Override num_workers from 0 to 1 in get_pytorch_dataloader (#330)

Summary:

To support a similar interface to the pytorch dataloader, we set `num_workers` to 1 if the input `num_workers` is 0 in `get_pytorch_dataloader`

Differential Revision: D68357865

src/spdl/dataloader/_pytorch_dataloader.py

@@ -13,6 +13,7 @@
 import os
 import pickle
 import time
+import warnings
 from collections.abc import Callable, Iterable, Iterator
 from concurrent.futures import ProcessPoolExecutor
 from multiprocessing.shared_memory import SharedMemory
@@ -298,8 +299,14 @@ def get_pytorch_dataloader(
     if timeout is not None and timeout < 0:
         raise ValueError(f"`timeout` must be positive. Found: {timeout}.")
 
-    if num_workers < 1:
+    if num_workers < 0:
         raise ValueError(f"`num_workers` must be greater than 0. Found: {num_workers}")
+    elif num_workers == 0:
+        warnings.warn(
+            "`num_workers` is 0. Setting `num_workers` to 1 for single process dataloading.",
+            stacklevel=2,
+        )
+        num_workers = 1
 
     buffer_size = prefetch_factor * num_workers