Close UDP listener in udp_listener plugin

also adding waitgroups to udp_listener and statsd plugins to verify that
all goroutines have been cleaned up before Stop() exits.

closes #869

plugins/inputs/statsd/statsd.go

@@ -50,6 +50,7 @@ type Statsd struct {
 	UDPPacketSize int `toml:"udp_packet_size"`
 
 	sync.Mutex
+	wg sync.WaitGroup
 
 	// Channel for all incoming statsd packets
 	in   chan []byte
@@ -238,6 +239,7 @@ func (s *Statsd) Start(_ telegraf.Accumulator) error {
 	s.sets = make(map[string]cachedset)
 	s.timings = make(map[string]cachedtimings)
 
+	s.wg.Add(2)
 	// Start the UDP listener
 	go s.udpListen()
 	// Start the line parser
@@ -248,13 +250,13 @@ func (s *Statsd) Start(_ telegraf.Accumulator) error {
 
 // udpListen starts listening for udp packets on the configured port.
 func (s *Statsd) udpListen() error {
+	defer s.wg.Done()
 	var err error
 	address, _ := net.ResolveUDPAddr("udp", s.ServiceAddress)
 	s.listener, err = net.ListenUDP("udp", address)
 	if err != nil {
 		log.Fatalf("ERROR: ListenUDP - %s", err)
 	}
-	defer s.listener.Close()
 	log.Println("Statsd listener listening on: ", s.listener.LocalAddr().String())
 
 	for {
@@ -264,7 +266,7 @@ func (s *Statsd) udpListen() error {
 		default:
 			buf := make([]byte, s.UDPPacketSize)
 			n, _, err := s.listener.ReadFromUDP(buf)
-			if err != nil {
+			if err != nil && !strings.Contains(err.Error(), "closed network") {
 				log.Printf("ERROR READ: %s\n", err.Error())
 				continue
 			}
@@ -282,6 +284,7 @@ func (s *Statsd) udpListen() error {
 // packet into statsd strings and then calls parseStatsdLine, which parses a
 // single statsd metric into a struct.
 func (s *Statsd) parser() error {
+	defer s.wg.Done()
 	for {
 		select {
 		case <-s.done:
@@ -561,8 +564,9 @@ func (s *Statsd) Stop() {
 	s.Lock()
 	defer s.Unlock()
 	log.Println("Stopping the statsd service")
-	s.listener.Close()
 	close(s.done)
+	s.listener.Close()
+	s.wg.Wait()
 	close(s.in)
 }