try: persistent_workers=True

tests/parity_fabric/models.py

@@ -76,6 +76,7 @@ def get_dataloader(self):
             dataset,
             batch_size=self.batch_size,
             num_workers=2,
+            persistent_workers=True,
         )
 
     def get_loss_function(self):

tests/parity_pytorch/models.py

@@ -59,4 +59,5 @@ def train_dataloader(self):
             CIFAR10(root=_PATH_DATASETS, train=True, download=True, transform=self.transform),
             batch_size=32,
             num_workers=1,
+            persistent_workers=True,
         )

tests/tests_fabric/utilities/test_data.py

@@ -638,9 +638,9 @@ def test_suggested_max_num_workers_not_triggering_torch_warning(local_world_size
 
     # The dataloader runs a check in `DataLoader.check_worker_number_rationality`
     with pytest.warns(UserWarning, match="This DataLoader will create"):
-        DataLoader(range(2), num_workers=(cpu_count + 1))
+        DataLoader(range(2), num_workers=(cpu_count + 1), persistent_workers=True)
     with no_warning_call():
-        DataLoader(range(2), num_workers=suggested_max_num_workers(local_world_size))
+        DataLoader(range(2), num_workers=suggested_max_num_workers(local_world_size), persistent_workers=True)
 
 
 def test_state():

tests/tests_pytorch/callbacks/test_prediction_writer.py

@@ -83,7 +83,7 @@ def test_prediction_writer_batch_indices(num_workers, tmp_path):
     DummyPredictionWriter.write_on_batch_end = Mock()
     DummyPredictionWriter.write_on_epoch_end = Mock()
 
-    dataloader = DataLoader(RandomDataset(32, 64), batch_size=4, num_workers=num_workers)
+    dataloader = DataLoader(RandomDataset(32, 64), batch_size=4, num_workers=num_workers, persistent_workers=True)
     model = BoringModel()
     writer = DummyPredictionWriter("batch_and_epoch")
     trainer = Trainer(default_root_dir=tmp_path, logger=False, limit_predict_batches=4, callbacks=writer)

tests/tests_pytorch/helpers/advanced_models.py

@@ -218,4 +218,4 @@ def configure_optimizers(self):
         return torch.optim.Adam(self.parameters(), lr=0.02)
 
     def train_dataloader(self):
-        return DataLoader(MNIST(root=_PATH_DATASETS, train=True, download=True), batch_size=128, num_workers=1)
+        return DataLoader(MNIST(root=_PATH_DATASETS, train=True, download=True), batch_size=128, num_workers=1, persistent_workers=True)

tests/tests_pytorch/trainer/connectors/test_data_connector.py

@@ -135,7 +135,7 @@ def test_dataloader_persistent_workers_performance_warning(num_workers, tmp_path
         barebones=True,
     )
     model = TestSpawnBoringModel(warning_expected=(num_workers > 0))
-    dataloader = DataLoader(RandomDataset(32, 64), num_workers=num_workers)
+    dataloader = DataLoader(RandomDataset(32, 64), num_workers=num_workers, persistent_workers=True)
     trainer.fit(model, dataloader)
 
 
@@ -252,7 +252,7 @@ def test_update_dataloader_with_multiprocessing_context():
     """This test verifies that `use_distributed_sampler` conserves multiprocessing context."""
     train = RandomDataset(32, 64)
     context = "spawn"
-    train = DataLoader(train, batch_size=32, num_workers=2, multiprocessing_context=context, shuffle=True)
+    train = DataLoader(train, batch_size=32, num_workers=2, multiprocessing_context=context, shuffle=True, persistent_workers=True)
     new_data_loader = _update_dataloader(train, SequentialSampler(train.dataset))
     assert new_data_loader.multiprocessing_context == train.multiprocessing_context
 

tests/tests_pytorch/trainer/test_dataloaders.py

@@ -661,7 +661,7 @@ def test_auto_add_worker_init_fn_distributed(tmp_path, monkeypatch):
     num_workers = 2
     batch_size = 2
 
-    dataloader = DataLoader(dataset, batch_size=batch_size, num_workers=num_workers)
+    dataloader = DataLoader(dataset, batch_size=batch_size, num_workers=num_workers, persistent_workers=True)
     seed_everything(0, workers=True)
     trainer = Trainer(default_root_dir=tmp_path, max_epochs=1, accelerator="gpu", devices=2, strategy="ddp_spawn")
     model = MultiProcessModel()