Repeating Tasks

Question

Hi!

Is there any common approach for periodical tasks execution? I need to
perform task periodically (modelling hardware, some kind of
state-machine). Here is one soultion:
http://stackoverflow.com/questions/4890915/is-there-a-task-based-replacement-for-system-threading-timer

But maybe there exists another more fine-grained solution? Custom
TaskScheduler? Is there any possibility to continue task with itself?

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God bless you!

Answer 1

We are introducing Task.Delay() in .NET 4.5 - http://msdn.microsoft.com/en-us/library/hh194865(v=VS.110).aspx. You continue from the result of Task.Delay() with the actual task that you want to execute, or you can do "await Task.Delay(...); <continuation code>...".

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Answer 2

Thanks for rapid response. Can you please provide us with some code sample of how can I use this in my scenario?

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God bless you!

Answer 3

Try this:

 

            var cts = new CancellationTokenSource(5000); // Auto-cancel after 5 sec

 

            Action<Task> repeatAction = null;

            repeatAction = _ignored1 =>

                {

                    Console.WriteLine("{0}: Repeating every 1 sec", DateTime.Now);

                    Task.Delay(1000, cts.Token).ContinueWith(_ignored2 => repeatAction(_ignored2), cts.Token); // Repeat every 1 sec

                };

 

            Console.WriteLine("{0}: Launching with 2 sec delay", DateTime.Now);

            Task.Delay(2000, cts.Token).ContinueWith(repeatAction, cts.Token); // Launch with 2 sec delay

 

            cts.Token.WaitHandle.WaitOne(); // Wait for the CTS to get canceled. Must be after 5 sec.

            Console.WriteLine("{0}: Done after 5 sec of recurring", DateTime.Now);

 

On my machine it produces the expected output:

2011-10-12 14:52:06: Launching with 2 sec delay

2011-10-12 14:52:08: Repeating every 1 sec

2011-10-12 14:52:09: Repeating every 1 sec

2011-10-12 14:52:10: Repeating every 1 sec

2011-10-12 14:52:11: Repeating every 1 sec

2011-10-12 14:52:11: Done after 5 sec of recurring

 

 

Zlatko Michailov

Software Development Engineer, Parallel Computing Platform

Microsoft Corp.

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This posting is provided "AS IS" with no warranties, and confers no rights.

Answer 4

Here is a nicer version that uses await:

 

        static void Example2()

        {

            var cts = new CancellationTokenSource(5000); // Work for 5 sec

 

            try

            {

                DelayAsync(2000, 1000, cts.Token).Wait();

            }

            catch (AggregateException ae)

            {

                ae.Handle(e => e is TaskCanceledException);

            }

 

            Console.WriteLine("{0}: Done after 5 sec of recurring", DateTime.Now);

        }

 

        static async Task DelayAsync(int delayMillis, int repeatMillis, CancellationToken ct)

        {

            Console.WriteLine("{0}: Launching with 2 sec delay", DateTime.Now);

            await Task.Delay(delayMillis, ct);

 

            while (true)

            {

                Console.WriteLine("{0}: Repeating every 1 sec", DateTime.Now);

                await Task.Delay(repeatMillis, ct);

            }

        }

 

 

Zlatko Michailov

Software Development Engineer, Parallel Computing Platform

Microsoft Corp.

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This posting is provided "AS IS" with no warranties, and confers no rights.