GODRIVER-3107 Fix leaking rttMonitor.runHellos() routine. (mongodb#1587)

(cherry picked from commit 9648fe1)

Author: qingyang-hu

x/mongo/driver/topology/rtt_monitor.go

@@ -54,7 +54,6 @@ type rttMonitor struct {
 	cfg      *rttConfig
 	ctx      context.Context
 	cancelFn context.CancelFunc
-	started  bool
 }
 
 var _ driver.RTTMonitor = &rttMonitor{}
@@ -78,7 +77,6 @@ func (r *rttMonitor) connect() {
 	r.connMu.Lock()
 	defer r.connMu.Unlock()
 
-	r.started = true
 	r.closeWg.Add(1)
 
 	go func() {
@@ -92,10 +90,6 @@ func (r *rttMonitor) disconnect() {
 	r.connMu.Lock()
 	defer r.connMu.Unlock()
 
-	if !r.started {
-		return
-	}
-
 	r.cancelFn()
 
 	// Wait for the existing connection to complete.

x/mongo/driver/topology/server.go

@@ -125,6 +125,7 @@ type Server struct {
 
 	processErrorLock sync.Mutex
 	rttMonitor       *rttMonitor
+	monitorOnce      sync.Once
 }
 
 // updateTopologyCallback is a callback used to create a server that should be called when the parent Topology instance
@@ -285,10 +286,10 @@ func (s *Server) Disconnect(ctx context.Context) error {
 	close(s.done)
 	s.cancelCheck()
 
-	s.rttMonitor.disconnect()
 	s.pool.close(ctx)
 
 	s.closewg.Wait()
+	s.rttMonitor.disconnect()
 	atomic.StoreInt64(&s.state, serverDisconnected)
 
 	return nil
@@ -666,8 +667,8 @@ func (s *Server) update() {
 		transitionedFromNetworkError := desc.LastError != nil && unwrapConnectionError(desc.LastError) != nil &&
 			previousDescription.Kind != description.Unknown
 
-		if isStreamingEnabled(s) && isStreamable(s) && !s.rttMonitor.started {
-			s.rttMonitor.connect()
+		if isStreamingEnabled(s) && isStreamable(s) {
+			s.monitorOnce.Do(s.rttMonitor.connect)
 		}
 
 		if isStreamable(s) && (serverSupportsStreaming || connectionIsStreaming) || transitionedFromNetworkError {