Improve the implementation of JoinAll?

[najamelan]

Recently some thought has gone into futures that eternally return Ready and thus never yield to the executor (#2047, #2053, #2130). Particularly concerned are combinators and collections. FuturesUnordered has already been updated to yield every so often.

JoinHandle is another collection that might never yield. Should we implement it with FuturesUnordered under the hood or should we add some counter to the implementation?

[Nemo157]

Using FuturesUnordered under the hood would make JoinAll itself pretty pointless, the only advantage it has over using FuturesUnordered is potentially lower overhead when used for a low number of futures (though I don't know if this has ever been benchmarked).

Unlike FuturesUnordered and Shared, JoinAll doesn't intercept the Waker, so it will not encounter the same issue of never yielding. It will poll each sub-future at most once per poll.

[najamelan]

Looking at the code again, you are right. So I'll close this.