Futures-rs: Shall quadratic complexity of `join_all` be documented?

[vi]

• https://github.com/tokio-rs/tokio/issues/2401
• https://users.rust-lang.org/t/hyper-tonic-client-performance/47253/2

[Nemo157]

Maybe even a

#[cfg(debug_assertions)]
if futures.len() > 1000 {
  warn!("join_all is only intended for running small dynamic lists of futures, use FuturesUnordered for large numbers");
}

(probably could even be a much lower limit, I don't know if anyone has ever tested what a good limit is).

[vi]

Does futures really use log?

[Nemo157]

Not currently, but the only other option I can think of would be debug_assert! which seems far too drastic to me.

[taiki-e]

(I think the fundamental solution is to change the name to include a word that describes its feature(=only efficient for relatively small lists), but that's a breaking change of course.)

[Darksonn]

Another option would be to have it use FuturesUnordered internally when the number of futures is large.