Agent skill · software engineering · cursor
principle-separate-before-serializing-shared-state
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.
Why this skill is useful
Provides a structured approach to managing shared state in concurrent systems, which the AI may not generate reliably on its own.
What it needs
About 1k tokens when loaded. Last updated 2026-08-06. 2,555 stars on the source repository.
What this skill does
Separate Before Serializing Shared State 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. Why: Concurrent writes to shared state create race conditions that are intermittent, hard to reproduce, and expensive to debug. Pattern: 1. Identify shared mutable state (files both read and write, branches both push to, APIs both define and consume). 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. 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.
How to use it
Reference it in AdaL, Claude Code, Cursor or any coding agent — nothing to install:
@skills cursor/principle-separate-before-serializing-shared-state