Stop/Cancel running threads

Question

In my windows service application, I started multiple threads as:

class ConsumingEnumerableDemo
{
   // Demonstrates: 
   //      BlockingCollection<T>.Add() 
   //      BlockingCollection<T>.CompleteAdding() 
   //      BlockingCollection<T>.GetConsumingEnumerable() 
   public static void BC_GetConsumingEnumerable()
   {
       using (BlockingCollection<int> bc = new BlockingCollection<int>())
       {

           // Kick off a producer task
           Task.Factory.StartNew(() =>
           {
               for (int i = 0; i < 10; i++)
               {
                   bc.Add(i);
                   Thread.Sleep(100); // sleep 100 ms between adds
               }

               // Need to do this to keep foreach below from hanging
               bc.CompleteAdding();
           });

           // Now consume the blocking collection with foreach. 
           // Use bc.GetConsumingEnumerable() instead of just bc because the 
           // former will block waiting for completion and the latter will 
           // simply take a snapshot of the current state of the underlying collection. 
           foreach (var item in bc.GetConsumingEnumerable())
           {
               Console.WriteLine(item);
           }
        }
      }
    }

If I want to stop the tasks, how? I heard about "Cancellation Tokens" but not sure how to apply it to the case.

Answer 1

Just define a Cancellation Token Source

var cts = new CancellationTokenSource();

And use it like this:

 Task.Factory.StartNew(() =>
        {
            for (int i = 0; i < 10; i++)
            {
                bc.Add(i);
                Thread.Sleep(100); // sleep 100 ms between adds
                cts.ThrowIfCancellationRequested();
            }

            // Need to do this to keep foreach below from hanging
            bc.CompleteAdding();
        },cts.Token);

When you want to cancel your task, use:

cts.Cancel();

Also you might want take a look at these blog posts:

1. Parallel Programming: Task Cancellation
2. Async in 4.5: Enabling Progress and Cancellation in Async APIs