added stat cache

pkg/fs/stat.go

@@ -0,0 +1,64 @@
+// Copyright (C) 2022 Marius Schellenberger
+
+package fs
+
+import (
+	"context"
+	"os"
+	"sync"
+	"time"
+)
+
+const statExpiry = time.Minute * 5
+
+type statCacheEntry struct {
+	mtime time.Time
+	fi    os.FileInfo
+}
+
+type StatCache struct {
+	mu  sync.RWMutex
+	ctx context.Context
+	m   map[string]*statCacheEntry
+}
+
+func NewStatCache(ctx context.Context) *StatCache {
+	sc := &StatCache{ctx: ctx, m: make(map[string]*statCacheEntry)}
+	go sc.cleanup()
+	return sc
+}
+
+func (sc *StatCache) cleanup() {
+	t := time.NewTicker(statExpiry)
+	defer t.Stop()
+	for {
+		select {
+		case <-sc.ctx.Done():
+			return
+		case <-t.C:
+		}
+		sc.mu.Lock()
+		now := time.Now()
+		for k, sce := range sc.m {
+			if now.After(sce.mtime) {
+				delete(sc.m, k)
+			}
+		}
+		sc.mu.Unlock()
+	}
+}
+
+func (sc *StatCache) Get(name string) (os.FileInfo, error) {
+	sc.mu.RLock()
+	defer sc.mu.RUnlock()
+	if sce, ok := sc.m[name]; ok {
+		return sce.fi, nil
+	}
+	return nil, NoCacheEntry
+}
+
+func (sc *StatCache) Set(name string, fi os.FileInfo) {
+	sc.mu.Lock()
+	defer sc.mu.Unlock()
+	sc.m[name] = &statCacheEntry{time.Now().Add(statExpiry), fi}
+}