server: optimize message broadcast+targeted send

This commit slightly optimizes the process of broadcasting a message to
a list of peers, and also sending a set of messages to a target peer.

When broadcasting a message to a set of target peers, we now launch a
goroutine for each send as to not block the ChannelRouter on an
individual send. When sending a set of messages to a target peer, we
now give up the mutex as soon as we’ve access the map, rather than
holding onto it until the sending is complete.

lnd_test.go

@@ -531,6 +531,7 @@ func testSingleHopInvoice(net *networkHarness, t *harnessTest) {
 
 	// With the invoice for Bob added, send a payment towards Alice paying
 	// to the above generated invoice.
+	time.Sleep(time.Millisecond * 500)
 	sendStream, err := net.Alice.SendPayment(ctxb)
 	if err != nil {
 		t.Fatalf("unable to create alice payment stream: %v", err)

rpcserver.go

@@ -1735,6 +1735,8 @@ func (r *rpcServer) GetNetworkInfo(context.Context, *lnrpc.NetworkInfoRequest) (
 		return nil, err
 	}
 
+	// TODO(roasbeef): graph diameter
+
 	// TODO(roasbeef): also add oldest channel?
 	//  * also add median channel size
 	return &lnrpc.NetworkInfo{

server.go

@@ -594,9 +594,11 @@ out:
 						continue
 					}
 
-					for _, msg := range bMsg.msgs {
+					go func() {
-						peer.queueMsg(msg, nil)
+						for _, msg := range bMsg.msgs {
-					}
+							peer.queueMsg(msg, nil)
+						}
+					}()
 				}
 				s.peersMtx.RUnlock()
 
@@ -624,11 +626,11 @@ out:
 					sMsg.errChan <- errors.New("peer not found")
 					return
 				}
+				s.peersMtx.RUnlock()
 
 				for _, msg := range sMsg.msgs {
 					targetPeer.queueMsg(msg, nil)
 				}
-				s.peersMtx.RUnlock()
 
 				sMsg.errChan <- nil
 			}()