Allow multiple calls to ensureRecalculated() to wait on the same calc…

…ulation

If another call is already waiting, wait on the same chan.

This is an improvement on the previous behaviour that only allowed one
ensureRecalculated() to proceed per calculate(), in the presence of
many recalculate() requests.

It is now possible for a later call to overtake the first.  Previously
it was possible for a later call to overtake an earlier call except
for the first.

routes.go

@@ -19,7 +19,7 @@ type routes struct {
 	broadcast    broadcastRoutes
 	broadcastAll broadcastRoutes // [1]
 	recalc       chan<- *struct{}
-	wait         chan<- chan struct{}
+	wait         chan chan struct{}
 	action       chan<- func()
 	// [1] based on *all* connections, not just established &
 	// symmetric ones
@@ -167,7 +167,13 @@ func (r *routes) recalculate() {
 
 // EnsureRecalculated waits for any preceding Recalculate requests to finish.
 func (r *routes) ensureRecalculated() {
-	done := make(chan struct{})
+	var done chan struct{}
+	// If another call is already waiting, wait on the same chan, otherwise make a new one
+	select {
+	case done = <-r.wait:
+	default:
+		done = make(chan struct{})
+	}
 	r.wait <- done
 	<-done
 }