintain an abstraction layer). But once you've decided to use futures, that's just how you do async.