Task cancellation from inside the task body

Question

I read about the Cancellation methods but based on my understanding they all provide control over tasks from outside the task, but if i want to cancel a task from the inside.

For example in this pseudo code:

Task tasks = new Task(() =>
{ 
     bool exists = CheckFromDB();
      if (!exists)
         break;
}

Can i cancel a task from the inside? The only idea i got is to trigger an exception inside the task and handle it from outside but surly that is not the way to do.

Answer 1

If you want to truly Cancel the task (e.g. after it's completed the Status property would be set to Canceled), you can do it this way:

var cts = new CancellationTokenSource();
var token = cts.Token;

Task innerCancel = new Task(
    () =>
    {
        if (!CheckFromDB())
        {
            cts.Cancel();
        }
        token.ThrowIfCancellationRequested();
    },
    token);

When you use return task won't be actually canceled, but rather code after the return statement won't be executed, and the task itself will have its state as RanToCompletion.

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On a side note it's advised to use Task.Factory.StartNew for .NET 4 and Task.Run for .NET 4.5 instead of constructor to create tasks.