Asynchronous function calls in Parallel

Question

Following version is calling all functions synchronously,

I'm looking to find out how to call asynchronous functions in parallel and return all results and errors to the caller.

Request

let requestAsync (url: string) : Async<Result<string, Error>> =
    async {
        Console.WriteLine ("Simulating request " + url)
        try
            do! Async.Sleep(1000)
            return Ok (url + ": body...")
        with :? WebException as e ->
            return Error {code = 500; message = "Internal Server Error";}
    }

Test

[<TestMethod>]
member this.TestrequestAsync() =
    let urls = [|
        "http://www.example.com/1";
        "http://www.example.com/2";
        "http://www.example.com/3";
        "http://www.example.com/4";
        "http://www.example.com/5";
        "http://www.example.com/6";
        "http://www.example.com/7";
        "http://www.example.com/8";
        "http://www.example.com/9";
        "http://www.example.com/10";
    |]

    urls
    |> Array.map (fun url -> requestAsync url |> Async.RunSynchronously) // Async.Parallel some mismatch

    // Iterate results

Ideally to be able to match Ok and Error results while iterating through results

Edit based on the answer.

let result =
    urls
    |> Seq.map Entity.requestDetailAsync2
    |> Async.Parallel
    |> Async.RunSynchronously


result
|> Array.iter Console.WriteLine // match x with Ok and Error?

Attempt

result |> Array.iter (fun data -> match data with
                                      | Ok result -> Console.WriteLine(result)
                                      | Error error -> Console.WriteLine(error) )

Iteration using For in

for r in result do
    match r with
    | Ok re -> Console.WriteLine(re)
    | Error error -> Console.WriteLine(error)

Taylor Wood · Accepted Answer · 2018-03-27 11:04:48Z

2

You can use Async.Parallel to run many async operations in parallel:

let results =
  urls
  |> Seq.map requestAsync   // seq<Async<'T>>
  |> Async.Parallel         // async<T' []>
  |> Async.RunSynchronously // T' []

Here's a very similar example on MSDN.

There may be an issue with your requestAsync function return type, or a missing type definition in your example. Here's what I used to verify the solution:

type RequestError = {
  code : int
  message : string
}

let requestAsync (url: string) =
    async {
        Console.WriteLine ("Simulating request " + url)
        try
            do! Async.Sleep(1000)
            return Ok (url + ": body...")
        with :? WebException as e ->
            return Error {code = 500; message = "Internal Server Error";}
    }

answered Mar 27, 2018 at 11:04

Taylor Wood

16.2k1 gold badge24 silver badges38 bronze badges

Sign up to request clarification or add additional context in comments.

5 Comments

Developer11 Over a year ago

thanks, Can you please add the portion for iteration, see my edit please

Developer11 Over a year ago

so if I were to explain the answer, you created a sequence of requestAsync calls and called all of them in parallel Async.Parallel and waited for them to finish Async.RunSynchronously

Developer11 Over a year ago

please see my attempt, do you agree with my attempt or is there a beautiful elegant solution?

Taylor Wood Over a year ago

@Developer11 your code that iteratively prints the results looks fine to me, though there are other ways to factor it e.g. you might find for .. in .. do reads better.

Developer11 Over a year ago

please check for in edit, is that how what you meant?

Collectives™ on Stack Overflow

Asynchronous function calls in Parallel

1 Answer 1

5 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

5 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related