Correct way to delay the start of a Task

Question

I want to schedule a task to start in x ms and be able to cancel it before it starts (or just at the beginning of the task).

The first attempt would be something like

var _cancelationTokenSource = new CancellationTokenSource();  var token = _cancelationTokenSource.Token; Task.Factory.StartNew(() =>     {         token.ThrowIfCancellationRequested();         Thread.Sleep(100);         token.ThrowIfCancellationRequested();     }).ContinueWith(t =>     {         token.ThrowIfCancellationRequested();         DoWork();         token.ThrowIfCancellationRequested();     }, token); 

But I feel like there should be a better way, as this would use up a thread while in the sleep, during which it could be canceled.

What are my other options?

Answer 1

Like Damien_The_Unbeliever mentioned, the Async CTP includes Task.Delay. Fortunately, we have Reflector:

public static class TaskEx {     static readonly Task _sPreCompletedTask = GetCompletedTask();     static readonly Task _sPreCanceledTask = GetPreCanceledTask();      public static Task Delay(int dueTimeMs, CancellationToken cancellationToken)     {         if (dueTimeMs < -1)             throw new ArgumentOutOfRangeException("dueTimeMs", "Invalid due time");         if (cancellationToken.IsCancellationRequested)             return _sPreCanceledTask;         if (dueTimeMs == 0)             return _sPreCompletedTask;          var tcs = new TaskCompletionSource<object>();         var ctr = new CancellationTokenRegistration();         var timer = new Timer(delegate(object self)         {             ctr.Dispose();             ((Timer)self).Dispose();             tcs.TrySetResult(null);         });         if (cancellationToken.CanBeCanceled)             ctr = cancellationToken.Register(delegate                                                  {                                                      timer.Dispose();                                                      tcs.TrySetCanceled();                                                  });          timer.Change(dueTimeMs, -1);         return tcs.Task;     }      private static Task GetPreCanceledTask()     {         var source = new TaskCompletionSource<object>();         source.TrySetCanceled();         return source.Task;     }      private static Task GetCompletedTask()     {         var source = new TaskCompletionSource<object>();         source.TrySetResult(null);         return source.Task;     } } 

Answer 2

Since .NET 4.5 has now been released, there's a very simple built-in way to delay a task: just use Task.Delay(). behind the scenes, it uses the implementation that ohadsc decompiled.