async_trait is easy to use, but note that it’s using heap allocations to achieve this. This heap allocation has performance overhead.

The challenges in language support for async trait are deep Rust and probably not worth describing in-depth. Niko Matsakis did a good job of explaining them in this post if you are interested in digging deeper.

Try creating a new sleeper struct that will sleep for a random amount of time and adding it to the Vec.