Attempting to prevent interrupting threads after future has completed.
We added a 4th state, so we have "Canceling and Canceled".  We are in canceling state if we previously were running, and will not transition to canceled till after the interrupt has been sent.  So at the end if we are not running, or already canceled, we will sleep, waiting for the interrupt to occur so we can be sure we handle it before we let the thread complete.
This also fixes a condition where we returned true on a cancel after a task has already been canceled