Production static file serving now uses FileInfoCache by default
with a 2-second TTL in router.go, dramatically reducing os.Stat
syscalls for missing files and repeated paths.
Changes:
- Add negative cache support to FileInfoCache (caches 'not found' results)
- Introduce statWithCache() helper in StaticHandler for uniform caching
- Make FileInfoCache TTL configurable via SetTTL()
- Default cacheTTL=0 disables caching in NewStaticHandler (tests compat)
- router.go enables fileInfoCache with 2s TTL for all static handlers
Benchmark (repeated 404s):
No cache: ~2651 ns/op, 2225 B/op, 15 allocs/op
With cache: ~1505 ns/op, 1905 B/op, 12 allocs/op
Improvement: -43% latency, -14% allocations
This addresses the dominant allocation source in v0.4.0 profile
(os.statNolog at 74.95% of allocations).
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>
