avoid goroutine leak

app/dns/nameserver.go

@@ -17,6 +17,8 @@ import (
 
 const (
 	DefaultTTL       = uint32(3600)
+	CleanupInterval  = time.Second * 120
+	CleanupThreshold = 512
 )
 
 type ARecord struct {
@@ -38,6 +40,7 @@ type UDPNameServer struct {
 	address     v2net.Destination
 	requests    map[uint16]*PendingRequest
 	udpServer   *hub.UDPServer
+	nextCleanup time.Time
 }
 
 func NewUDPNameServer(address v2net.Destination, dispatcher dispatcher.PacketDispatcher) *UDPNameServer {
@@ -46,14 +49,11 @@ func NewUDPNameServer(address v2net.Destination, dispatcher dispatcher.PacketDis
 		requests:  make(map[uint16]*PendingRequest),
 		udpServer: hub.NewUDPServer(dispatcher),
 	}
-	go s.Cleanup()
 	return s
 }
 
 // @Private
 func (this *UDPNameServer) Cleanup() {
-	for {
-		time.Sleep(time.Second * 60)
 	expiredRequests := make([]uint16, 0, 16)
 	now := time.Now()
 	this.Lock()
@@ -68,13 +68,17 @@ func (this *UDPNameServer) Cleanup() {
 	}
 	this.Unlock()
 	expiredRequests = nil
-	}
 }
 
 // @Private
 func (this *UDPNameServer) AssignUnusedID(response chan<- *ARecord) uint16 {
 	var id uint16
 	this.Lock()
+	if len(this.requests) > CleanupThreshold && this.nextCleanup.Before(time.Now()) {
+		this.nextCleanup = time.Now().Add(CleanupInterval)
+		go this.Cleanup()
+	}
+
 	for {
 		id = uint16(rand.Intn(65536))
 		if _, found := this.requests[id]; found {