code: def add_pending_greenlet(self, greenlet: Greenlet):
          
  
          def remove(_):
              self.greenlets.remove(greenlet)
  
          self.greenlets.append(greenlet)
          greenlet.link_exception(self.on_error)
          greenlet.link_value(remove)
docs: Ensures an error on the passed greenlet crashes self/main greenlet.