expand eval loop out (#3165)

pytorch_lightning/trainer/evaluation_loop.py

@@ -325,8 +325,70 @@ class TrainerEvaluationLoopMixin(ABC):
         # TODO: deprecate
         self.evaluation_loop.on_evaluation_start()
 
-        # run evaluation (val_step + val_step_end + val_epoch_end)
-        eval_results = self._evaluate(self.model, dataloaders, max_batches, test_mode)
+        # ------------------------------
+        # ------------------------------
+        # ------------------------------
+        # enable eval mode + no grads
+        model.zero_grad()
+        model.eval()
+        torch.set_grad_enabled(False)
+
+        # set up the eval loop
+        self.evaluation_loop.setup(model, max_batches, dataloaders)
+
+        # hook
+        self.evaluation_loop.on_evaluation_epoch_start()
+
+        # run validation/testing
+        for dataloader_idx, dataloader in enumerate(dataloaders):
+            dl_outputs = []
+
+            # certain accelerators need to process the dataloader
+            dataloader = self.accelerator_backend.process_dataloader(dataloader)
+
+            # each dataloader has a max num batches
+            dl_max_batches = self.evaluation_loop.max_batches[dataloader_idx]
+
+            for batch_idx, batch in enumerate(dataloader):
+                if batch is None:
+                    continue
+
+                # stop short when running on limited batches
+                if batch_idx >= dl_max_batches:
+                    break
+
+                # hook
+                self.evaluation_loop.on_evaluation_batch_start(batch, batch_idx, dataloader_idx)
+
+                # lightning module methods
+                output = self.evaluation_loop.evaluation_step(test_mode, batch, batch_idx, dataloader_idx)
+                output = self.evaluation_loop.evaluation_step_end(output)
+
+                # hook
+                self.evaluation_loop.on_evaluation_batch_end(batch, batch_idx, dataloader_idx)
+
+                # clean up
+                self.evaluation_loop.evaluation_batch_end_cleanup(output, batch_idx, dataloader_idx)
+                self.evaluation_loop.log_step_metrics(output, batch_idx)
+
+                # track epoch level metrics
+                if output is not None:
+                    dl_outputs.append(output)
+
+            self.evaluation_loop.outputs.append(dl_outputs)
+
+        # lightning module method
+        eval_results = self.evaluation_loop.evaluation_epoch_end(num_dataloaders=len(dataloaders))
+
+        # hook
+        self.evaluation_loop.on_evaluation_epoch_end(eval_results)
+
+        # enable train mode again
+        model.train()
+        torch.set_grad_enabled(True)
+        # ------------------------------
+        # ------------------------------
+        # ------------------------------
 
         # log the final eval loop metrics
         eval_loop_results = self.__log_evaluation_epoch_metrics(eval_results, test_mode)