add Notify API; move the name resolving into Balancer

balancer.go

@@ -37,6 +37,8 @@ import (
 	"sync"
 
 	"golang.org/x/net/context"
+	"google.golang.org/grpc/grpclog"
+	"google.golang.org/grpc/naming"
 	"google.golang.org/grpc/transport"
 )
 
@@ -53,6 +55,10 @@ type Address struct {
 // Balancer chooses network addresses for RPCs.
 // This is the EXPERIMENTAL API and may be changed or extended in the future.
 type Balancer interface {
+	// Start does the initialization work to bootstrap a Balancer. For example,
+	// this function may start the service discovery and watch the name resolution
+	// updates.
+	Start(target string) error
 	// Up informs the balancer that gRPC has a connection to the server at
 	// addr. It returns down which is called once the connection to addr gets
 	// lost or closed. Once down is called, addr may no longer be returned
@@ -64,21 +70,101 @@ type Balancer interface {
 	// is called once the rpc has completed or failed. put can collect and
 	// report rpc stats to remote load balancer.
 	Get(ctx context.Context) (addr Address, put func(), err error)
+	// Notify gRPC internals the list of Address which should be connected. gRPC
+	// internals will compare it with the exisiting connected addresses. If the
+	// address Balancer notified is not in the list of the connected addresses,
+	// gRPC starts to connect the address. If an address in the connected
+	// addresses is not in the notification list, the corresponding connect will be
+	// shutdown gracefully. Otherwise, there are no operations. Note that this
+	// function must return the full list of the Addrresses which should be connected.
+	// It is NOT delta.
+	Notify() <-chan []Address
 	// Close shuts down the balancer.
 	Close() error
 }
 
-// RoundRobin returns a Balancer that selects addresses round-robin.
+// RoundRobin returns a Balancer that selects addresses round-robin. It starts to watch
-func RoundRobin() Balancer {
+// the name resolution updates.
-	return &roundRobin{}
+func RoundRobin(r naming.Resolver) Balancer {
+	return &roundRobin{r: r}
 }
 
 type roundRobin struct {
-	mu     sync.Mutex
+	r         naming.Resolver
-	addrs  []Address
+	open      []Address // all the known addresses the client can potentially connect
-	next   int           // index of the next address to return for Get()
+	mu        sync.Mutex
-	waitCh chan struct{} // channel to block when there is no address available
+	addrCh    chan []Address // the channel to notify gRPC internals the list of addresses the client should connect to.
-	done   bool          // The Balancer is closed.
+	connected []Address      // all the connected addresses
+	next      int            // index of the next address to return for Get()
+	waitCh    chan struct{}  // the channel to block when there is no connected address available
+	done      bool           // The Balancer is closed.
+}
+
+func (rr *roundRobin) watchAddrUpdates(w naming.Watcher) error {
+	updates, err := w.Next()
+	if err != nil {
+		return err
+	}
+	for _, update := range updates {
+		addr := Address{
+			Addr:     update.Addr,
+			Metadata: update.Metadata,
+		}
+		switch update.Op {
+		case naming.Add:
+			var exisit bool
+			for _, v := range rr.open {
+				if addr == v {
+					exisit = true
+					grpclog.Println("grpc: The name resolver wanted to add an existing address: ", addr)
+					break
+				}
+			}
+			if exisit {
+				continue
+			}
+			rr.open = append(rr.open, addr)
+		case naming.Delete:
+			for i, v := range rr.open {
+				if v == addr {
+					copy(rr.open[i:], rr.open[i+1:])
+					rr.open = rr.open[:len(rr.open)-1]
+					break
+				}
+			}
+		default:
+			grpclog.Println("Unknown update.Op ", update.Op)
+		}
+	}
+	// Make a copy of rr.open and write it onto rr.addrCh so that gRPC internals gets notified.
+	open := make([]Address, len(rr.open))
+	rr.mu.Lock()
+	defer rr.mu.Unlock()
+	copy(open, rr.open)
+	if rr.done {
+		return ErrClientConnClosing
+	}
+	rr.addrCh <- open
+	return nil
+}
+
+func (rr *roundRobin) Start(target string) error {
+	if rr.r == nil {
+		return nil
+	}
+	w, err := rr.r.Resolve(target)
+	if err != nil {
+		return err
+	}
+	rr.addrCh = make(chan []Address)
+	go func() {
+		for {
+			if err := rr.watchAddrUpdates(w); err != nil {
+				return
+			}
+		}
+	}()
+	return nil
 }
 
