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Reset random sampler counters when restoring checkpoints into a used iterator - #1566
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When `_StatefulRandomSamplerIterator.load_state_dict` replays a checkpoint onto an already-used iterator, `self.yielded` and `self.perm_index` retained their previous values before replaying `self.next_yielded` steps. A partially consumed iterator returned the wrong sequence, and an exhausted iterator raised `StopIteration` during replay. Reset `self.yielded` and `self.perm_index` to `0` before regenerating `self.perm` and advancing through `self.next_yielded`, and add a regression test covering both replacement modes, partially consumed and exhausted targets, and repeated restores. Co-Authored-By: Claude Code <noreply@anthropic.com>
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Hi @psaikaushik @divyanshk — following up on #1562, this PR fixes a race in |
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Summary
Follow-up from the discussion on #1562.
When
_StatefulRandomSamplerIterator.load_state_dictreplays a checkpoint onto an iterator that has already yielded samples,self.yieldedandself.perm_indexretained their previous values before replayingself.next_yieldedsteps:StopIterationduring replay.Changes
torchdata/stateful_dataloader/sampler.py: Resetself.yielded = 0andself.perm_index = 0before rebuildingself.permand replayingself.next_yieldedsteps in_StatefulRandomSamplerIterator.load_state_dict.test/stateful_dataloader/test_sampler.py: Addtest_random_sampler_checkpoint_restores_used_iteratorcovering both replacement modes (replacement=Falseandreplacement=True), partially consumed (5) and exhausted (70) target iterators, and restoring the same snapshot twice.Validation
replacement×consumed) before the two resets and passes afterward.test/stateful_dataloader/test_sampler.pysuite and applicable pre-commit hooks pass.🤖 Generated with Claude Code