.Continue starts before task is completed

Question

I have the following code in C#, VS2012, WPF 4.5. My expectation would be that, .ContinueWith will be executed after the task has finished completely (that's a continuation's whole purpose, isn't it?).

This should result in a value of 2 in finalResult.

int myTestInt = 0;

Task task = Task.Factory.StartNew(async () =>
{
   myTestInt = 1;
   await Task.Delay(TimeSpan.FromSeconds(6));
   myTestInt = 2;

}).ContinueWith(_ =>
   {
      int finalResult = myTestInt;
   });

In fact, finalResult is assigned a value of 1 instead. So it seems like the continuation is started on the await statement already.

Is this the intended behaviour? Am I missing something here? Can't I rely on ContinueWithto start after a task has completely finished?

Update:

Justin's answer just inspired me to check the following:

int myTestInt = 0;
Task task=Task.Factory.StartNew(async () =>
{
   myTestInt = 1;
   await Task.Delay(TimeSpan.FromSeconds(6));
   myTestInt = 2;
});

task.Wait();
int result2 = myTestInt;

finalResult is still set to 1. Is there no way to reliably wait for a task that contains awaits to complete?

Answer 1

When you pass an async delegate to Task.Factory.StartNew, the returned Task only represents the first portion of that delegate (up until the time it awaits something that is not already completed).

However, if you pass an async delegate to the new Task.Run method (which was included for this reason), the returned Task represents the entire delegate. So you can use ContinueWith as you expect. (Although await is usually a better option than ContinueWith).

For more information on StartNew vs Run, see Stephen Toub's post on the topic.