udpmux: rwlock for muxer:routes map

add fast read path to fetch existing routes

intra/udpmux.go

@@ -62,7 +62,7 @@ type muxer struct {
  cb func() // muxer.stop() callback (in a new goroutine)
  vnd netstack.DemuxerFn // for new routes in netstack
 
- rmu sync.Mutex  // protects routes
+ rmu sync.RWMutex // protects routes
  routes map[netip.AddrPort]*demuxconn // remote addr -> demuxed conn
 
  dxconnWG *sync.WaitGroup // wait group for demuxed conns
@@ -104,7 +104,7 @@ func newMuxer(cid, pid string, conn net.PacketConn, vnd netstack.DemuxerFn, f fu
  mxconn: conn,
  stats: &stats{start: time.Now()},
  routes: make(map[netip.AddrPort]*demuxconn),
- rmu: sync.Mutex{},
+ rmu: sync.RWMutex{},
  dxconns: make(chan *demuxconn),
  doneCh: make(chan struct{}),
  dxconnWG: &sync.WaitGroup{},
@@ -124,7 +124,7 @@ func (x *muxer) awaiters() {
  log.D("udp: mux: %s awaiter: watching %s => %s", x.cid, c.laddr, c.raddr)
  x.dxconnWG.Add(1) // accept
  core.Gx("udpmux.vend.close", func() {
- <-c.closed
+ <-c.closed // conn closed
  x.unroute(c)
  x.dxconnWG.Done() // unaccept
  })
@@ -216,15 +216,25 @@ func (x *muxer) readers() {
  }
 }
 
-func (x *muxer) route(to netip.AddrPort) *demuxconn {
- x.rmu.Lock()
- defer x.rmu.Unlock()
+func (x *muxer) routeFast(to netip.AddrPort) *demuxconn {
+ x.rmu.RLock()
+ defer x.rmu.RUnlock()
+ return x.routes[to]
+}
 
+func (x *muxer) route(to netip.AddrPort) *demuxconn {
  if !to.IsValid() {
  log.W("udp: mux: %s route: invalid addr %s", x.cid, to)
  return nil
  }
 
+ if conn := x.routeFast(to); conn != nil {
+ return conn
+ }
+
+ x.rmu.Lock()
+ defer x.rmu.Unlock()
+
  conn := x.routes[to]
  if conn == nil {
  // new routes created here won't really exist in netstack if