Testing evaluation strategies for long operations

gistfile1.fs

open System
open System.Threading
open System.Linq
open System.Threading.Tasks
open System.Diagnostics

[<EntryPoint>]
let main argv = 
    let rand = new Random()
    let opCount = 5
    let opAvgMillis = 250.0
    
    let getLengthyOperation () =
        let waitMillis = [1 .. 12]
                         |> Seq.averageBy (fun _ -> rand.NextDouble())
                         |> (*) (opAvgMillis * 2.0)
                         |> int
        fun () -> Thread.Sleep waitMillis; true

    let lengthyOperations = [1 .. opCount]
                            |> Seq.map (fun _ -> getLengthyOperation ())
                            |> Seq.toArray

    let evalStartNew (xs : seq<unit -> bool>) =
        let tasks = xs.Select(fun x -> Task.Factory.StartNew(fun () -> x ())).ToArray()
        Task.WaitAll (tasks |> Seq.map (fun t -> t :> Task) |> Seq.toArray)
        tasks.All (fun t -> t.Result)

    let evalAsParallelDef (xs : seq<unit -> bool>) =
        xs.AsParallel().All(fun f -> f())

    let evalAsParallelForce (n : int) (xs : seq<unit -> bool>) =
        xs.AsParallel().WithDegreeOfParallelism(Math.Min(63, (Math.Max(1, n)))).WithExecutionMode(ParallelExecutionMode.ForceParallelism).All(fun f -> f())
    
    let evals = [(evalStartNew, "evalStartNew"); (evalAsParallelDef, "evalAsParallelDef"); (evalAsParallelForce 2, "evalAsParallelForce 2");
                 (evalAsParallelForce 8, "evalAsParallelForce 8"); (evalAsParallelForce 64, "evalAsParallelForce 64")]
    for (eval, name) in evals do
        let watch = Stopwatch.StartNew ()
        let result = eval lengthyOperations
        watch.Stop ()
        printfn "%s took %A; speedup was x%.3f" name watch.Elapsed (opAvgMillis * (double)opCount / watch.Elapsed.TotalMilliseconds)
    System.Console.ReadLine () |> ignore
    0