Exam Ref 70–483: Programming in C#

The SynchronizationContext abstracts the way these different applications work and makes sure that you end up on the right thread when you need to update something on the UI or process a web request

public Task SleepAsyncA(int millisecondsTimeout)
{
return Task.Run(() => Thread.Sleep(millisecondsTimeout));
}
public Task SleepAsyncB(int millisecondsTimeout)
{
TaskCompletionSource<bool> tcs = null;
var t = new Timer(delegate { tcs.TrySetResult(true); }, null, -1, -1);
tcs = new TaskCompletionSource<bool>(t);
t.Change(millisecondsTimeout, -1);
return tcs.Task;
}

You should use the Parallel class only when your code doesn’t have to be executed sequentially