 // Up appends addr to the end of rr.addrs and sends notification if there
@@ -86,13 +172,13 @@ type roundRobin struct {
 func (rr *roundRobin) Up(addr Address) func(error) {
 	rr.mu.Lock()
 	defer rr.mu.Unlock()
-	for _, a := range rr.addrs {
+	for _, a := range rr.connected {
 		if a == addr {
 			return nil
 		}
 	}
-	rr.addrs = append(rr.addrs, addr)
+	rr.connected = append(rr.connected, addr)
-	if len(rr.addrs) == 1 {
+	if len(rr.connected) == 1 {
 		// addr is only one available. Notify the Get() callers who are blocking.
 		if rr.waitCh != nil {
 			close(rr.waitCh)
@@ -108,10 +194,10 @@ func (rr *roundRobin) Up(addr Address) func(error) {
 func (rr *roundRobin) down(addr Address, err error) {
 	rr.mu.Lock()
 	defer rr.mu.Unlock()
-	for i, a := range rr.addrs {
+	for i, a := range rr.connected {
 		if a == addr {
-			copy(rr.addrs[i:], rr.addrs[i+1:])
+			copy(rr.connected[i:], rr.connected[i+1:])
-			rr.addrs = rr.addrs[:len(rr.addrs)-1]
+			rr.connected = rr.connected[:len(rr.connected)-1]
 			return
 		}
 	}
@@ -126,16 +212,13 @@ func (rr *roundRobin) Get(ctx context.Context) (addr Address, put func(), err er
 		err = ErrClientConnClosing
 		return
 	}
-	if rr.next >= len(rr.addrs) {
+	if rr.next >= len(rr.connected) {
 		rr.next = 0
 	}
-	if len(rr.addrs) > 0 {
+	if len(rr.connected) > 0 {
-		addr = rr.addrs[rr.next]
+		addr = rr.connected[rr.next]
 		rr.next++
 		rr.mu.Unlock()
-		put = func() {
-			rr.put(ctx, addr)
-		}
 		return
 	}
 	// There is no address available. Wait on rr.waitCh.
@@ -158,26 +241,24 @@ func (rr *roundRobin) Get(ctx context.Context) (addr Address, put func(), err er
 				err = ErrClientConnClosing
 				return
 			}
-			if len(rr.addrs) == 0 {
+			if len(rr.connected) == 0 {
 				// The newly added addr got removed by Down() again.
 				rr.mu.Unlock()
 				continue
 			}
-			if rr.next >= len(rr.addrs) {
+			if rr.next >= len(rr.connected) {
 				rr.next = 0
 			}
-			addr = rr.addrs[rr.next]
+			addr = rr.connected[rr.next]
 			rr.next++
 			rr.mu.Unlock()
-			put = func() {
-				rr.put(ctx, addr)
-			}
 			return
 		}
 	}
 }
 
-func (rr *roundRobin) put(ctx context.Context, addr Address) {
+func (rr *roundRobin) Notify() <-chan []Address {
+	return rr.addrCh
 }
 
 func (rr *roundRobin) Close() error {
@@ -188,5 +269,8 @@ func (rr *roundRobin) Close() error {
 		close(rr.waitCh)
 		rr.waitCh = nil
 	}
+	if rr.addrCh != nil {
+		close(rr.addrCh)
+	}
 	return nil
 }

