.

go/neo/connection.go

@@ -410,24 +410,34 @@ func (c *Conn) shutdownRX(errMsg *Error) {
 }
 
 // downRX marks .rxq as no longer operational.
+//
+// used in shutdownRX and separately to mark RX down for light Conns.
 func (c *Conn) downRX(errMsg *Error) {
+	// let serveRecv know RX is down for this connection
 	c.rxdownFlag.Set(1) // XXX cmpxchg and return if already down?
 
-	// dequeue all packets already queued in c.rxq
-	// (once serveRecv sees c.rxdownFlag it won't try to put new packets into
-	//  c.rxq, but something finite could be already there)
-	// XXX also describe race we avoid with rxdownFlag / rxqActive dance
+	// drain all packets from .rxq:
+	// - something could be already buffered there
+	// - serveRecv could start writing rxq at the same time we set rxdownFlag; we derace it.
 	i := 0
-loop:
 	for {
+		// we set .rxdownFlag=1 above.
+		// now if serveRecv is outside `.rxq <- ...` critical section we know it is either:
+		// - before it	-> it will eventually see .rxdownFlag=1 and wont send pkt ro rxq.
+		// - after it	-> it already sent pkt to rxq and won't touch
+		//		   rxq until next packet (where it will hit "before it").
+		//
+		// when serveRecv stopped sending we know we are done draining when rxq is empty.
+		if c.rxqActive.Get() == 0 && len(c.rxq) == 0 {
+			break
+		}
+
 		select {
 		case <-c.rxq:
 			i++
 
 		default:
-			if c.rxqActive.Get() == 0 && len(c.rxq) == 0 {
-				break loop
-			}
+			// ok - continue spinning
 		}
 	}
 
@@ -1204,32 +1214,6 @@ func (l *linkListener) Addr() net.Addr {
 	return l.l.Addr()
 }
 
-/*
-XXX do if this is needed in a second place besides talkMaster1
-// ---- Listen for single Conn over NodeLink use-cases ----
-
-// XXX
-func ListenSingleConn(link *NodeLink) ConnListener {
-	l := &listen1conn{link}
-	// XXX go ...
-	return l
-}
-
-// ConnListener XXX ...
-type ConnListener interface {
-	// XXX +Close, Addr ?
-
-	// Accept returns new connection multiplexed over NodeLink
-	Accept() (*Conn, error)
-}
-
-type listen1conn struct {
-	link *NodeLink
-}
-
-func ...
-*/
-
 
 // ---- for convenience: Conn -> NodeLink & local/remote link addresses  ----
 
@@ -1350,6 +1334,8 @@ func (c *Conn) Recv() (Msg, error) {
 // sendMsg sends message with specified connection ID.
 //
 // it encodes message int packet, sets header appropriately and sends it.
+//
+// it is ok to call sendMsg in parallel with serveSend running XXX why
 func (link *NodeLink) sendMsg(connId uint32, msg Msg) error {
 	traceMsgSendPre(link, connId, msg)