fix race when closing channel

balancer_wrapper.go

@@ -262,7 +262,7 @@ type acBalancerWrapper struct {
 
 // updateState is invoked by grpc to push a subConn state update to the
 // underlying balancer.
-func (acbw *acBalancerWrapper) updateState(s connectivity.State, curAddr resolver.Address, err error) {
+func (acbw *acBalancerWrapper) updateState(s connectivity.State, curAddr resolver.Address, err error, readyChan chan struct{}) {
 	acbw.ccb.serializer.TrySchedule(func(ctx context.Context) {
 		if ctx.Err() != nil || acbw.ccb.balancer == nil {
 			return
@@ -278,11 +278,11 @@ func (acbw *acBalancerWrapper) updateState(s connectivity.State, curAddr resolve
 		acbw.ac.mu.Lock()
 		defer acbw.ac.mu.Unlock()
 		if s == connectivity.Ready {
-			// When changing states to READY, reset stateReadyChan.  Wait until
+			// When changing states to READY, close stateReadyChan.  Wait until
 			// after we notify the LB policy's listener(s) in order to prevent
 			// ac.getTransport() from unblocking before the LB policy starts
 			// tracking the subchannel as READY.
-			close(acbw.ac.stateReadyChan)
+			close(readyChan)
 		}
 	})
 }

clientconn.go

@@ -1208,7 +1208,7 @@ func (ac *addrConn) updateConnectivityState(s connectivity.State, lastErr error)
 	} else {
 		channelz.Infof(logger, ac.channelz, "Subchannel Connectivity change to %v, last error: %s", s, lastErr)
 	}
-	ac.acbw.updateState(s, ac.curAddr, lastErr)
+	ac.acbw.updateState(s, ac.curAddr, lastErr, ac.stateReadyChan)
 }
 
 // adjustParams updates parameters used to create transports upon