Task does not complete if another task with in it gets cancelled

July 16, 2022

In this code, the task t will never complete (never outputs to the console) if I cancel the token, even though the token is not used for t and only used for a task inside t

CancellationTokenSource source = new CancellationTokenSource();
CancellationToken token = source.Token;

Task t = Task.Factory.StartNew(async () =>
{
    await Task.Delay(1000, token);
    Console.WriteLine("Task Completed");
});

source.Cancel();

How can I cancel the token but also let the task complete

Notes:
I tried using Task.Run instead, and got the same output
t.IsCompleted will stay false indefinitely (task will never complete)
The delay task does complete

>Solution :

You can make the t to survive the cancellation, by handling and suppressing the OperationCanceledException that is thrown by the Task.Delay:

Task t = Task.Run(async () =>
{
    try { await Task.Delay(1000, token); } catch (OperationCanceledException) { }
    Console.WriteLine("Task Completed");
});