From 284bad20d83ddb85337dd15d91307de3004980a0 Mon Sep 17 00:00:00 2001
From: Miek Gieben <miek@miek.nl>
Date: Sat, 9 Mar 2019 13:34:22 +0000
Subject: [PATCH] Manually revert go workers (98a1ef45) (#928)

Manually revert the worker model.

Signed-off-by: Miek Gieben <miek@miek.nl>
---
 server.go | 110 +++++++-----------------------------------------------
 1 file changed, 14 insertions(+), 96 deletions(-)

diff --git a/server.go b/server.go
index d4364d6e..0917e0cf 100644
--- a/server.go
+++ b/server.go
@@ -12,26 +12,12 @@ import (
 	"net"
 	"strings"
 	"sync"
-	"sync/atomic"
 	"time"
 )
 
 // Default maximum number of TCP queries before we close the socket.
 const maxTCPQueries = 128
 
-// The maximum number of idle workers.
-//
-// This controls the maximum number of workers that are allowed to stay
-// idle waiting for incoming requests before being torn down.
-//
-// If this limit is reached, the server will just keep spawning new
-// workers (goroutines) for each incoming request. In this case, each
-// worker will only be used for a single request.
-const maxIdleWorkersCount = 10000
-
-// The maximum length of time a worker may idle for before being destroyed.
-const idleWorkerTimeout = 10 * time.Second
-
 // aLongTimeAgo is a non-zero time, far in the past, used for
 // immediate cancelation of network operations.
 var aLongTimeAgo = time.Unix(1, 0)
@@ -92,7 +78,6 @@ type response struct {
 	tcp            net.Conn          // i/o connection if TCP was used
 	udpSession     *SessionUDP       // oob data to get egress interface right
 	writer         Writer            // writer to output the raw DNS bits
-	wg             *sync.WaitGroup   // for gracefull shutdown
 }
 
 // HandleFailed returns a HandlerFunc that returns SERVFAIL for every request it gets.
@@ -218,11 +203,6 @@ type Server struct {
 	// By default DefaultMsgAcceptFunc will be used.
 	MsgAcceptFunc MsgAcceptFunc
 
-	// UDP packet or TCP connection queue
-	queue chan *response
-	// Workers count
-	workersCount int32
-
 	// Shutdown handling
 	lock     sync.RWMutex
 	started  bool
@@ -240,51 +220,6 @@ func (srv *Server) isStarted() bool {
 	return started
 }
 
-func (srv *Server) worker(w *response) {
-	srv.serve(w)
-
-	for {
-		count := atomic.LoadInt32(&srv.workersCount)
-		if count > maxIdleWorkersCount {
-			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)
-	}
-}
-
 func makeUDPBuffer(size int) func() interface{} {
 	return func() interface{} {
 		return make([]byte, size)
@@ -292,8 +227,6 @@ func makeUDPBuffer(size int) func() interface{} {
 }
 
 func (srv *Server) init() {
-	srv.queue = make(chan *response)
-
 	srv.shutdown = make(chan struct{})
 	srv.conns = make(map[net.Conn]struct{})
 
@@ -328,7 +261,6 @@ func (srv *Server) ListenAndServe() error {
 	}
 
 	srv.init()
-	defer close(srv.queue)
 
 	switch srv.Net {
 	case "tcp", "tcp4", "tcp6":
@@ -383,7 +315,6 @@ func (srv *Server) ActivateAndServe() error {
 	}
 
 	srv.init()
-	defer close(srv.queue)
 
 	pConn := srv.PacketConn
 	l := srv.Listener
@@ -499,11 +430,7 @@ func (srv *Server) serveTCP(l net.Listener) error {
 		srv.conns[rw] = struct{}{}
 		srv.lock.Unlock()
 		wg.Add(1)
-		srv.spawnWorker(&response{
-			tsigSecret: srv.TsigSecret,
-			tcp:        rw,
-			wg:         &wg,
-		})
+		go srv.serve(&response{tsigSecret: srv.TsigSecret, tcp: rw}, &wg)
 	}
 
 	return nil
@@ -548,19 +475,13 @@ func (srv *Server) serveUDP(l *net.UDPConn) error {
 			continue
 		}
 		wg.Add(1)
-		srv.spawnWorker(&response{
-			msg:        m,
-			tsigSecret: srv.TsigSecret,
-			udp:        l,
-			udpSession: s,
-			wg:         &wg,
-		})
+		go srv.serve(&response{msg: m, tsigSecret: srv.TsigSecret, udp: l, udpSession: s}, &wg)
 	}
 
 	return nil
 }
 
-func (srv *Server) serve(w *response) {
+func (srv *Server) serve(w *response, wg *sync.WaitGroup) {
 	if srv.DecorateWriter != nil {
 		w.writer = srv.DecorateWriter(w)
 	} else {
@@ -570,23 +491,10 @@ func (srv *Server) serve(w *response) {
 	if w.udp != nil {
 		// serve UDP
 		srv.serveDNS(w)
-
-		w.wg.Done()
+		wg.Done()
 		return
 	}
 
-	defer func() {
-		if !w.hijacked {
-			w.Close()
-		}
-
-		srv.lock.Lock()
-		delete(srv.conns, w.tcp)
-		srv.lock.Unlock()
-
-		w.wg.Done()
-	}()
-
 	reader := Reader(defaultReader{srv})
 	if srv.DecorateReader != nil {
 		reader = srv.DecorateReader(reader)
@@ -622,6 +530,16 @@ func (srv *Server) serve(w *response) {
 		// idle timeout.
 		timeout = idleTimeout
 	}
+
+	if !w.hijacked {
+		w.Close()
+	}
+
+	srv.lock.Lock()
+	delete(srv.conns, w.tcp)
+	srv.lock.Unlock()
+
+	wg.Done()
 }
 
 func (srv *Server) disposeBuffer(w *response) {