Summary

LocatorCache::get_or_insert_with in crates/pet-core/src/cache.rs uses a double-check locking pattern (read lock → compute → write lock → check again). Two threads can both pass the initial read-lock check, both call the closure f(), and only one insertion wins. If f() has side effects, they execute twice.

Concrete Example

In crates/pet-conda/src/lib.rs (line ~400), the mamba manager discovery inside the closure calls reporter.report_manager. The CacheReporter de-duplicates the reporting, but the get_mamba_manager process-spawning still executes twice.

Impact

Minor performance concern — not a correctness issue. The duplicate spawning is benign but wasteful.

Proposed Fix

Consider either:

1. Accepting this as a known trade-off (add comment documenting it) since the double-check pattern avoids holding a write lock during computation
2. Using a more granular per-key locking mechanism if spawning cost becomes measurable