code: def tryPrepare(self, pp: PrePrepare):
          
          rv, msg = self.canPrepare(pp)
          if rv:
              self.doPrepare(pp)
          else:
              self.logger.debug("{} cannot send PREPARE since {}".format(self, msg))
docs: Try to send the Prepare message if the PrePrepare message is ready to
          be passed into the Prepare phase.