cancel method

Implementation

@override
Future<void> cancel(String? id) async {
  if (id != null && (_activeId == null || _activeId != id)) {
    _preCancelledId = id;
  }
  final proc = _activeProcess;
  if (proc != null && (id == null || id == _activeId)) {
    proc.kill(ProcessSignal.sigkill);
  }
}