Question

I’m trying to do some async stuff in a webservice method. Let say I have the following API call: http://www.example.com/api.asmx

and the method is called GetProducts().

I this GetProducts methods, I do some stuff (eg. get data from database) then just before i return the result, I want to do some async stuff (eg. send me an email).

So this is what I did.

[WebMethod(Description = 'Bal blah blah.')] public IList<Product> GetProducts() {     // Blah blah blah ..     // Get data from DB .. hi DB!     // var myData = .......     // Moar clbuttic blahs :)  (yes, google for clbuttic if you don't know what that is)      // Ok .. now send me an email for no particular reason, but to prove that async stuff works.     var myObject = new MyObject();     myObject.SendDataAsync();      // Ok, now return the result.     return myData;     } }  public class TrackingCode {     public void SendDataAsync()     {         var backgroundWorker = new BackgroundWorker();         backgroundWorker.DoWork += BackgroundWorker_DoWork;         backgroundWorker.RunWorkerAsync();         //System.Threading.Thread.Sleep(1000 * 20);     }      private void BackgroundWorker_DoWork(object sender, DoWorkEventArgs e)     {         SendEmail();     } } 

Now, when I run this code the email is never sent. If I uncomment out the Thread.Sleep .. then the email is sent.

So … why is it that the background worker thread is torn down? is it dependant on the parent thread? Is this the wrong way I should be doing background or forked threading, in asp.net web apps?

Answer 1

BackgroundWorker is useful when you need to synchronize back to (for example) a UI* thread, eg for affinity reasons. In this case, it would seem that simply using ThreadPool would be more than adequate (and much simpler). If you have high volumes, then a producer/consumer queue may allow better throttling (so you don’t drown in threads) – but I suspect ThreadPool will be fine here…

public void SendDataAsync() {     ThreadPool.QueueUserWorkItem(delegate     {         SendEmail();     }); } 

Also – I’m not quite sure what you want to achieve by sleeping? This will just tie up a thread (not using CPU, but doing no good either). Care to elaborate? It looks like you are pausing your actual web page (i.e. the Sleep happens on the web-page thread, not the e-mail thread). What are you trying to do here?

*=actually, it will use whatever sync-context is in place