Task is waiting for execution or unknown.
Task has been started.
Task has been successfully executed.
Task execution resulted in failure.
Task is being retried.
Task has been revoked.
Set of states meaning the task result is ready (has been executed).
Set of states meaning the task result is not ready (has not been executed).
Set of states meaning the task returned an exception.
Set of exception states that should propagate exceptions to the user.
Set of all possible states.