Why isn't a Task awaited before it get's cancelled?

Question

I need to write a service with some complex behaviour like simultanious tasks and I'm facing an issue with.

I've written a sample in xUnit to show you the problem.

1 want to execute a task on a background, eventually start some child tasks. At a moment in time the task needs to be cancelled.

Therefore, I have the following in place:

[Fact]
public void ShouldWaitUnitTaskCompleted()
{
    Task.Factory.StartNew(() =>
    {
        while (!cancellationTokenSource.IsCancellationRequested)
        {
            Task.Delay(10000).Wait();
            TaskIsCompleted = true;
        }
    }, cancellationTokenSource.Token);

    Thread.Sleep(3000);

    cancellationTokenSource.Cancel();

    Assert.True(TaskIsCompleted);
}

}

However, the xUnit completes after 3 seconds (my thread sleep). In my task, I'm having a loop that say, as long as it's not a cancellation request delay if for 10 second.

So the behaviour I expect would be:

Start the application.
Start the task (since it's no cancellation request, a delay of 10 seconds will start).
Wait for 3 seconds and then cancel the token.
Wait for the task with the 10 second delay to complete and then exit.

Why doesn't my code wait for the 10 seconds frame to pass?

No background threads could exist when the main (foreground) thread had already exit after 3 seconds. Your app died already. You would have to Thread.Sleep the main thread for another 7+ seconds to resume other work. — Biscuits

Cheesebaron Cheesebaron · Accepted Answer · 2015-09-15T13:42:31

You don't await your Task which you create. Hence the execution of the code just continues on to the Thread.Sleep(3000).

Why isn't a Task awaited before it get's cancelled?

2 Answers