fix context cancel problem

compose.yaml

@@ -1,6 +1,6 @@
 services:
   cache-proxy:
-    image: 100.64.0.2/guochao/cache-proxy:20250206
+    image: 100.64.0.2/guochao/cache-proxy:20250207
     build: .
 
     pull_policy: always

server.go

@@ -420,14 +420,25 @@ func (server *Server) fastesUpstream(r *http.Request, lastModified time.Time) (r
 	updateOnce := &sync.Once{}
 	notModifiedCh := make(chan int, 1)
 	notModifiedOnce := &sync.Once{}
+
+	resultIdx = -1
+
 	wg := &sync.WaitGroup{}
 	wg.Add(len(server.Upstreams))
 
 	defer close(updateCh)
+	defer close(notModifiedCh)
+	defer func() {
+		for cancelIdx, cancel := range cancelFuncs {
+			if cancelIdx == resultIdx || cancel == nil {
+				continue
+			}
+			cancel()
+		}
+	}()
 	for idx := range server.Upstreams {
 		idx := idx
 		ctx, cancel := context.WithCancel(context.Background())
-		defer cancel()
 		cancelFuncs[idx] = cancel
 
 		logger := slog.With("upstreamIdx", idx)
@@ -470,13 +481,6 @@ func (server *Server) fastesUpstream(r *http.Request, lastModified time.Time) (r
 			updateOnce.Do(func() {
 				resultResponse, resultCh, resultErr = response, ch, err
 				updateCh <- idx
-
-				for cancelIdx, cancel := range cancelFuncs {
-					if cancelIdx == idx {
-						continue
-					}
-					cancel()
-				}
 			})
 
 			logger.Debug("voted update")
@@ -485,8 +489,6 @@ func (server *Server) fastesUpstream(r *http.Request, lastModified time.Time) (r
 
 	wg.Wait()
 
-	resultIdx = -1
-
 	select {
 	case idx := <-updateCh:
 		resultIdx = idx