[MeshSync] Fix data race on informer stores map

[singhharsh1708]

What's going on

Handler.stores — the per-GVR informer store set — gets replaced wholesale by startDiscovery on the discovery goroutine every time (re)discovery runs, and it's read on a different goroutine by handleInformerStoreRequest → listStoreObjects whenever Meshery Server asks for an informer-store. Those two run at the same time with nothing synchronizing them, so the field is read and written with no happens-before between them — a data race, and go test -race flags it. It's the same shape as the bug already fixed for the exec/log-stream sessions map.

What I changed

I put an RWMutex (storesMu) around the stores field. The wholesale swap now goes through replaceStores under the write lock, and reads go through snapshotStores, which copies the current store values under the read lock and hands those back — so the lock is never held across cache.Store.List(). listStoreObjects iterates snapshotStores() instead of the raw map.

Nothing exported changes — no API, wire format, CRD, or config. Access is read-mostly, which is why RWMutex, and the set of objects returned is exactly what it was before.

Testing

Added meshsync/stores_test.go. TestStoresConcurrentAccess runs 16 goroutines racing replace against snapshot; it passes under -race, and it reports the race if you remove the guard, so it actually catches the regression. There are also completeness and nil-map cases. go test --short ./... -race is green across all packages, and go vet / gofmt are clean.

Why send it on its own

It's a prerequisite for the periodic-reconciliation work (docs/design/fd5-periodic-reconciliation.md), which adds a timer-driven reconcile loop that would be the second concurrent reader of h.stores alongside the informer-store path. I'm keeping it separate so that feature builds on a race-free store instead of bundling the fix into it.

Summary by CodeRabbit

• Bug Fixes

  • Improved reliability when discovery updates resource stores while requests are being handled.
  • Prevented potential concurrency issues and failures when retrieving stored resources, including when no stores are available.

• Tests

  • Added coverage for concurrent store updates, complete store snapshots, and empty-store scenarios.

[gemini-code-assist]

Code Review

This pull request introduces thread-safe access to the 'stores' map in the 'Handler' struct by adding a 'sync.RWMutex' ('storesMu') and implementing 'replaceStores' and 'snapshotStores' helper methods. These changes prevent race conditions between the discovery goroutine, which updates the stores, and the request listener goroutine, which reads them. Additionally, a new test file 'meshsync/stores_test.go' has been added to verify concurrent access and correct snapshot behavior. I have no further feedback to provide.

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[coderabbitai]

📝 Walkthrough

Walkthrough

The handler now protects discovery store replacement with an RWMutex, snapshots stores before listing objects, and adds tests for concurrent access, complete snapshots, and nil store maps.

Changes

Store concurrency

Layer / File(s)	Summary
Store swap and snapshot path meshsync/meshsync.go, meshsync/discovery.go, meshsync/handlers.go	Handler adds storesMu; discovery replaces stores under a write lock, and list handling reads a copied store snapshot under a read lock.
Concurrency and snapshot validation meshsync/stores_test.go	Tests cover concurrent replacement and reads, complete snapshots, and nil-map snapshots.

Estimated code review effort: 3 (Moderate) | ~20 minutes

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely describes the main change: fixing a data race on the informer stores map.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[singhharsh1708]

Friendly ping on this — it's been open a couple of weeks and CI is green (DCO, CodeRabbit, triage all passing). It's a small change: guards the informer stores map with an RWMutex and adds a test that reproduces the original race and passes under -race. Happy to rebase or adjust anything if a maintainer has feedback whenever it reaches the queue. Thanks!