code: def _vispy_start(self, interval):
      if self._task is not None:
          self._task.cancel()
      self._task = asyncio.create_task(self._timer_coro(interval))
  
imports: import asyncio
  from ..base import BaseApplicationBackend, BaseCanvasBackend, BaseTimerBackend
  from ...app import Timer
  from ...util import keys
  from ._offscreen_util import OffscreenContext, FrameBufferHelper
label_desc: Use image node_id 2 for calling the TimerBackend obj's underlying member method code with example usage: obj._vispy_start(interval) without return types