[monarch] use spawn as multiprocessing start method #564
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Always use spawn as a start method, fork is a giant footgun. We were observing hangs in megatron checkpointing, I suspect this is why. Ref: python/cpython#84559 Differential Revision: [D78465499](https://our.internmc.facebook.com/intern/diff/D78465499/) **NOTE FOR REVIEWERS**: This PR has internal Meta-specific changes or comments, please review them on [Phabricator](https://our.internmc.facebook.com/intern/diff/D78465499/)! [ghstack-poisoned]
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Always use spawn as a start method, fork is a giant footgun. We were observing hangs in megatron checkpointing, I suspect this is why. Ref: python/cpython#84559 Differential Revision: [D78465499](https://our.internmc.facebook.com/intern/diff/D78465499/) **NOTE FOR REVIEWERS**: This PR has internal Meta-specific changes or comments, please review them on [Phabricator](https://our.internmc.facebook.com/intern/diff/D78465499/)! ghstack-source-id: 296751605 Pull Request resolved: #564
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This pull request was exported from Phabricator. Differential Revision: D78465499 |
Always use spawn as a start method, fork is a giant footgun. We were observing hangs in megatron checkpointing, I suspect this is why. Ref: python/cpython#84559 Differential Revision: [D78465499](https://our.internmc.facebook.com/intern/diff/D78465499/) **NOTE FOR REVIEWERS**: This PR has internal Meta-specific changes or comments, please review them on [Phabricator](https://our.internmc.facebook.com/intern/diff/D78465499/)! [ghstack-poisoned]
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Pull Request resolved: #564 Always use spawn as a start method, fork is a giant footgun. We were observing hangs in megatron checkpointing, I suspect this is why. Ref: python/cpython#84559 Differential Revision: [D78465499](https://our.internmc.facebook.com/intern/diff/D78465499/) **NOTE FOR REVIEWERS**: This PR has internal Meta-specific changes or comments, please review them on [Phabricator](https://our.internmc.facebook.com/intern/diff/D78465499/)! ghstack-source-id: 296751863
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This pull request was exported from Phabricator. Differential Revision: D78465499 |
Always use spawn as a start method, fork is a giant footgun. We were observing hangs in megatron checkpointing, I suspect this is why. Ref: python/cpython#84559 Differential Revision: [D78465499](https://our.internmc.facebook.com/intern/diff/D78465499/) **NOTE FOR REVIEWERS**: This PR has internal Meta-specific changes or comments, please review them on [Phabricator](https://our.internmc.facebook.com/intern/diff/D78465499/)! [ghstack-poisoned]
This was referenced Jul 18, 2025
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This pull request was exported from Phabricator. Differential Revision: D78465499 |
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This pull request has been merged in cef93c7. |
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Stack from ghstack (oldest at bottom):
Always use spawn as a start method, fork is a giant footgun. We were observing hangs in megatron checkpointing, I suspect this is why.
Ref: python/cpython#84559
Differential Revision: D78465499
NOTE FOR REVIEWERS: This PR has internal Meta-specific changes or comments, please review them on Phabricator!