Remove on epoch guard from the should stop validation check (#7701)

* Remove on epoch guard from the should stop validation check

* Formatting

pytorch_lightning/callbacks/gpu_stats_monitor.py

@@ -211,6 +211,4 @@ class GPUStatsMonitor(Callback):
 
     @staticmethod
     def _should_log(trainer) -> bool:
-        should_log = ((trainer.global_step + 1) % trainer.log_every_n_steps == 0 or trainer.should_stop)
-
-        return should_log
+        return (trainer.global_step + 1) % trainer.log_every_n_steps == 0 or trainer.should_stop

pytorch_lightning/callbacks/lr_monitor.py

@@ -202,6 +202,4 @@ class LearningRateMonitor(Callback):
 
     @staticmethod
     def _should_log(trainer) -> bool:
-        should_log = ((trainer.global_step + 1) % trainer.log_every_n_steps == 0 or trainer.should_stop)
-
-        return should_log
+        return (trainer.global_step + 1) % trainer.log_every_n_steps == 0 or trainer.should_stop

pytorch_lightning/trainer/training_loop.py

@@ -529,21 +529,11 @@ class TrainLoop:
 
             self.total_batch_idx += 1
 
-            # max steps reached, end training
-            if (
+            max_steps_reached = (
                 self.max_steps is not None and self.max_steps <= self.global_step + 1
                 and self._accumulated_batches_reached()
-            ):
-                break
-
-            # end epoch early
-            # stop when the flag is changed or we've gone past the amount
-            # requested in the batches
-            if self.trainer.should_stop:
-                break
-
-            # stop epoch if we limited the number of training batches
-            if self._num_training_batches_reached(is_last_batch):
+            )
+            if max_steps_reached or self.trainer.should_stop or self._num_training_batches_reached(is_last_batch):
                 break
 
             # progress global step according to grads progress
@@ -906,7 +896,7 @@ class TrainLoop:
         if on_epoch and is_last_batch and is_infinite_dataset:
             return True
 
-        if on_epoch and self.trainer.should_stop:
+        if self.trainer.should_stop:
             return True
 
         # TODO: let training/eval loop handle logic around limit_*_batches and val_check_batch

tests/trainer/loops/test_training_loop.py

@@ -110,3 +110,35 @@ def test_on_train_batch_start_return_minus_one(max_epochs, batch_idx_):
     else:
         assert trainer.train_loop.batch_idx == batch_idx_
         assert trainer.global_step == batch_idx_ * max_epochs
+
+
+def test_should_stop_mid_epoch(tmpdir):
+    """Test that training correctly stops mid epoch and that validation is still called at the right time"""
+
+    class TestModel(BoringModel):
+
+        def __init__(self):
+            super().__init__()
+            self.validation_called_at = None
+
+        def training_step(self, batch, batch_idx):
+            if batch_idx == 4:
+                self.trainer.should_stop = True
+            return super().training_step(batch, batch_idx)
+
+        def validation_step(self, *args):
+            self.validation_called_at = (self.trainer.current_epoch, self.trainer.global_step)
+            return super().validation_step(*args)
+
+    model = TestModel()
+    trainer = Trainer(
+        default_root_dir=tmpdir,
+        max_epochs=1,
+        limit_train_batches=10,
+        limit_val_batches=1,
+    )
+    trainer.fit(model)
+
+    assert trainer.current_epoch == 0
+    assert trainer.global_step == 5
+    assert model.validation_called_at == (0, 4)  # TODO(@carmocca): should be 5 - will be fixed in next PR