balancer_test.go

@@ -122,7 +122,7 @@ func TestNameDiscovery(t *testing.T) {
 	// Start 2 servers on 2 ports.
 	numServers := 2
 	servers, r := startServers(t, numServers, math.MaxUint32)
-	cc, err := Dial("foo.bar.com", WithNameResolver(r), WithBlock(), WithInsecure(), WithCodec(testCodec{}))
+	cc, err := Dial("foo.bar.com", WithBalancer(RoundRobin(r)), WithBlock(), WithInsecure(), WithCodec(testCodec{}))
 	if err != nil {
 		t.Fatalf("Failed to create ClientConn: %v", err)
 	}
@@ -157,7 +157,7 @@ func TestNameDiscovery(t *testing.T) {
 
 func TestEmptyAddrs(t *testing.T) {
 	servers, r := startServers(t, 1, math.MaxUint32)
-	cc, err := Dial("foo.bar.com", WithNameResolver(r), WithBlock(), WithInsecure(), WithCodec(testCodec{}))
+	cc, err := Dial("foo.bar.com", WithBalancer(RoundRobin(r)), WithBlock(), WithInsecure(), WithCodec(testCodec{}))
 	if err != nil {
 		t.Fatalf("Failed to create ClientConn: %v", err)
 	}
@@ -167,12 +167,11 @@ func TestEmptyAddrs(t *testing.T) {
 	}
 	// Inject name resolution change to remove the server so that there is no address
 	// available after that.
-	var updates []*naming.Update
+	u := &naming.Update{
-	updates = append(updates, &naming.Update{
 		Op:   naming.Delete,
 		Addr: "127.0.0.1:" + servers[0].port,
-	})
+	}
-	r.w.inject(updates)
+	r.w.inject([]*naming.Update{u})
 	// Loop until the above updates apply.
 	for {
 		time.Sleep(10 * time.Millisecond)
@@ -189,24 +188,32 @@ func TestRoundRobin(t *testing.T) {
 	// Start 3 servers on 3 ports.
 	numServers := 3
 	servers, r := startServers(t, numServers, math.MaxUint32)
-	cc, err := Dial("foo.bar.com", WithNameResolver(r), WithBlock(), WithInsecure(), WithCodec(testCodec{}))
+	cc, err := Dial("foo.bar.com", WithBalancer(RoundRobin(r)), WithBlock(), WithInsecure(), WithCodec(testCodec{}))
 	if err != nil {
 		t.Fatalf("Failed to create ClientConn: %v", err)
 	}
-	// Add servers[1] and servers[2] to the service discovery.
+	// Add servers[1] to the service discovery.
-	var updates []*naming.Update
+	u := &naming.Update{
-	updates = append(updates, &naming.Update{
 		Op:   naming.Add,
 		Addr: "127.0.0.1:" + servers[1].port,
-	})
+	}
-	updates = append(updates, &naming.Update{
+	r.w.inject([]*naming.Update{u})
-		Op:   naming.Add,
-		Addr: "127.0.0.1:" + servers[2].port,
-	})
-	r.w.inject(updates)
 	req := "port"
 	var reply string
-	// Loop until an RPC is completed by servers[2].
+	// Loop until servers[1] is up
+	for {
+		if err := Invoke(context.Background(), "/foo/bar", &req, &reply, cc); err != nil && ErrorDesc(err) == servers[1].port {
+			break
+		}
+		time.Sleep(10 * time.Millisecond)
+	}
+	// Add server2[2] to the service discovery.
+	u = &naming.Update{
+		Op:   naming.Add,
+		Addr: "127.0.0.1:" + servers[2].port,
+	}
+	r.w.inject([]*naming.Update{u})
+	// Loop until both servers[2] are up.
 	for {
 		if err := Invoke(context.Background(), "/foo/bar", &req, &reply, cc); err != nil && ErrorDesc(err) == servers[2].port {
 			break
@@ -216,7 +223,7 @@ func TestRoundRobin(t *testing.T) {
 	// Check the incoming RPCs served in a round-robin manner.
 	for i := 0; i < 10; i++ {
 		if err := Invoke(context.Background(), "/foo/bar", &req, &reply, cc); err == nil || ErrorDesc(err) != servers[i%numServers].port {
-			t.Fatalf("Invoke(_, _, _, _, _) = %v, want %s", err, servers[i%numServers].port)
+			t.Fatalf("Index %d: Invoke(_, _, _, _, _) = %v, want %s", i, err, servers[i%numServers].port)
 		}
 	}
 	cc.Close()
@@ -227,7 +234,7 @@ func TestRoundRobin(t *testing.T) {
 
