并行计算不会产生结果？

Question

我的代码似乎在我的异步工作流程的最后一次迭代后冻结了。它是代码中的一个错误，还是只需要花费很长时间（20分钟加）来完成工作流程？

let rec list_primes x y = 
//returns an array with all primes between x and y
if x < y then
    if is_prime x (x |> sqrt |> floor) then 
        printfn "%A" x
        x :: list_primes (x + 1.0) y
    else 
        let n_x = x |> next_prime
        n_x :: list_primes (n_x + 1.0) y   
else 
    []

let filt (x:float) = 
    if x < 10000.0 then 
        true
    else 
        false 

let list_of_primes = List.filter (filt) (list_primes 1000.0 10000.0)

let iter =  [0..((List.length list_of_primes)-3)]

let equal_difference (list:List<float>) iter =
printfn "%A" iter
async{
let mutable a = [|[||]|]
for x in (iter + 1)..(list.Length - 1) do
    printfn "inside loop, x = %A" x 
    let temp = test_sum_in_list list.[x] list.[iter] list
    //let temp1 = test_sum_in_list (list.[x] + list.[iter]) list.[x] list
    if temp then
        a <- Array.append a [|[|list.[x]; list.[iter]; (list.[x] + list.[iter]);|]|]
        printf "added %A" a
let result = a
return result 
}

let result = iter
            |> List.map (equal_difference list_of_primes)
            |> Async.Parallel
            |> Async.RunSynchronously