Async cache fix in multi-thread-environment for GitHub downloads

[Thorium]

No comments.

[Thorium]

Hehe... first some solution and then more optimized. The last one looks quite nice and the unit test proofs it's working while the normal F# Async won't serialize "correctly".

let internal memoizeAsync f =
    let cache = System.Collections.Concurrent.ConcurrentDictionary<'a, System.Threading.Tasks.Task<'b>>()
    fun x -> // task.Result serialization to sync after done.
        cache.GetOrAdd(x, fun x -> f(x) |> Async.StartAsTask) |> Async.AwaitTask

[forki]

thanks!