 func TestCloseWithPendingRPC(t *testing.T) {
 	servers, r := startServers(t, 1, math.MaxUint32)
-	cc, err := Dial("foo.bar.com", WithNameResolver(r), WithBlock(), WithInsecure(), WithCodec(testCodec{}))
+	cc, err := Dial("foo.bar.com", WithBalancer(RoundRobin(r)), WithBlock(), WithInsecure(), WithCodec(testCodec{}))
 	if err != nil {
 		t.Fatalf("Failed to create ClientConn: %v", err)
 	}
@@ -275,7 +282,7 @@ func TestCloseWithPendingRPC(t *testing.T) {
 
 func TestGetOnWaitChannel(t *testing.T) {
 	servers, r := startServers(t, 1, math.MaxUint32)
-	cc, err := Dial("foo.bar.com", WithNameResolver(r), WithBlock(), WithInsecure(), WithCodec(testCodec{}))
+	cc, err := Dial("foo.bar.com", WithBalancer(RoundRobin(r)), WithBlock(), WithInsecure(), WithCodec(testCodec{}))
 	if err != nil {
 		t.Fatalf("Failed to create ClientConn: %v", err)
 	}

call.go

@@ -169,7 +169,10 @@ func Invoke(ctx context.Context, method string, args, reply interface{}, cc *Cli
 		}
 		stream, err = sendRequest(ctx, cc.dopts.codec, cc.dopts.cp, callHdr, t, args, topts)
 		if err != nil {
-			put()
+			if put != nil {
+				put()
+				put = nil
+			}
 			if _, ok := err.(transport.ConnectionError); ok {
 				if c.failFast {
 					return toRPCErr(err)
@@ -181,7 +184,9 @@ func Invoke(ctx context.Context, method string, args, reply interface{}, cc *Cli
 		// Receive the response
 		err = recvResponse(cc.dopts, t, &c, stream, reply)
 		if err != nil {
-			put()
+			if put != nil {
+				put()
+			}
 			if _, ok := err.(transport.ConnectionError); ok {
 				if c.failFast {
 					return toRPCErr(err)
@@ -195,7 +200,10 @@ func Invoke(ctx context.Context, method string, args, reply interface{}, cc *Cli
 			c.traceInfo.tr.LazyLog(&payload{sent: false, msg: reply}, true)
 		}
 		t.CloseStream(stream, nil)
-		put()
+		if put != nil {
+			put()
+			put = nil
+		}
 		return Errorf(stream.StatusCode(), "%s", stream.StatusDesc())
 	}
 }

clientconn.go

@@ -65,12 +65,12 @@ var (
 	// ErrClientConnTimeout indicates that the connection could not be
 	// established or re-established within the specified timeout.
 	ErrClientConnTimeout = errors.New("grpc: timed out trying to connect")
-
+	// ErrNetworkIP indicates that the connection is down due to some network I/O error.
-	// errNetworkIP indicates that the connection is down due to some network I/O error.
+	ErrNetworkIO = errors.New("grpc: failed with network I/O error")
-	errNetworkIO = errors.New("grpc: failed with network I/O error")
+	// ErrConnDrain indicates that the connection starts to be drained and does not accept any new RPCs.
-	// errConnDrain indicates that the connection starts to be drained and does not accept any new RPCs.
+	ErrConnDrain = errors.New("grpc: the connection is drained")
-	errConnDrain   = errors.New("grpc: the connection is drained")
+	// ErrConnClosing
-	errConnClosing = errors.New("grpc: the addrConn is closing")
+	ErrConnClosing = errors.New("grpc: the addrConn is closing")
 	// minimum time to give a connection to complete
 	minConnectTimeout = 20 * time.Second
 )
@@ -82,7 +82,6 @@ type dialOptions struct {
 	cp       Compressor
 	dc       Decompressor
 	bs       backoffStrategy
-	resolver naming.Resolver
 	balancer Balancer
 	block    bool
 	insecure bool
@@ -115,13 +114,6 @@ func WithDecompressor(dc Decompressor) DialOption {
 	}
 }
 
