Fix race reordering tracker tier

diff --git a/client.go b/client.go
index b3eb7d99b0dc548ba30193dc436fcba19770c08c..4a6837d33f9cb958060c3415aace6d35c292171e 100644 (file)
--- a/client.go
+++ b/client.go
@@ -1496,7 +1496,7 @@ func (me *Client) addTorrent(t *torrent) (err error) {
        }
        me.torrents[t.InfoHash] = t
        if !me.disableTrackers {
-               go me.announceTorrent(t)
+               go me.announceTorrentTrackers(t)
        }
        if me.dHT != nil {
                go me.announceTorrentDHT(t, true)
@@ -1614,7 +1614,8 @@ func (cl *Client) announceTorrentDHT(t *torrent, impliedPort bool) {
        }
 }
 
-func (cl *Client) announceTorrent(t *torrent) {
+// Announce torrent to its trackers.
+func (cl *Client) announceTorrentTrackers(t *torrent) {
        req := tracker.AnnounceRequest{
                Event:    tracker.Started,
                NumWant:  -1,
@@ -1624,10 +1625,10 @@ func (cl *Client) announceTorrent(t *torrent) {
        }
 newAnnounce:
        for cl.waitWantPeers(t) {
-               cl.mu.Lock()
+               cl.mu.RLock()
                req.Left = t.BytesLeft()
                trackers := t.Trackers
-               cl.mu.Unlock()
+               cl.mu.RUnlock()
                for _, tier := range trackers {
                        for trIndex, tr := range tier {
                                if err := tr.Connect(); err != nil {
@@ -1652,7 +1653,14 @@ newAnnounce:
                                } else {
                                        log.Printf("%s: %d new peers from %s", t, len(peers), tr)
                                }
+
+                               // If the trackers list hasn't been touched (a new array would
+                               // have been assigned), then float this tracker to the top of
+                               // the tier.
+                               cl.mu.Lock()
                                tier[0], tier[trIndex] = tier[trIndex], tier[0]
+                               cl.mu.Unlock()
+
                                time.Sleep(time.Second * time.Duration(resp.Interval))
                                req.Event = tracker.None
                                continue newAnnounce