Thread.Sleep vs Task.Delay?

Question

I know that Thread.Sleep blocks a thread.

But does Task.Delay also block? Or is it just like Timer which uses one thread for all callbacks (when not overlapping)?

(this question doesn't cover the differences)

Answer 1

The documentation on MSDN is disappointing, but decompiling Task.Delay using Reflector gives more information:

public static Task Delay(int millisecondsDelay, CancellationToken cancellationToken) {     if (millisecondsDelay < -1)     {         throw new ArgumentOutOfRangeException("millisecondsDelay", Environment.GetResourceString("Task_Delay_InvalidMillisecondsDelay"));     }     if (cancellationToken.IsCancellationRequested)     {         return FromCancellation(cancellationToken);     }     if (millisecondsDelay == 0)     {         return CompletedTask;     }     DelayPromise state = new DelayPromise(cancellationToken);     if (cancellationToken.CanBeCanceled)     {         state.Registration = cancellationToken.InternalRegisterWithoutEC(delegate (object state) {             ((DelayPromise) state).Complete();         }, state);     }     if (millisecondsDelay != -1)     {         state.Timer = new Timer(delegate (object state) {             ((DelayPromise) state).Complete();         }, state, millisecondsDelay, -1);         state.Timer.KeepRootedWhileScheduled();     }     return state; } 

Basically, this method is just a timer wrapped inside of a task. So yes, you can say it's just like timer.