-// WithNameResolver returns a DialOption which sets a name resolver for service discovery.
-func WithNameResolver(r naming.Resolver) DialOption {
-	return func(o *dialOptions) {
-		o.resolver = r
-	}
-}
-
 // WithBalancer returns a DialOption which sets a load balancer.
 func WithBalancer(b Balancer) DialOption {
 	return func(o *dialOptions) {
@@ -231,34 +223,29 @@ func Dial(target string, opts ...DialOption) (*ClientConn, error) {
 
 	cc.balancer = cc.dopts.balancer
 	if cc.balancer == nil {
-		cc.balancer = RoundRobin()
+		cc.balancer = RoundRobin(nil)
 	}
-
+	if err := cc.balancer.Start(target); err != nil {
-	if cc.dopts.resolver == nil {
+		return nil, err
-		addr := Address{
+	}
-			Addr: cc.target,
+	ch := cc.balancer.Notify()
-		}
+	if ch == nil {
-		if err := cc.newAddrConn(addr); err != nil {
+		// There is no name resolver installed.
+		addr := Address{Addr: target}
+		if err := cc.newAddrConn(addr, false); err != nil {
 			return nil, err
 		}
 	} else {
-		w, err := cc.dopts.resolver.Resolve(cc.target)
+		addrs, ok := <-ch
-		if err != nil {
+		if !ok || len(addrs) == 0 {
-			return nil, err
+			return nil, fmt.Errorf("grpc: there is no address available to dial")
 		}
-		cc.watcher = w
+		for _, a := range addrs {
-		// Get the initial name resolution and dial the first connection.
+			if err := cc.newAddrConn(a, false); err != nil {
-		if err := cc.watchAddrUpdates(); err != nil {
+				return nil, err
-			return nil, err
-		}
-		// Start a goroutine to watch for the future name resolution changes.
-		go func() {
-			for {
-				if err := cc.watchAddrUpdates(); err != nil {
-					return
-				}
 			}
-		}()
+		}
+		go cc.controller()
 	}
 
 	colonPos := strings.LastIndex(target, ":")
@@ -314,50 +301,48 @@ type ClientConn struct {
 	conns map[Address]*addrConn
 }
 
-func (cc *ClientConn) watchAddrUpdates() error {
+func (cc *ClientConn) controller() {
-	updates, err := cc.watcher.Next()
+	for {
-	if err != nil {
+		addrs, ok := <-cc.balancer.Notify()
-		return err
+		if !ok {
-	}
+			// cc has been closed.
-	for _, update := range updates {
+			return
-		switch update.Op {
+		}
-		case naming.Add:
+		var (
-			cc.mu.RLock()
+			add []Address   // Addresses need to setup connections.
-			addr := Address{
+			del []*addrConn // Connections need to tear down.
-				Addr:     update.Addr,
+		)
-				Metadata: update.Metadata,
+		cc.mu.Lock()
+		for _, a := range addrs {
+			if _, ok := cc.conns[a]; !ok {
+				add = append(add, a)
 			}
-			if _, ok := cc.conns[addr]; ok {
+		}
-				cc.mu.RUnlock()
+		for k, c := range cc.conns {
-				grpclog.Println("grpc: The name resolver wanted to add an existing address: ", addr)
+			var keep bool
-				continue
+			for _, a := range addrs {
+				if k == a {
+					keep = true
+					break
+				}
 			}
-			cc.mu.RUnlock()
+			if !keep {
-			if err := cc.newAddrConn(addr); err != nil {
+				del = append(del, c)
-				return err
 			}
-		case naming.Delete:
+		}
-			cc.mu.RLock()
+		cc.mu.Unlock()
-			addr := Address{
+		for _, a := range addrs {
-				Addr:     update.Addr,
+			if err := cc.newAddrConn(a, true); err != nil {
-				Metadata: update.Metadata,
+
 			}
-			ac, ok := cc.conns[addr]
+		}
-			if !ok {
+		for _, c := range del {
-				cc.mu.RUnlock()
+			c.tearDown(ErrConnDrain)
-				grpclog.Println("grpc: The name resolver wanted to delete a non-exist address: ", addr)
-				continue
-			}
-			cc.mu.RUnlock()
-			ac.tearDown(errConnDrain)
-		default:
-			grpclog.Println("Unknown update.Op ", update.Op)
 		}
 	}
-	return nil
 }
 
