Problems with windows service, blockingcollection, and Multithreading

Question

My scenario:

• Windows Service .NET 4
• I poll a database for entities.
• When new entities come in they are added to a BlockingCollection.
• In the service's OnStart I create a System.Threading.Tasks.Task whose job is to enumerate the BlockingCollection (using GetConsumingEnumerable()).

The problem I'm having is this:

• When an unhandled exception occurs in the task, I want the exception logged and the service stopped.
• I can't catch exceptions from the task unless I call Task.Wait().
• If I call Task.Wait() the OnStart method blocks and the service never finishes starting.

So how can I make this work?

Answer 1

You can handle exceptions in a task using the `.ContinueWith' method:

Task.Factory.StartNew(() => {

    // Do some long action
    Thread.SpinWait(5000000);

    // that eventually has an error :-(
    throw new Exception("Something really bad happened in the task.");

    // I'm not sure how much `TaskCreationOptions.LongRunning` helps, but it sounds 
    // like it makes sense to use it in your situation.
}, TaskCreationOptions.LongRunning).ContinueWith(task => {

    var exception = task.Exception;

    /* Log the exception */

}, TaskContinuationOptions.OnlyOnFaulted); // Only run the continuation if there was an error in the original task.