Question

I have an IIS hosted WCF webservice.

It has a method on it (let’s call it “ConfirmOrder”). When this method is called, I want to
1. Do some quick stuff to the database, resulting in an OrderId
2. Start a new thread that will do some slow work (e.g. generate an email and send it)
3. Return the OrderId from 1. synchronously to the client.
4. Eventually, when it’s finished, the new thread created in 2. will have done all the rest of the processing and sent the email.

Questions:

(1) I did have code like:

// do printing and other tasks 
OrderConfirmedThreadHelper helper = new OrderConfirmedThreadHelper(userSession, result);
// some things first (like generating barcodes) in this thread 
Logger.Write(basket.SessionId, String.Format("Before ConfirmOrderSync"), LogCategoryEnum.Sales, System.Diagnostics.TraceEventType.Verbose);
helper.ConfirmOrderSync();
Logger.Write(basket.SessionId, String.Format("After ConfirmOrderSync"), LogCategoryEnum.Sales, System.Diagnostics.TraceEventType.Verbose);
// slower things (like rendering, sending email) in a separate thread
Thread helperThread = new Thread(new ThreadStart(helper.ConfirmOrderAsync));
helperThread.Start();
return result;

but it seemed to cause problems; at least, the service kept locking up. Is this a bad thing to do?

(2) I tried changing it to

// slower things (like rendering, sending email) in a separate thread            
ThreadPool.QueueUserWorkItem(new WaitCallback(helper.ConfirmOrderAsync));

but the ThreadPool thread seems to be being killed as soon as the main thread has finished, because it’s a Background thread.

Is there a better way of doing this – short of writing a whole new windows service to communicate with?

Answer 1

If the second thead finishes after the request thread (the one that comes from the browser) you’re in problems, since it’ll get reclaimed by the runtime and terminated.
If you can afford to wait (if it’s only going to send an email i’ll be a couple of seconds) you can use ManualResetEvent to synchronize one thread to wait for the other to finish and clean up gracefully.

If you can’t wait, well the best choice in this case for the mail process is one of the following

1. A Windows Service.
2. An .ashx you can call from your client code with a jquery ajax call passing the necessary data to send the mail.
3. A batch job (a scheduled task, a sql server job, etc) that reads pending mails to be sent from the DB and sends them. It would run every X minutes, so you wouldn’t have to worry

Hope that helps!