[carllerche]

Tokio author here. Generally speaking, I recommend strongly against using FuturesUnordered unless you know all the pitfalls. We are working on an alternative utility that should hopefully avoid the issues described here and others: https://github.com/tokio-rs/tokio/pull/4335

[psarna]

That's great news! Especially that the observed performance of the test program based on FuturesUnordered, even though it stopped being quadratic, it was still considerably slower than the task::unconstrained one, which suggests there's room for improvement. Probably due to the fact that you still pay with a constant number of polls (32) each time you go out of budget.

[carllerche]

IMO FuturesUnordered should stop executing futures when it sees a "yield". An explicit yield signals control should be returned to the runtime. FuturesUnordered does not respect this.