Use workers instead spawning goroutines for each incoming DNS request (#664)

* Use workers instead spawning goroutines for each incoming DNS request

* Replace count (int) with inUse (bool)

server.go

@@ -9,12 +9,19 @@ import (
 	"io"
 	"net"
 	"sync"
+	"sync/atomic"
 	"time"
 )
 
 // Maximum number of TCP queries before we close the socket.
 const maxTCPQueries = 128
 
+// Interval for stop worker if no load
+const idleWorkerTimeout = 10 * time.Second
+
+// Maximum number of workers
+const maxWorkersCount = 10000
+
 // Handler is implemented by any value that implements ServeDNS.
 type Handler interface {
 	ServeDNS(w ResponseWriter, r *Msg)
@@ -43,6 +50,7 @@ type ResponseWriter interface {
 }
 
 type response struct {
+	msg            []byte
 	hijacked       bool // connection has been hijacked by handler
 	tsigStatus     error
 	tsigTimersOnly bool
@@ -296,11 +304,60 @@ type Server struct {
 	// DecorateWriter is optional, allows customization of the process that writes raw DNS messages.
 	DecorateWriter DecorateWriter
 
+	// UDP packet or TCP connection queue
+	queue chan *response
+	// Workers count
+	workersCount int32
 	// Shutdown handling
 	lock    sync.RWMutex
 	started bool
 }
 
+func (srv *Server) worker(w *response) {
+	srv.serve(w)
+
+	for {
+		count := atomic.LoadInt32(&srv.workersCount)
+		if count > maxWorkersCount {
+			return
+		}
+		if atomic.CompareAndSwapInt32(&srv.workersCount, count, count+1) {
+			break
+		}
+	}
+
+	defer atomic.AddInt32(&srv.workersCount, -1)
+
+	inUse := false
+	timeout := time.NewTimer(idleWorkerTimeout)
+	defer timeout.Stop()
+LOOP:
+	for {
+		select {
+		case w, ok := <-srv.queue:
+			if !ok {
+				break LOOP
+			}
+			inUse = true
+			srv.serve(w)
+		case <-timeout.C:
+			if !inUse {
+				break LOOP
+			}
+			inUse = false
+			timeout.Reset(idleWorkerTimeout)
+		}
+	}
+}
+
+func (srv *Server) spawnWorker(w *response) {
+	select {
+	case srv.queue <- w:
+	default:
+		go srv.worker(w)
+	}
+}
+
 // ListenAndServe starts a nameserver on the configured address in *Server.
 func (srv *Server) ListenAndServe() error {
 	srv.lock.Lock()
@@ -308,6 +365,7 @@ func (srv *Server) ListenAndServe() error {
 	if srv.started {
 		return &Error{err: "server already started"}
 	}
+
 	addr := srv.Addr
 	if addr == "" {
 		addr = ":domain"
@@ -315,6 +373,8 @@ func (srv *Server) ListenAndServe() error {
 	if srv.UDPSize == 0 {
 		srv.UDPSize = MinMsgSize
 	}
+	srv.queue = make(chan *response)
+	defer close(srv.queue)
 	switch srv.Net {
 	case "tcp", "tcp4", "tcp6":
 		a, err := net.ResolveTCPAddr(srv.Net, addr)
@@ -379,8 +439,11 @@ func (srv *Server) ActivateAndServe() error {
 	if srv.started {
 		return &Error{err: "server already started"}
 	}
+
 	pConn := srv.PacketConn
 	l := srv.Listener
+	srv.queue = make(chan *response)
+	defer close(srv.queue)
 	if pConn != nil {
 		if srv.UDPSize == 0 {
 			srv.UDPSize = MinMsgSize
@@ -438,7 +501,6 @@ func (srv *Server) getReadTimeout() time.Duration {
 }
 
 // serveTCP starts a TCP listener for the server.
-// Each request is handled in a separate goroutine.
 func (srv *Server) serveTCP(l net.Listener) error {
 	defer l.Close()
 
@@ -446,11 +508,6 @@ func (srv *Server) serveTCP(l net.Listener) error {
 		srv.NotifyStartedFunc()
 	}
 
-	handler := srv.Handler
-	if handler == nil {
-		handler = DefaultServeMux
-	}
-	// deadline is not used here
 	for {
 		rw, err := l.Accept()
 		srv.lock.RLock()
@@ -465,12 +522,11 @@ func (srv *Server) serveTCP(l net.Listener) error {
 			}
 			return err
 		}
-		go srv.serveTCPConn(handler, rw)
+		srv.spawnWorker(&response{tsigSecret: srv.TsigSecret, tcp: rw})
 	}
 }
 
