{"id":940,"date":"2009-12-21T18:01:33","date_gmt":"2009-12-21T17:01:33","guid":{"rendered":"http:\/\/www.navision-blog.de\/2009\/12\/21\/observing-asynchronous-downloads-with-f-and-the-reactive-extensions-for-net\/"},"modified":"2022-11-19T13:02:38","modified_gmt":"2022-11-19T13:02:38","slug":"observing-asynchronous-downloads-with-f-and-the-reactive-extensions-for-net","status":"publish","type":"post","link":"http:\/\/www.navision-blog.de\/blog\/2009\/12\/21\/observing-asynchronous-downloads-with-f-and-the-reactive-extensions-for-net\/","title":{"rendered":"Observing asynchronous downloads with F# and the Reactive Extensions for .NET"},"content":{"rendered":"

In one of my lasts posts I showed how we can transform some of the operators from the Reactive Framework for an easier use in F#<\/a>. This time I will demonstrate how we can use this API and asynchronous workflows to download a couple of websites asynchronous and in parallel.<\/p>\n

First of all we create a synchronous download function:<\/p>\n

\n

let<\/span> SyncHttp (url:string) =<\/p>\n

  let<\/span> request = WebRequest.Create url<\/p>\n

  let<\/span> response = request.GetResponse()<\/p>\n

  use<\/span> stream = response.GetResponseStream()<\/p>\n

  use<\/span> reader = new<\/span> StreamReader(stream)<\/p>\n

  let<\/span> result = reader.ReadToEnd()<\/p>\n

  url,result<\/p>\n<\/p>\n<\/div>\n

In F# we can easily make this function asynchronously:<\/p>\n

\n

let<\/span> AsyncHttp (url:string) =<\/p>\n

  async { \/\/ using asynchronous workflows<\/span><\/p>\n

    let<\/span> request = WebRequest.Create url<\/p>\n

    \/\/ async call of GetResponse<\/span><\/p>\n

    let!<\/span> response = request.AsyncGetResponse()<\/p>\n

    use<\/span> stream = response.GetResponseStream()<\/p>\n

    use<\/span> reader = new<\/span> StreamReader(stream)<\/p>\n

    \/\/ async call of ReadToEnd<\/span><\/p>\n

    let!<\/span> result = reader.AsyncReadToEnd()<\/p>\n

    return<\/span> url,result}  <\/p>\n<\/p>\n<\/div>\n

Now we use this AsyncHttp function to create a list of async downloads:<\/p>\n

\n

\/\/\/ Async<string * string> list<\/span><\/p>\n

let<\/span> downloads =<\/p>\n

  ["http:\/\/www.google.com"<\/span>;<\/p>\n

   "http:\/\/www.twitter.com"<\/span>;<\/p>\n

   "http:\/\/www.nytimes.com\/"<\/span>;<\/p>\n

   "http:\/\/www.navision-blog.de\/"<\/span>;<\/p>\n

   "http:\/\/www.nba.com\/"<\/span>]  <\/p>\n

    |> List.map AsyncHttp<\/p>\n<\/p>\n<\/div>\n

The next step is to convert the list of async calls into a list of observables and to merge this list into a single IObservable. The effect is that whenever one download is completed we will be notified about the result:<\/p>\n

\n

\/\/\/ IObservable<string * string><\/span><\/p>\n

let<\/span> observableDownloads =<\/p>\n

  downloads<\/p>\n

    |> Seq.map Observable.ofAsync<\/p>\n

    |> Observable.merge<\/p>\n

 <\/p>\n

 <\/p>\n<\/p>\n<\/div>\n

\n

observableDownloads<\/p>\n

  |> Observable.subscribe (fun<\/span> (url,result) -><\/span><\/p>\n

       printfn "%A: %d"<\/span> url result.Length)<\/p>\n

 <\/p>\n<\/p>\n<\/div>\n

If you want to learn more about Observable.merge and see the marble diagram<\/a> you should watch this video<\/a>.<\/p>\n

https:\/\/hrvatskaedfarmacija.com<\/a><\/div>\n","protected":false},"excerpt":{"rendered":"

In one of my lasts posts I showed how we can transform some of the operators from the Reactive Framework for an easier use in F#. This time I will demonstrate how we can use this API and asynchronous workflows to download a couple of websites asynchronous and in parallel. First of all we create […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":[],"categories":[448],"tags":[664,579,578],"_links":{"self":[{"href":"http:\/\/www.navision-blog.de\/blog\/wp-json\/wp\/v2\/posts\/940"}],"collection":[{"href":"http:\/\/www.navision-blog.de\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/www.navision-blog.de\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/www.navision-blog.de\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"http:\/\/www.navision-blog.de\/blog\/wp-json\/wp\/v2\/comments?post=940"}],"version-history":[{"count":3,"href":"http:\/\/www.navision-blog.de\/blog\/wp-json\/wp\/v2\/posts\/940\/revisions"}],"predecessor-version":[{"id":2015,"href":"http:\/\/www.navision-blog.de\/blog\/wp-json\/wp\/v2\/posts\/940\/revisions\/2015"}],"wp:attachment":[{"href":"http:\/\/www.navision-blog.de\/blog\/wp-json\/wp\/v2\/media?parent=940"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/www.navision-blog.de\/blog\/wp-json\/wp\/v2\/categories?post=940"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/www.navision-blog.de\/blog\/wp-json\/wp\/v2\/tags?post=940"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}