Make half-open connection limit more dynamic

diff --git a/torrent.go b/torrent.go
index ffaedb3f03f6f8954ffd6debf278262bef3fbee2..007d35def278f15a56b03579a966b98d0d1c66c6 100644 (file)
--- a/torrent.go
+++ b/torrent.go
@@ -82,7 +82,8 @@ type Torrent struct {
        info  *metainfo.Info
        files *[]*File
 
-       // Active peer connections, running message stream loops.
+       // Active peer connections, running message stream loops. TODO: Make this
+       // open (not-closed) connections only.
        conns               map[*connection]struct{}
        maxEstablishedConns int
        // Set of addrs to which we're attempting to connect. Connections are
@@ -1054,13 +1055,32 @@ func (t *Torrent) pieceCompletionChanged(piece int) {
        t.updatePiecePriority(piece)
 }
 
+func (t *Torrent) numReceivedConns() (ret int) {
+       for c := range t.conns {
+               if c.Discovery == peerSourceIncoming {
+                       ret++
+               }
+       }
+       return
+}
+
+func (t *Torrent) maxHalfOpen() int {
+       // Note that if we somehow exceed the maximum established conns, we want
+       // the negative value to have an effect.
+       establishedHeadroom := int64(t.maxEstablishedConns - len(t.conns))
+       extraIncoming := int64(t.numReceivedConns() - t.maxEstablishedConns/2)
+       // We want to allow some experimentation with new peers, and to try to
+       // upset an oversupply of received connections.
+       return int(min(max(5, extraIncoming)+establishedHeadroom, int64(t.cl.halfOpenLimit)))
+}
+
 func (t *Torrent) openNewConns() {
        defer t.updateWantPeersEvent()
        for len(t.peers) != 0 {
                if !t.wantConns() {
                        return
                }
-               if len(t.halfOpen) >= t.cl.halfOpenLimit {
+               if len(t.halfOpen) >= t.maxHalfOpen() {
                        return
                }
                var (