feat: add Cache.Stop to shut down janitor without finalizer

cache.go

@@ -1087,18 +1087,43 @@ func (j *janitor) Run(c *cache) {
 }
 
 func stopJanitor(c *Cache) {
-	c.janitor.stop <- true
+	if c == nil || c.cache == nil || c.janitor == nil {
+		return
+	}
+	// Non-blocking send: Stop may already have closed the janitor.
+	select {
+	case c.janitor.stop <- true:
+	default:
+	}
+	c.janitor = nil
 }
 
 func runJanitor(c *cache, ci time.Duration) {
 	j := &janitor{
 		Interval: ci,
-		stop:     make(chan bool),
+		stop:     make(chan bool, 1),
 	}
 	c.janitor = j
 	go j.Run(c)
 }
 
+// Stop ends the background janitor goroutine, if one is running.
+// It is safe to call multiple times. After Stop, expired items are no longer
+// removed automatically; callers may still invoke DeleteExpired manually.
+//
+// Prefer Stop over relying solely on the finalizer when the cache is used in
+// tests (including testing/synctest) or short-lived processes that check for
+// goroutine leaks.
+func (c *Cache) Stop() {
+	if c == nil || c.cache == nil {
+		return
+	}
+	if c.janitor != nil {
+		stopJanitor(c)
+	}
+	runtime.SetFinalizer(c, nil)
+}
+
 func newCache(de time.Duration, m map[string]Item) *cache {
 	if de == 0 {
 		de = -1

cache_test.go

@@ -1769,3 +1769,23 @@ func TestGetWithExpiration(t *testing.T) {
 		t.Error("expiration for e is in the past")
 	}
 }
+
+
+func TestStopJanitor(t *testing.T) {
+	tc := New(DefaultExpiration, 50*time.Millisecond)
+	tc.Set("a", "b", DefaultExpiration)
+	tc.Stop()
+	// Second Stop must be a no-op.
+	tc.Stop()
+	// Cache remains usable after Stop.
+	tc.Set("c", "d", DefaultExpiration)
+	v, found := tc.Get("c")
+	if !found || v != "d" {
+		t.Fatalf("expected usable cache after Stop, got %v %v", v, found)
+	}
+}
+
+func TestStopWithoutJanitor(t *testing.T) {
+	tc := New(DefaultExpiration, 0)
+	tc.Stop() // no-op path
+}