docs: def metric(self, name, count, elapsed):
          """A metric function that writes a single CSV file
  
          :arg str name: name of the metric
          :arg int count: number of items
          :arg float elapsed: time in seconds
          """
  
          if name is None:
              warnings.warn("Ignoring unnamed metric", stacklevel=3)
              return
  
          with self.lock:
              self.writer.writerow((name, count, "%f"%elapsed))