Merge branch 'fix-external-dataloader' into 'main'

Fix wrapping of external dataloaders

See merge request ADLR/megatron-lm!2453

megatron/core/rerun_state_machine.py

@@ -834,8 +834,8 @@ class MyDataIterator:
         replay_data_iterator = RerunDataIterator(data_iterator)
     """
 
-    def __init__(self, iterable: Any, make_iterable: bool = True) -> None:
-        self.iterable: Iterable[Any] = iter(iterable) if make_iterable else iterable
+    def __init__(self, iterable: Iterable[Any]) -> None:
+        self.iterable: Iterable[Any] = iterable
         self.saved_microbatches: list[Any] = []
         self.replaying: bool = False
         self.replay_pos: int = 0

megatron/training/training.py

@@ -1878,12 +1878,15 @@ def build_train_valid_test_data_iterators(
     def _get_iterator(dataloader_type, dataloader):
         """Return dataset iterator."""
         if dataloader_type == "single":
-            return RerunDataIterator(dataloader)
+            return RerunDataIterator(iter(dataloader))
         elif dataloader_type == "cyclic":
-            return RerunDataIterator(cyclic_iter(dataloader))
+            return RerunDataIterator(iter(cyclic_iter(dataloader)))
         elif dataloader_type == "external":
             # External dataloader is passed through. User is expected to define how to iterate.
-            return RerunDataIterator(dataloader, make_iterable=False)
+            if isinstance(dataloader, list):
+                return [RerunDataIterator(d) for d in dataloader]
+            else:
+                return RerunDataIterator(dataloader)
         else:
             raise RuntimeError("unexpected dataloader type")