Returns whether the task that is currently executing has received a request to cancel its execution. Cancellation is requested on a task if it was created with a cancellation token, and the source that's associated with that token is canceled.
If you call this method in the body of a task and it returns true, you must respond with a call to cancel_current_task to acknowledge the cancellation request, after you perform any cleanup that's required. This aborts the execution of the task and causes it to enter into the canceled state. If you don't respond and continue execution, or return instead of calling cancel_current_task, the task enters the completed state when it is done.
A task is not cancellable if it was created without a cancellation token.