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

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))