parameters: (self, event)
docstring: Check and discard expired events using SessionLog.START.
  
      Check for a SessionLog.START event and purge all previously seen events
      with larger steps, because they are out of date. Because of supervisor
      threading, it is possible that this logic will cause the first few event
      messages to be discarded since supervisor threading does not guarantee
      that the START message is deterministically written first.
  
      This method is preferred over _CheckForOutOfOrderStepAndMaybePurge which
      can inadvertently discard events due to supervisor threading.
  
      Args:
        event: The event to use as reference. If the event is a START event, all
          previously seen events with a greater event.step will be purged.
docstring_summary: Check and discard expired events using SessionLog.START.
docstring_tokens: Check and discard expired events using SessionLog . START .
function: def _CheckForRestartAndMaybePurge(self, event):
      """Check and discard expired events using SessionLog.START.
  
      Check for a SessionLog.START event and purge all previously seen events
      with larger steps, because they are out of date. Because of supervisor
      threading, it is possible that this logic will cause the first few event
      messages to be discarded since supervisor threading does not guarantee
      that the START message is deterministically written first.
  
      This method is preferred over _CheckForOutOfOrderStepAndMaybePurge which
      can inadvertently discard events due to supervisor threading.
  
      Args:
        event: The event to use as reference. If the event is a START event, all
          previously seen events with a greater event.step will be purged.
      """
      if event.HasField(
          'session_log') and event.session_log.status == SessionLog.START:
        self._Purge(event, by_tags=False)
function_tokens: def _CheckForRestartAndMaybePurge ( self , event ) : if event . HasField ( 'session_log' ) and event . session_log . status == SessionLog . START : self . _Purge ( event , by_tags = False )