server: fix bug preventing Serve from exiting when Listener is closed (#1765)

server.go

@@ -479,8 +479,12 @@ func (s *Server) Serve(lis net.Listener) error {
 	s.serveWG.Add(1)
 	defer func() {
 		s.serveWG.Done()
-		// Block until Stop or GracefulStop is ready for us to return.
+		select {
+		// Stop or GracefulStop called; block until done and return nil.
+		case <-s.quit:
 			<-s.done
+		default:
+		}
 	}()
 
 	s.lis[lis] = true
@@ -526,7 +530,6 @@ func (s *Server) Serve(lis net.Listener) error {
 			s.printf("done serving; Accept = %v", err)
 			s.mu.Unlock()
 
-			// If Stop or GracefulStop is called, return nil.
 			select {
 			case <-s.quit:
 				return nil

test/end2end_test.go

@@ -5771,3 +5771,51 @@ func testCompressorRegister(t *testing.T, e env) {
 		t.Fatalf("%v.Recv() = %v, want <nil>", stream, err)
 	}
 }
+
+func TestServeExitsWhenListenerClosed(t *testing.T) {
+	defer leakcheck.Check(t)
+
+	ss := &stubServer{
+		emptyCall: func(context.Context, *testpb.Empty) (*testpb.Empty, error) {
+			return &testpb.Empty{}, nil
+		},
+	}
+
+	s := grpc.NewServer()
+	testpb.RegisterTestServiceServer(s, ss)
+
+	lis, err := net.Listen("tcp", "localhost:0")
+	if err != nil {
+		t.Fatalf("Failed to create listener: %v", err)
+	}
+
+	done := make(chan struct{})
+	go func() {
+		s.Serve(lis)
+		close(done)
+	}()
+
+	cc, err := grpc.Dial(lis.Addr().String(), grpc.WithInsecure(), grpc.WithBlock())
+	if err != nil {
+		t.Fatalf("Failed to dial server: %v", err)
+	}
+	defer cc.Close()
+	c := testpb.NewTestServiceClient(cc)
+	ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
+	defer cancel()
+	if _, err := c.EmptyCall(ctx, &testpb.Empty{}); err != nil {
+		t.Fatalf("Failed to send test RPC to server: %v", err)
+	}
+
+	if err := lis.Close(); err != nil {
+		t.Fatalf("Failed to close listener: %v", err)
+	}
+	const timeout = 5 * time.Second
+	timer := time.NewTimer(timeout)
+	select {
+	case <-done:
+		return
+	case <-timer.C:
+		t.Fatalf("Serve did not return after %v", timeout)
+	}
+}