Frontend Asset Optimization

[akshayutture-augment]

Test 8

Summary by CodeRabbit

• Refactor
  • Improved internal performance and stability of web asset handling through enhanced thread-safety mechanisms.

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Replicated from ai-code-review-evaluation/grafana-coderabbit#8

[akshayutture-augment]

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Walkthrough

The web assets caching mechanism in pkg/api/webassets/webassets.go has been enhanced with thread-safety using a read-write mutex. The global cache variable is now guarded by sync.RWMutex, with cache reads protected by read locks and updates protected by write locks, maintaining existing behavior while preventing concurrent access issues.

Changes

Cohort / File(s)	Summary
Thread-safe web assets cache pkg/api/webassets/webassets.go	Added sync.RWMutex for cache synchronization; replaced single cache variable with mutex-guarded pair (entryPointAssetsCacheMu, entryPointAssetsCache); updated GetWebAssets to use read lock for cache reads and write lock for cache updates.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

• Verify correct lock placement and duration—ensure read locks are held only during reads and write locks only during updates
• Check for potential deadlock scenarios and lock ordering
• Confirm RWMutex is the appropriate synchronization primitive for this access pattern

Poem

🐰 A mutex guards the cache with care,
Threads no longer cause despair,
Readers hop with locks so light,
Writers ensure updates are right,
Web assets flow, synchronized and fair!

Pre-merge checks and finishing touches

❌ Failed checks (1 warning, 1 inconclusive)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	You can run @coderabbitai generate docstrings to improve docstring coverage.
Title check	❓ Inconclusive	The title 'Frontend Asset Optimization' is vague and generic, lacking specificity about the actual changes made in this pull request.	Consider a more specific title that reflects the main change, such as 'Add thread-safe locking to web assets cache' or 'Synchronize access to entryPointAssetsCache with mutex'.

✅ Passed checks (1 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.

✨ Finishing touches

• 📝 Generate docstrings

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch asset-loading-optimized

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Actionable comments posted: 1

📜 Review details

Configuration used: CodeRabbit UI

Review profile: CHILL

Plan: Pro

📥 Commits

Reviewing files that changed from the base of the PR and between 0a870e6 and 95000f9.

📒 Files selected for processing (1)

• pkg/api/webassets/webassets.go (2 hunks)

🔇 Additional comments (3)

pkg/api/webassets/webassets.go (3)

11-11: LGTM!

The sync package import is necessary for the RWMutex used to guard the cache.

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35-38: LGTM!

The mutex and cache variable are properly declared and unexported. The TODO comment appropriately flags the global state as technical debt to address later.

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69-70: Verify error handling behavior.

The cache is updated even when err != nil, potentially setting it to nil or a partial result. While the early-return check on line 45 guards against returning a nil cache, verify that this error handling aligns with expectations and that downstream callers handle errors appropriately.

Note: This behavior appears to predate the mutex addition, but it's worth confirming during concurrent scenarios.

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⚠️ Potential issue | 🟠 Major

Incomplete double-checked locking pattern.

After releasing the read lock (line 43) and before acquiring the write lock (line 48), another goroutine may have already updated the cache. Without a second check after acquiring the write lock, multiple concurrent callers could redundantly perform the expensive asset-reading operation.

Apply this diff to complete the double-checked locking pattern:

 	entryPointAssetsCacheMu.Lock()
 	defer entryPointAssetsCacheMu.Unlock()
+
+	// Double-check: another goroutine may have updated the cache
+	if cfg.Env != setting.Dev && entryPointAssetsCache != nil {
+		return entryPointAssetsCache, nil
+	}

 	var err error

🤖 Prompt for AI Agents

In pkg/api/webassets/webassets.go around lines 41 to 49, the double-checked
locking is incomplete: after releasing the read lock and before acquiring the
write lock another goroutine may have populated entryPointAssetsCache. Update
the code to re-check entryPointAssetsCache after acquiring the write lock and if
it's now non-nil (and cfg.Env != setting.Dev) return it immediately; only
proceed with the expensive asset-reading and assignment when the cache is still
nil (or env requires reload). Ensure the write-lock is held while assigning
entryPointAssetsCache and that defer entryPointAssetsCacheMu.Unlock() remains in
place.