Future instead of blocking the current thread.
async in front of
closure, or a
block to turn the marked code into a
As such the code will not be run immediately, but will only be evaluated when the returned
We have written an async book detailing
await and trade-offs compared to using threads.
async is a keyword from the 2018 edition onwards.
It is available for use in stable Rust from version 1.39 onwards.