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[SDL] StatefulDistributedSampler add epoch to state_dict #1515

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[SDL] StatefulDistributedSampler add epoch to state_dict #1515

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8cd24d5
StatefulDistributedSampler add epoch to state_dict
aelavender Nov 18, 2025
23e0ddd
update tests with new state dict format
aelavender Nov 19, 2025
9981716
remove testing print
aelavender Dec 2, 2025
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11 changes: 8 additions & 3 deletions test/stateful_dataloader/test_sampler.py
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Original file line number Diff line number Diff line change
Expand Up @@ -96,10 +96,10 @@ def test_sampler_state_dict(self):
def test_sampler_load_state_dict(self):

sampler = StatefulDistributedSampler(self.dataset, num_replicas=10, rank=0)
sampler.load_state_dict({"yielded": 3})
sampler.load_state_dict({"epoch": 0, "yielded": 3})
self.assertEqual(sampler.next_yielded, 3)
with self.assertRaises(ValueError):
sampler.load_state_dict({"yielded": -1})
sampler.load_state_dict({"epoch": 0, "yielded": -1})

def test_sampler_next_yielded(self):

Expand All @@ -108,7 +108,12 @@ def test_sampler_next_yielded(self):
next(iterator) # advance the iterator
self.assertEqual(sampler.yielded, 1)
self.assertIsNone(sampler.next_yielded)
sampler.load_state_dict({StatefulDistributedSampler._YIELDED: 5})
sampler.load_state_dict(
{
StatefulDistributedSampler._EPOCH: 0,
StatefulDistributedSampler._YIELDED: 5,
}
)
self.assertEqual(sampler.next_yielded, 5)
iterator = iter(sampler)
next(iterator) # advance the iterator again
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6 changes: 5 additions & 1 deletion torchdata/stateful_dataloader/sampler.py
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Expand Up @@ -181,6 +181,7 @@ def __iter__(self):

class StatefulDistributedSampler(torch.utils.data.distributed.DistributedSampler):
_YIELDED = "yielded"
_EPOCH = "epoch"

def __init__(
self,
Expand All @@ -206,9 +207,12 @@ def __iter__(self):
yield idx

def state_dict(self) -> Dict[str, Any]:
return {self._YIELDED: self.yielded}
return {self._YIELDED: self.yielded, self._EPOCH: self.epoch, "NEXT_YIELDED": self.next_yielded}

def load_state_dict(self, state_dict: Dict[str, Any]) -> None:
if self._EPOCH not in state_dict:
raise ValueError("Invalid state_dict")
self.set_epoch(state_dict[self._EPOCH])
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@divyanshk divyanshk Nov 19, 2025

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If users are used to calling set_epoch in a certain in the main loop, then doing self.set_epoch(..) on load_state_dict might interfere with that ?

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@aelavender aelavender Dec 2, 2025

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If the user is trying to set_epoch to something other than what was previously saved, then they are likely going to get repeated indices in the current epoch, which seems like broken behaviour. Perhaps we should warn in that case.

if self._YIELDED not in state_dict:
raise ValueError("Invalid state_dict")
if state_dict[self._YIELDED] < 0:
Expand Down