reduce allocations in switch

src/yggdrasil/switch.go

@@ -577,23 +577,28 @@ func (t *switchTable) start() error {
 	return nil
 }
 
+type closerInfo struct {
+	port switchPort
+	dist int
+}
+
 // Return a map of ports onto distance, keeping only ports closer to the destination than this node
 // If the map is empty (or nil), then no peer is closer
-func (t *switchTable) getCloser(dest []byte) map[switchPort]int {
+func (t *switchTable) getCloser(dest []byte) []closerInfo {
 	table := t.getTable()
 	myDist := table.self.dist(dest)
 	if myDist == 0 {
 		// Skip the iteration step if it's impossible to be closer
 		return nil
 	}
-	closer := make(map[switchPort]int, len(table.elems))
+	t.queues.closer = t.queues.closer[:0]
 	for _, info := range table.elems {
 		dist := info.locator.dist(dest)
 		if dist < myDist {
-			closer[info.port] = dist
+			t.queues.closer = append(t.queues.closer, closerInfo{info.port, dist})
 		}
 	}
-	return closer
+	return t.queues.closer
 }
 
 // Returns true if the peer is closer to the destination than ourself
@@ -656,9 +661,9 @@ func (t *switchTable) handleIn(packet []byte, idle map[switchPort]time.Time) boo
 	var bestDist int
 	var bestTime time.Time
 	ports := t.core.peers.getPorts()
-	for port, dist := range closer {
-		to := ports[port]
-		thisTime, isIdle := idle[port]
+	for _, cinfo := range closer {
+		to := ports[cinfo.port]
+		thisTime, isIdle := idle[cinfo.port]
 		var update bool
 		switch {
 		case to == nil:
@@ -667,9 +672,9 @@ func (t *switchTable) handleIn(packet []byte, idle map[switchPort]time.Time) boo
 			//nothing
 		case best == nil:
 			update = true
-		case dist < bestDist:
+		case cinfo.dist < bestDist:
 			update = true
-		case dist > bestDist:
+		case cinfo.dist > bestDist:
 			//nothing
 		case thisTime.Before(bestTime):
 			update = true
@@ -678,7 +683,7 @@ func (t *switchTable) handleIn(packet []byte, idle map[switchPort]time.Time) boo
 		}
 		if update {
 			best = to
-			bestDist = dist
+			bestDist = cinfo.dist
 			bestTime = thisTime
 		}
 	}
@@ -711,6 +716,7 @@ type switch_buffers struct {
 	size        uint64                   // Total size of all buffers, in bytes
 	maxbufs     int
 	maxsize     uint64
+	closer      []closerInfo // Scratch space
 }
 
 func (b *switch_buffers) cleanup(t *switchTable) {