device: remove starting waitgroups

In each case, the starting waitgroup did nothing but ensure
that the goroutine has launched.

Nothing downstream depends on the order in which goroutines launch,
and if the Go runtime scheduler is so broken that goroutines
don't get launched reasonably promptly, we have much deeper problems.

Given all that, simplify the code.

Passed a race-enabled stress test 25,000 times without failure.

Signed-off-by: Josh Bleecher Snyder <josh@tailscale.com>

device/device.go

@@ -27,7 +27,6 @@ type Device struct {
 	// synchronized resources (locks acquired in order)
 
 	state struct {
-		starting sync.WaitGroup
 		stopping sync.WaitGroup
 		sync.Mutex
 		changing AtomicBool
@@ -35,7 +34,6 @@ type Device struct {
 	}
 
 	net struct {
-		starting sync.WaitGroup
 		stopping sync.WaitGroup
 		sync.RWMutex
 		bind          conn.Bind // bind interface
@@ -297,23 +295,18 @@ func NewDevice(tunDevice tun.Device, logger *Logger) *Device {
 	// start workers
 
 	cpus := runtime.NumCPU()
-	device.state.starting.Wait()
 	device.state.stopping.Wait()
 	for i := 0; i < cpus; i += 1 {
-		device.state.starting.Add(3)
 		device.state.stopping.Add(3)
 		go device.RoutineEncryption()
 		go device.RoutineDecryption()
 		go device.RoutineHandshake()
 	}
 
-	device.state.starting.Add(2)
 	device.state.stopping.Add(2)
 	go device.RoutineReadFromTUN()
 	go device.RoutineTUNEventReader()
 
-	device.state.starting.Wait()
-
 	return device
 }
 
@@ -370,8 +363,6 @@ func (device *Device) Close() {
 		return
 	}
 
-	device.state.starting.Wait()
-
 	device.log.Info.Println("Device closing")
 	device.state.changing.Set(true)
 	device.state.Lock()
@@ -527,11 +518,9 @@ func (device *Device) BindUpdate() error {
 
 		// start receiving routines
 
-		device.net.starting.Add(2)
 		device.net.stopping.Add(2)
 		go device.RoutineReceiveIncoming(ipv4.Version, netc.bind)
 		go device.RoutineReceiveIncoming(ipv6.Version, netc.bind)
-		device.net.starting.Wait()
 
 		device.log.Debug.Println("UDP bind has been updated")
 	}

device/peer.go

@@ -66,8 +66,7 @@ type Peer struct {
 	}
 
 	routines struct {
-		sync.Mutex                // held when stopping / starting routines
-		starting   sync.WaitGroup // routines pending start
+		sync.Mutex                // held when stopping routines
 		stopping   sync.WaitGroup // routines pending stop
 		stop       chan struct{}  // size 0, stop all go routines in peer
 	}
@@ -189,10 +188,8 @@ func (peer *Peer) Start() {
 
 	// reset routine state
 
-	peer.routines.starting.Wait()
 	peer.routines.stopping.Wait()
 	peer.routines.stop = make(chan struct{})
-	peer.routines.starting.Add(PeerRoutineNumber)
 	peer.routines.stopping.Add(PeerRoutineNumber)
 
 	// prepare queues
@@ -213,7 +210,6 @@ func (peer *Peer) Start() {
 	go peer.RoutineSequentialSender()
 	go peer.RoutineSequentialReceiver()
 
-	peer.routines.starting.Wait()
 	peer.isRunning.Set(true)
 }
 
@@ -270,8 +266,6 @@ func (peer *Peer) Stop() {
 		return
 	}
 
-	peer.routines.starting.Wait()
-
 	peer.routines.Lock()
 	defer peer.routines.Unlock()
 

device/receive.go

@@ -111,7 +111,6 @@ func (device *Device) RoutineReceiveIncoming(IP int, bind conn.Bind) {
 	}()
 
 	logDebug.Println("Routine: receive incoming IPv" + strconv.Itoa(IP) + " - started")
-	device.net.starting.Done()
 
 	// receive datagrams until conn is closed
 
@@ -246,7 +245,6 @@ func (device *Device) RoutineDecryption() {
 		device.state.stopping.Done()
 	}()
 	logDebug.Println("Routine: decryption worker - started")
-	device.state.starting.Done()
 
 	for {
 		select {
@@ -321,7 +319,6 @@ func (device *Device) RoutineHandshake() {
 	}()
 
 	logDebug.Println("Routine: handshake worker - started")
-	device.state.starting.Done()
 
 	for {
 		if elem.buffer != nil {
@@ -521,8 +518,6 @@ func (peer *Peer) RoutineSequentialReceiver() {
 
 	logDebug.Println(peer, "- Routine: sequential receiver - started")
 
-	peer.routines.starting.Done()
-
 	for {
 		if elem != nil {
 			if !elem.IsDropped() {

device/send.go

@@ -262,7 +262,6 @@ func (device *Device) RoutineReadFromTUN() {
 	}()
 
 	logDebug.Println("Routine: TUN reader - started")
-	device.state.starting.Done()
 
 	var elem *QueueOutboundElement
 
@@ -372,7 +371,6 @@ func (peer *Peer) RoutineNonce() {
 		peer.routines.stopping.Done()
 	}()
 
-	peer.routines.starting.Done()
 	logDebug.Println(peer, "- Routine: nonce worker - started")
 
 NextPacket:
@@ -507,7 +505,6 @@ func (device *Device) RoutineEncryption() {
 	}()
 
 	logDebug.Println("Routine: encryption worker - started")
-	device.state.starting.Done()
 
 	for {
 
@@ -596,8 +593,6 @@ func (peer *Peer) RoutineSequentialSender() {
 
 	logDebug.Println(peer, "- Routine: sequential sender - started")
 
-	peer.routines.starting.Done()
-
 	for {
 		select {
 

device/tun.go

@@ -20,7 +20,6 @@ func (device *Device) RoutineTUNEventReader() {
 	logError := device.log.Error
 
 	logDebug.Println("Routine: event worker - started")
-	device.state.starting.Done()
 
 	for event := range device.tun.device.Events() {
 		if event&tun.EventMTUUpdate != 0 {