set default workers=0 for Windows

comet/models/base.py

@@ -21,6 +21,7 @@
 import abc
 import logging
 import os
+import sys
 import warnings
 from typing import Dict, List, Optional, Tuple, Union
 
@@ -592,9 +593,16 @@ def predict(
                 sort_ids = np.argsort([len(sample["ref"]) for sample in samples])
             sampler = OrderedSampler(sort_ids)
 
+        # On Windows, only num_workers=0 is supported.
+        is_windows = os.name == "nt"
         if num_workers is None:
             # Guideline for workers that typically works well.
-            num_workers = 2 * gpus
+            num_workers = 0 if is_windows else 2 * gpus
+        elif is_windows and num_workers != 0:
+            logger.warning(
+                "Due to limits of multiprocessing on Windows, it is likely that setting num_workers > 0 will result"
+                " in scores of 0. It is therefore recommended to set num_workers=0 or leave it to None (default)."
+            )
 
         self.eval()
         dataloader = DataLoader(