 // serveUDP starts a UDP listener for the server.
-// Each request is handled in a separate goroutine.
 func (srv *Server) serveUDP(l *net.UDPConn) error {
 	defer l.Close()
 
@@ -483,10 +539,6 @@ func (srv *Server) serveUDP(l *net.UDPConn) error {
 		reader = srv.DecorateReader(reader)
 	}
 
-	handler := srv.Handler
-	if handler == nil {
-		handler = DefaultServeMux
-	}
 	rtimeout := srv.getReadTimeout()
 	// deadline is not used here
 	for {
@@ -506,24 +558,28 @@ func (srv *Server) serveUDP(l *net.UDPConn) error {
 		if len(m) < headerSize {
 			continue
 		}
-		go srv.serveUDPPacket(handler, m, l, s)
+		srv.spawnWorker(&response{msg: m, tsigSecret: srv.TsigSecret, udp: l, udpSession: s})
 	}
 }
 
-// Serve a new TCP connection.
-func (srv *Server) serveTCPConn(h Handler, t net.Conn) {
-	reader := Reader(&defaultReader{srv})
-	if srv.DecorateReader != nil {
-		reader = srv.DecorateReader(reader)
-	}
-
-	w := &response{tsigSecret: srv.TsigSecret, tcp: t}
+func (srv *Server) serve(w *response) {
 	if srv.DecorateWriter != nil {
 		w.writer = srv.DecorateWriter(w)
 	} else {
 		w.writer = w
 	}
 
+	if w.udp != nil {
+		// serve UDP
+		srv.serveDNS(w)
+		return
+	}
+
+	reader := Reader(&defaultReader{srv})
+	if srv.DecorateReader != nil {
+		reader = srv.DecorateReader(reader)
+	}
+
 	defer func() {
 		if !w.hijacked {
 			w.Close()
@@ -539,12 +595,13 @@ func (srv *Server) serveTCPConn(h Handler, t net.Conn) {
 
 	// TODO(miek): make maxTCPQueries configurable?
 	for q := 0; q < maxTCPQueries; q++ {
-		m, err := reader.ReadTCP(t, timeout)
+		var err error
+		w.msg, err = reader.ReadTCP(w.tcp, timeout)
 		if err != nil {
 			// TODO(tmthrgd): handle error
 			break
 		}
-		srv.serveDNS(h, m, w)
+		srv.serveDNS(w)
 		if w.tcp == nil {
 			break // Close() was called
 		}
@@ -557,20 +614,9 @@ func (srv *Server) serveTCPConn(h Handler, t net.Conn) {
 	}
 }
 
-// Serve a new UDP request.
-func (srv *Server) serveUDPPacket(h Handler, m []byte, u *net.UDPConn, s *SessionUDP) {
-	w := &response{tsigSecret: srv.TsigSecret, udp: u, udpSession: s}
-	if srv.DecorateWriter != nil {
-		w.writer = srv.DecorateWriter(w)
-	} else {
-		w.writer = w
-	}
-	srv.serveDNS(h, m, w)
-}
-
-func (srv *Server) serveDNS(h Handler, m []byte, w *response) {
+func (srv *Server) serveDNS(w *response) {
 	req := new(Msg)
-	err := req.Unpack(m)
+	err := req.Unpack(w.msg)
 	if err != nil { // Send a FormatError back
 		x := new(Msg)
 		x.SetRcodeFormatError(req)
@@ -585,7 +631,7 @@ func (srv *Server) serveDNS(h Handler, m []byte, w *response) {
 	if w.tsigSecret != nil {
 		if t := req.IsTsig(); t != nil {
 			if secret, ok := w.tsigSecret[t.Hdr.Name]; ok {
-				w.tsigStatus = TsigVerify(m, secret, "", false)
+				w.tsigStatus = TsigVerify(w.msg, secret, "", false)
 			} else {
 				w.tsigStatus = ErrSecret
 			}
@@ -593,7 +639,13 @@ func (srv *Server) serveDNS(h Handler, m []byte, w *response) {
 			w.tsigRequestMAC = req.Extra[len(req.Extra)-1].(*TSIG).MAC
 		}
 	}
-	h.ServeDNS(w, req) // Writes back to the client
+
+	handler := srv.Handler
+	if handler == nil {
+		handler = DefaultServeMux
+	}
+
+	handler.ServeDNS(w, req) // Writes back to the client
 }
 
 func (srv *Server) readTCP(conn net.Conn, timeout time.Duration) ([]byte, error) {