Continuation tasks

Given following

Code:

---

static void Main(string[] args)
{
  try
  {
      CancellationTokenSource cts = new CancellationTokenSource();
      Task t = Task.Factory.StartNew(() => MyCanceledMethod(cts.Token), cts.Token);

      t.ContinueWith(x =>
        {
            Console.WriteLine("Canceled successfully !");
        }, TaskContinuationOptions.OnlyOnCanceled);

      cts.Cancel();
      t.Wait();
  }
  catch { }
}

static void MyCanceledMethod(CancellationToken ct)
{
  for (int i = 0; i < 5; i++)
  {
      Thread.Sleep(1000);
      Console.Write('*');
  }
}

---

No problem ! The task running MyCanceledMethod is perfectly canceled and I don't get to see the *****.

Now if I were to start the task in this way

Quote:

---

Task t = Task.Factory.StartNew(x => MyCanceledMethod(cts.Token), cts.Token);

---

That's with a lambda taking one not used parameter x instead of () , the task just doesn't get canceled :confused:

Can anyone explain to me the relation between task delegate signature and the TaskContinuationOptions.OnlyOnCanceled not being respected ?

That looks like what you have posted above. Mistake on your part?

Here's a link, btw. http://msdn.microsoft.com/en-us/libr...vs.110%29.aspx

No mistake ! Please note the x as a parameter to the delegate in the 2nd way of starting the task.

You have the same line in both places Task t= ...

No, it's different ! And meanwhile I found out what's causing the different behavior.

My first way of starting the task, note the '() =>'

Code:

---

Task t = Task.Factory.StartNew(() => MyCanceledMethod(cts.Token), cts.Token);

---

This is actually using following overload of StartNew method, allowing perfect cancelling of MyCanceledMethod

Code:

---

public Task StartNew(Action action, CancellationToken cancellationToken)

---

My second way of starting the task, please note the 'x =>'

Code:

---

Task t = Task.Factory.StartNew(x => MyCanceledMethod(cts.Token), cts.Token);

---

comes down to this overload of StartNew that simply casts the CancellationToken to object :eek:

Code:

---

public Task StartNew(Action<Object> action, Object state)

---

It's a subtle difference, but kind a hard to discover with such extensively overloaded methods !

This might help! http://msdn.microsoft.com/en-us/libr...vs.110%29.aspx