def on_loader_end(self, runner: "IRunner") -> None:
        """On loader end action: compute metric values
        and update runner's loader metrics with it

        Args:
            runner: current runner
        """
        metrics = self.metric.compute_key_value()
        metrics = runner.engine.mean_reduce_ddp_metrics(metrics)
        runner.loader_metrics.update(metrics)
On loader end action: compute metric values
        and update runner's loader metrics with it

        Args:
            runner: current runner
        
catalyst/callbacks/metric.py