-func (cc *ClientConn) newAddrConn(addr Address) error {
+func (cc *ClientConn) newAddrConn(addr Address, skipWait bool) error {
 	ac := &addrConn{
 		cc:           cc,
 		addr:         addr,
@@ -394,7 +379,8 @@ func (cc *ClientConn) newAddrConn(addr Address) error {
 	ac.cc.mu.Unlock()
 
 	ac.stateCV = sync.NewCond(&ac.mu)
-	if ac.dopts.block {
+	// skipWait may overwrite the decision in ac.dopts.block.
+	if ac.dopts.block && !skipWait {
 		if err := ac.resetTransport(false); err != nil {
 			ac.tearDown(err)
 			return err
@@ -428,12 +414,16 @@ func (cc *ClientConn) getTransport(ctx context.Context) (transport.ClientTranspo
 	ac, ok := cc.conns[addr]
 	cc.mu.RUnlock()
 	if !ok {
-		put()
+		if put != nil {
+			put()
+		}
 		return nil, nil, transport.StreamErrorf(codes.Internal, "grpc: failed to find the transport to send the rpc")
 	}
 	t, err := ac.wait(ctx)
 	if err != nil {
-		put()
+		if put != nil {
+			put()
+		}
 		return nil, nil, err
 	}
 	return t, put, nil
@@ -538,10 +528,10 @@ func (ac *addrConn) resetTransport(closeTransport bool) error {
 		if ac.state == Shutdown {
 			// ac.tearDown(...) has been invoked.
 			ac.mu.Unlock()
-			return errConnClosing
+			return ErrConnClosing
 		}
 		if ac.down != nil {
-			ac.down(errNetworkIO)
+			ac.down(ErrNetworkIO)
 			ac.down = nil
 		}
 		ac.state = Connecting
@@ -579,7 +569,7 @@ func (ac *addrConn) resetTransport(closeTransport bool) error {
 			if ac.state == Shutdown {
 				// ac.tearDown(...) has been invoked.
 				ac.mu.Unlock()
-				return errConnClosing
+				return ErrConnClosing
 			}
 			ac.errorf("transient failure: %v", err)
 			ac.state = TransientFailure
@@ -616,7 +606,7 @@ func (ac *addrConn) resetTransport(closeTransport bool) error {
 			// ac.tearDown(...) has been invoked.
 			ac.mu.Unlock()
 			newTransport.Close()
-			return errConnClosing
+			return ErrConnClosing
 		}
 		ac.state = Ready
 		ac.stateCV.Broadcast()
@@ -671,7 +661,7 @@ func (ac *addrConn) wait(ctx context.Context) (transport.ClientTransport, error)
 		switch {
 		case ac.state == Shutdown:
 			ac.mu.Unlock()
-			return nil, errConnClosing
+			return nil, ErrConnClosing
 		case ac.state == Ready:
 			ct := ac.transport
 			ac.mu.Unlock()
@@ -725,7 +715,7 @@ func (ac *addrConn) tearDown(err error) {
 		ac.ready = nil
 	}
 	if ac.transport != nil {
-		if err == errConnDrain {
+		if err == ErrConnDrain {
 			ac.transport.GracefulClose()
 		} else {
 			ac.transport.Close()