Fix race running and closing webtorrent tracker clients

webtorrent/tracker_client.go

@@ -106,9 +106,18 @@ func (tc *TrackerClient) doWebsocket() error {
 	return err
 }
 
-func (tc *TrackerClient) Run() error {
+// Finishes initialization and spawns the run routine, calling onStop when it completes with the
+// result. We don't let the caller just spawn the runner directly, since then we can race against
+// .Close to finish initialization.
+func (tc *TrackerClient) Start(onStop func(error)) {
 	tc.pingTicker = time.NewTicker(60 * time.Second)
 	tc.cond.L = &tc.mu
+	go func() {
+		onStop(tc.run())
+	}()
+}
+
+func (tc *TrackerClient) run() error {
 	tc.mu.Lock()
 	for !tc.closed {
 		tc.mu.Unlock()

wstracker.go

@@ -55,12 +55,11 @@ func (me *websocketTrackers) Get(url string) (*webtorrent.TrackerClient, func())
 				}),
 			},
 		}
-		go func() {
-			err := value.TrackerClient.Run()
+		value.TrackerClient.Start(func(err error) {
 			if err != nil {
 				me.Logger.Printf("error running tracker client for %q: %v", url, err)
 			}
-		}()
+		})
 		if me.clients == nil {
 			me.clients = make(map[string]*refCountedWebtorrentTrackerClient)
 		}