onCancel method
Called when the attached token is cancelled.
It's not necessary to detach from the token in this method, as cancellation tokens detach from all cancellables automatically when cancelled.
Implementation
@override
void onCancel(Exception cancelException) {
hasBeenCancelled = true;
_process?.kill(ProcessSignal.sigkill);
progress.cancel();
super.onCancel(cancelException);
}