fix discovery resolver watch goroutine leak (#750)

* fix discovery resolver watch goroutine leak

cmd/protoc-gen-go-errors/go.sum

@@ -13,6 +13,7 @@ github.com/go-kratos/kratos/v2 v2.0.0-20210217083752-d86d233d93ce h1:LfOsLN9s8tA
 github.com/go-kratos/kratos/v2 v2.0.0-20210217083752-d86d233d93ce/go.mod h1:oLvFyDBJkkWN8TPqb+NmpvRrSy9uM/K+XQubVRc11a8=
 github.com/go-kratos/kratos/v2 v2.0.0-alpha4 h1:MKkkSZigSMg7Kx8HzrobZ93zlgmi0tAKWM9bMf6YTpU=
 github.com/go-kratos/kratos/v2 v2.0.0-alpha4/go.mod h1:oLvFyDBJkkWN8TPqb+NmpvRrSy9uM/K+XQubVRc11a8=
+github.com/go-kratos/kratos/v2 v2.0.0-alpha5/go.mod h1:oLvFyDBJkkWN8TPqb+NmpvRrSy9uM/K+XQubVRc11a8=
 github.com/golang/glog v0.0.0-20160126235308-23def4e6c14b/go.mod h1:SBH7ygxi8pfUlaOkMMuAQtPIUF8ecWP5IEl/CR7VP2Q=
 github.com/golang/mock v1.1.1/go.mod h1:oTYuIxOrZwtPieC+H1uAHpcLFnEyAGVDL/k47Jfbm0A=
 github.com/golang/protobuf v1.2.0/go.mod h1:6lQm79b+lXiMfvg/cZm0SGofjICqVBUtrP5yJMmIC1U=

transport/grpc/resolver/discovery/builder.go

@@ -42,10 +42,13 @@ func (d *builder) Build(target resolver.Target, cc resolver.ClientConn, opts res
 	if err != nil {
 		return nil, err
 	}
+	ctx, cancel := context.WithCancel(context.Background())
 	r := &discoveryResolver{
 		w:      w,
 		cc:     cc,
 		log:    log.NewHelper("grpc/resolver/discovery", d.logger),
+		ctx:    ctx,
+		cancel: cancel,
 	}
 	go r.watch()
 	return r, nil

transport/grpc/resolver/discovery/resolver.go

@@ -1,6 +1,7 @@
 package discovery
 
 import (
+	"context"
 	"net/url"
 	"time"
 
@@ -14,10 +15,20 @@ type discoveryResolver struct {
 	w   registry.Watcher
 	cc  resolver.ClientConn
 	log *log.Helper
+
+	ctx    context.Context
+	cancel context.CancelFunc
 }
 
 func (r *discoveryResolver) watch() {
 	for {
+		select {
+		case <-r.ctx.Done():
+			//goroutine exit
+			return
+		default:
+		}
+
 		ins, err := r.w.Next()
 		if err != nil {
 			r.log.Errorf("Failed to watch discovery endpoint: %v", err)
@@ -47,6 +58,7 @@ func (r *discoveryResolver) update(ins []*registry.ServiceInstance) {
 }
 
 func (r *discoveryResolver) Close() {
+	r.cancel()
 	r.w.Close()
 }
 

transport/grpc/resolver/discovery/resolver_test.go

@@ -0,0 +1,58 @@
+package discovery
+
+import (
+	"context"
+	"github.com/go-kratos/kratos/v2/log"
+	"github.com/go-kratos/kratos/v2/registry"
+	"google.golang.org/grpc/resolver"
+	"testing"
+	"time"
+)
+
+type testClientConn struct {
+	resolver.ClientConn // For unimplemented functions
+	te                  *testing.T
+}
+
+func (t *testClientConn) UpdateState(s resolver.State) {
+	t.te.Log("UpdateState", s)
+}
+
+type testWatch struct {
+}
+
+func (m *testWatch) Next() ([]*registry.ServiceInstance, error) {
+	time.Sleep(time.Millisecond * 200)
+	ins := []*registry.ServiceInstance{
+		&registry.ServiceInstance{
+			ID:      "mock_ID",
+			Name:    "mock_Name",
+			Version: "mock_Version",
+		},
+	}
+	return ins, nil
+}
+
+// Watch creates a watcher according to the service name.
+func (m *testWatch) Close() error {
+	return nil
+}
+
+func TestWatch(t *testing.T) {
+	ctx, cancel := context.WithCancel(context.Background())
+
+	r := &discoveryResolver{
+		w:      &testWatch{},
+		cc:     &testClientConn{te: t},
+		log:    log.NewHelper("grpc/resolver/discovery", log.DefaultLogger),
+		ctx:    ctx,
+		cancel: cancel,
+	}
+	go func() {
+		time.Sleep(time.Second * 2)
+		r.Close()
+	}()
+	r.watch()
+
+	t.Log("watch goroutine exited after 2 second")
+}