Get Task CancellationToken

Question

Can I get CancellationToken which was passed to Task constructor during task action executing. Most of samples look like this:

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

Task myTask = Task.Factory.StartNew(() =>
{
    for (...)
    {
        token.ThrowIfCancellationRequested();

        // Body of for loop.
    }
}, token);

But what if my action is not lambda but a method placed in other class and I don't have direct access to token? Is the only way is to pass token as state?

Answer 1

There is a very simple solution:

    class CancelingTasks
{
    private static void Foo(CancellationToken token)
    {
        while (true)
        {
            token.ThrowIfCancellationRequested();

            Thread.Sleep(100);
            Console.Write(".");                
        }
    }

    static void Main(string[] args)
    {
        CancellationTokenSource source = new CancellationTokenSource();
        CancellationToken tok = source.Token;

        tok.Register(() =>
        {
            Console.WriteLine("Cancelled.");
        });

        Task t = new Task(() =>
        {
            Foo(tok);
        }, tok);

        t.Start();

        Console.ReadKey();
        source.Cancel();
        source.Dispose();

        Console.WriteLine("Main program done, press any key.");
        Console.ReadKey();
    }
}