F# Async through Agent= inbox as Queue

Agent are mailbox and can run async block, similar to run a async block inside a function.




open System
open System.Net 
open Microsoft.FSharp.Control.WebExtensions 
open System.Diagnostics 
open System.IO 


let urlList= ["cnn" , "http://www.cnn.com"
              "china", "http://www.china.com"
             ]


let fetch( url :string) = 
        let uri = new Uri(url)
        let c = new WebClient()
        let html =c.DownloadString(uri)
        printfn "%s" html

let fetchAsync(n: string, url :string) = 
    async {
        let uri = new Uri(url)
        let c = new WebClient()
        let! html =c.AsyncDownloadString(uri)
        printfn "%s" html
    }

let runAsync() =
    urlList 
    |> Seq.map fetchAsync
    |> Async.Parallel 
    |> Async.RunSynchronously 

let runSync() = 
    "http://www.cnn.com"
    |> fetch


let s= new StreamWriter("c:\working\1.txt",true)
s.AutoFlush <-true
let agent =
    MailboxProcessor.Start( fun inbox ->
     async {    while true do
                let! msg =inbox.Receive()
               // fetch(msg)
                s.WriteLine(DateTime.Now.ToString()+ " "+msg);
                })


[]
let main arg =
    runSync()
    fetch("http://www.cnn.com")
    
    runAsync() |> ignore
 
    agent.Post("http://www.cnn.com")
    agent.Post("http://www.china.com")
    agent.Post("http://www.goolge.com")
    agent.Post("http://www.fb.com")
    let mutable b=true
    let mutable n=1
    Console.ReadLine() |> ignore
    while b do
        n<-n+1
        if n>1000 then
            b <-false
        agent.Post(n.ToString())

    Console.ReadLine() |> ignore
    s.Close()
    0