{"slug":"principle-separate-before-serializing-shared-state","title":"principle-separate-before-serializing-shared-state","summary":"Apply when concurrent actors might write to the same file, branch, key, or state object. Eliminate the sharing first; serialize structurally only when one shared writer is a real invariant.","platform":"Claude","tags":[],"authorName":"LLM Mart","authorSlug":"llm-mart","score":0,"source":"github","price":null,"verified":false,"createdAt":"2026-09-29T15:22:24.510203Z","repo":{"url":"https://github.com/michael-denyer/pstack-claude","stars":677,"forks":83,"license":"MIT","updatedAt":"2026-09-29T12:06:50Z"},"bodyHtml":"
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name: principle-separate-before-serializing-shared-state\ndescription: \"Apply when concurrent actors might write to the same file, branch, key, or state object. Eliminate the sharing first; serialize structurally only when one shared writer is a real invariant.\"\nuser-invocable: false

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Separate Before Serializing Shared State

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When concurrent actors might share mutable state, first ask whether they need the same mutable object. If not, eliminate the sharing. When sharing is real, enforce serialization structurally: lockfiles, sequential phases, exclusive ownership. Instructions and conventions are not concurrency control.

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Why: Concurrent writes to shared state create race conditions that are intermittent, hard to reproduce, and expensive to debug.

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Pattern:

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  1. Identify shared mutable state (files both read and write, branches both push to, APIs both define and consume).
    2. \n
  2. Default: eliminate the shared write target. Ask: do these actors need one canonical object, or are they publishing independent facts? Give each actor its own owned file, key, branch, or state directory, and merge only at the read/reporting boundary. Two workers writing their own lastX field into one state.json is still shared mutation. indexer-state.json + metrics-state.json is not.
    3. \n
  3. Only when one shared write target is a real invariant, serialize access structurally (lockfiles, sequential phases, single-writer actor, or atomic compare-and-swap). Treat \"we need a lock\" as a design smell to check, not as the default answer.
    4. \n
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