code: def on_error(self, subtask: Greenlet):
          
          log.error(
              'Runnable subtask died!',
              this=self,
              running=bool(self),
              subtask=subtask,
              exc=subtask.exception,
          )
          if not self.greenlet:
              return
          self.greenlet.kill(subtask.exception)
docs: Default callback for substasks link_exception
  
          Default callback re-raises the exception inside _run()