Fix TensorBoardLogger creating redundant experiment when finalizing (#14762)

Co-authored-by: Kushashwa Ravi Shrimali <kushashwaravishrimali@gmail.com>

src/pytorch_lightning/CHANGELOG.md

@@ -12,6 +12,7 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/).
 - Fixed the availability check for the neptune-client package ([#14714](https://github.com/Lightning-AI/lightning/pull/14714))
 - Break HPU Graphs into two parts (forward + backward as one and optimizer as another) for better performance ([#14656](https://github.com/Lightning-AI/lightning/pull/14656))
 - Fixed torchscript error with ensembles of LightningModules ([#14657](https://github.com/Lightning-AI/lightning/pull/14657), [#14724](https://github.com/Lightning-AI/lightning/pull/14724))
+- Fixed an issue with `TensorBoardLogger.finalize` creating a new experiment when none was created during the Trainer's execution ([#14762](https://github.com/Lightning-AI/lightning/pull/14762))
 
 
 ## [1.7.6] - 2022-09-13

src/pytorch_lightning/loggers/tensorboard.py

@@ -267,8 +267,9 @@ class TensorBoardLogger(Logger):
 
     @rank_zero_only
     def finalize(self, status: str) -> None:
-        self.experiment.flush()
-        self.experiment.close()
+        if self._experiment is not None:
+            self.experiment.flush()
+            self.experiment.close()
         self.save()
 
     @property

tests/tests_pytorch/checkpointing/test_model_checkpoint.py

@@ -869,18 +869,23 @@ def test_checkpoint_repeated_strategy(tmpdir):
         "limit_test_batches": 2,
         "enable_progress_bar": False,
         "enable_model_summary": False,
+        "log_every_n_steps": 1,
+        "default_root_dir": tmpdir,
     }
     trainer = Trainer(**trainer_kwargs, callbacks=[checkpoint_callback])
     trainer.fit(model)
-    assert os.listdir(tmpdir) == ["epoch=00.ckpt"]
+    assert set(os.listdir(tmpdir)) == {"epoch=00.ckpt", "lightning_logs"}
 
     for idx in range(4):
         # load from checkpoint
-        trainer = pl.Trainer(**trainer_kwargs, default_root_dir=tmpdir)
+        trainer = Trainer(**trainer_kwargs)
         trainer.fit(model, ckpt_path=checkpoint_callback.best_model_path)
         trainer.test(ckpt_path=checkpoint_callback.best_model_path, verbose=False)
+
         assert set(os.listdir(tmpdir)) == {"epoch=00.ckpt", "lightning_logs"}
-    assert set(os.listdir(tmpdir / "lightning_logs")) == {f"version_{i}" for i in range(4)}
+
+    # no new versions created after the initial fit, because the ones that resume from ckpt do not log anything
+    assert set(os.listdir(tmpdir / "lightning_logs")) == {"version_0"}
 
 
 def test_checkpoint_repeated_strategy_extended(tmpdir):
@@ -891,6 +896,7 @@ def test_checkpoint_repeated_strategy_extended(tmpdir):
         def validation_step(self, batch, batch_idx):
             output = self.layer(batch)
             loss = self.loss(batch, output)
+            self.log("val_loss", loss)
             return {"val_loss": loss}
 
         def validation_epoch_end(self, *_):
@@ -930,7 +936,7 @@ def test_checkpoint_repeated_strategy_extended(tmpdir):
         limit_test_batches=4,
         callbacks=[checkpoint_cb],
     )
-    trainer = pl.Trainer(**trainer_config)
+    trainer = Trainer(**trainer_config)
     assert_trainer_init(trainer)
 
     model = ExtendedBoringModel()

tests/tests_pytorch/loggers/test_tensorboard.py

@@ -290,7 +290,17 @@ def test_tensorboard_with_accummulated_gradients(mock_log_metrics, tmpdir):
 def test_tensorboard_finalize(summary_writer, tmpdir):
     """Test that the SummaryWriter closes in finalize."""
     logger = TensorBoardLogger(save_dir=tmpdir)
+    assert logger._experiment is None
     logger.finalize("any")
+
+    # no log calls, no experiment created -> nothing to flush
+    summary_writer.assert_not_called()
+
+    logger = TensorBoardLogger(save_dir=tmpdir)
+    logger.log_metrics({"flush_me": 11.1})  # trigger creation of an experiment
+    logger.finalize("any")
+
+    # finalize flushes to experiment directory
     summary_writer().flush.assert_called()
     summary_writer().close.assert_called()