fix deadlock of roundrobin balancer

balancer.go

@@ -144,14 +144,15 @@ type addrInfo struct {
 }
 
 type roundRobin struct {
-	r      naming.Resolver
-	w      naming.Watcher
-	addrs  []*addrInfo // all the addresses the client should potentially connect
-	mu     sync.Mutex
-	addrCh chan []Address // the channel to notify gRPC internals the list of addresses the client should connect to.
-	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.
+	r        naming.Resolver
+	w        naming.Watcher
+	addrs    []*addrInfo // all the addresses the client should potentially connect
+	mu       sync.Mutex
+	addrChMu sync.Mutex     // protects addrCh
+	addrCh   chan []Address // the channel to notify gRPC internals the list of addresses the client should connect to.
+	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() error {
@@ -160,8 +161,10 @@ func (rr *roundRobin) watchAddrUpdates() error {
 		grpclog.Printf("grpc: the naming watcher stops working due to %v.\n", err)
 		return err
 	}
+	rr.addrChMu.Lock()
+	defer rr.addrChMu.Unlock()
 	rr.mu.Lock()
-	defer rr.mu.Unlock()
+
 	for _, update := range updates {
 		addr := Address{
 			Addr:     update.Addr,
@@ -199,9 +202,15 @@ func (rr *roundRobin) watchAddrUpdates() error {
 		open[i] = v.addr
 	}
 	if rr.done {
+		rr.mu.Unlock()
 		return ErrClientConnClosing
 	}
-	rr.addrCh <- open
+	done := rr.done
+	rr.mu.Unlock()
+
+	if !done {
+		rr.addrCh <- open
+	}
 	return nil
 }
 
@@ -373,8 +382,11 @@ func (rr *roundRobin) Notify() <-chan []Address {
 }
 
 func (rr *roundRobin) Close() error {
+	rr.addrChMu.Lock()
+	defer rr.addrChMu.Unlock()
 	rr.mu.Lock()
 	defer rr.mu.Unlock()
+
 	if rr.done {
 		return errBalancerClosed
 	}