FileInfoCache.Get previously acquired TWO locks on every cache hit:
1. RLock → check existence + TTL
2. Release RLock → Lock → MoveToFront (LRU update) → Unlock
The MoveToFront on every hit forced a read-to-write lock upgrade,
creating contention under concurrent reads.
Apply approximate LRU: skip MoveToFront on Get (read) path entirely.
LRU position is only updated in Set (write) path. This is the same
pattern already used by internal/cache/file_cache.go.
Result: Get fast path reduced from 2 lock acquisitions to 1 RLock.
TTL-expired entries still use double-check locking for safe removal.
- Change FileInfoCache.mu from sync.Mutex to sync.RWMutex
- Get method uses RLock for concurrent read access
- Stats method uses RLock for read-only operation
- Double-check pattern for lock upgrades (TTL expiry, LRU move)
This improves concurrent read performance for the FileInfo cache,
which is read-heavy in static file serving scenarios.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
