A very brief example of parallelism in F#.

fsharp_run_tasks_parallelism.fs

open System
open System.IO
open System.Drawing

let ResizeImage(img:Image):Image=
   let siz = new Size(60,60)
   let bmp:Bitmap= new Bitmap(img,siz)
   let img:Image = bmp :> Image
   img

let DestFileName(pref:string,filePath:string):string =
    let ffl = new FileInfo(filePath)
    let nm = pref + ffl.Name
    let newpath = ffl.DirectoryName+"\\"+nm
    newpath

let FetchAsync (file:string)=
     async{
      try
      use stream = File.OpenRead(file)
      let! bytes = stream.AsyncRead(int stream.Length)
      use memstream = new MemoryStream(bytes)
      use image = Image.FromStream(memstream)
      use smallImage = ResizeImage(image)
      let destFileName = DestFileName("_s2_",file)
      smallImage.Save(destFileName )
      with    
        |  (ex:System.Exception) -> 
          printfn "%s" ex.Message
     }
     
let myFunc = 
    let ddr = new DirectoryInfo (@"G:\IMGS\CATALOG")
    let getName = Array.map (fun (x:FileInfo) -> x.FullName)
    let files:string[] = ddr.GetFiles() |> getName
    let tasks = [for file in files -> FetchAsync(file)  ]     
    let parallelTasks = Async.Parallel tasks
    Async.RunSynchronously parallelTasks |> ignore


[<EntryPoint>]
let main argv = 
    myFunc   
    System.Console.ReadKey() |> ignore
    0