Question

Is this a good design for a background thread that needs to be run using the Task API in .Net 4? My only concern is if we want to cancel that task how I would do it? I know I can just set ProgramEnding to true but I know there is a CancellationToken in the Task API.

This is just an example sample of code so that one thread will be adding to a collection and another thread will be removing from it. The Task is setup as LongRunning as this needs to be running continuously whilst the program is running

private void RemoveFromBlockingCollection()
{
    while (!ProgramEnding)
    {
       foreach (var x in DataInQueue.GetConsumingEnumerable())
       {
          Console.WriteLine("Task={0}, obj={1}, Thread={2}"
                          , Task.CurrentId, x + " Removed"
                          , Thread.CurrentThread.ManagedThreadId);
       }
    }
}

private void button1_Click(object sender, EventArgs e)
{
   DataInQueue = new BlockingCollection<string>();
   var t9 = Task.Factory.StartNew(RemoveFromBlockingCollection
                                 , TaskCreationOptions.LongRunning);

   for (int i = 0; i < 100; i++)
   {
     DataInQueue.Add(i.ToString());
     Console.WriteLine("Task={0}, obj={1}, Thread={2}", 
                       Task.CurrentId, i + " Added", 
                       Thread.CurrentThread.ManagedThreadId);
     Thread.Sleep(100);
   }
   ProgramEnding = true;
}

UPDATE: I have found that I can remove the ProgramEnding boolean and use DataInQueue.CompleteAdding which which bring the thread to an end.

Answer 1

As you already mentioned, you can use the CancellationToken. Do it this way:

var cancellationTokenSource = new CancellationTokenSource();
Task.Factory.StartNew(RemoveFromBlockingCollection
                      , TaskCreationOptions.LongRunning
                      , cancellationTokenSource.Token);  

And later in your code, you can cancel the task with:

cancellationTokenSource.Cancel();

In your long running task you can ask the token, if cancellation was requested:

if (cancellationTokenSource.Token.IsCancellationRequested)