Fix a data race in resolver_conn_wrapper.go (#3090)

dialoptions.go

@@ -69,6 +69,10 @@ type dialOptions struct {
 	minConnectTimeout           func() time.Duration
 	defaultServiceConfig        *ServiceConfig // defaultServiceConfig is parsed from defaultServiceConfigRawJSON.
 	defaultServiceConfigRawJSON *string
+	// This is used by ccResolverWrapper to backoff between successive calls to
+	// resolver.ResolveNow(). The user will have no need to configure this, but
+	// we need to be able to configure this in tests.
+	resolveNowBackoff func(int) time.Duration
 }
 
 // DialOption configures how we set up the connection.
@@ -559,6 +563,7 @@ func defaultDialOptions() dialOptions {
 			WriteBufferSize: defaultWriteBufSize,
 			ReadBufferSize:  defaultReadBufSize,
 		},
+		resolveNowBackoff: internalbackoff.DefaultExponential.Backoff,
 	}
 }
 
@@ -572,3 +577,13 @@ func withMinConnectDeadline(f func() time.Duration) DialOption {
 		o.minConnectTimeout = f
 	})
 }
+
+// withResolveNowBackoff specifies the function that clientconn uses to backoff
+// between successive calls to resolver.ResolveNow().
+//
+// For testing purpose only.
+func withResolveNowBackoff(f func(int) time.Duration) DialOption {
+	return newFuncDialOption(func(o *dialOptions) {
+		o.resolveNowBackoff = f
+	})
+}