device: call wg.Add outside the goroutine

One of the first rules of WaitGroups is that you call wg.Add
outside of a goroutine, not inside it. Fix this embarrassing mistake.

This prevents an extremely rare race condition (2 per 100,000 runs)
which could occur when attempting to start a new peer
concurrently with shutting down a device.

Signed-off-by: Josh Bleecher Snyder <[email protected]>

Author: josharian

device/peer.go

@@ -213,6 +213,8 @@ func (peer *Peer) Start() {
 
 	// wait for routines to start
 
+	// RoutineNonce writes to the encryption queue; keep it alive until we are done.
+	device.queue.encryption.wg.Add(1)
 	go peer.RoutineNonce()
 	go peer.RoutineSequentialSender()
 	go peer.RoutineSequentialReceiver()

device/send.go

@@ -352,9 +352,6 @@ func (peer *Peer) RoutineNonce() {
 	device := peer.device
 	logDebug := device.log.Debug
 
-	// We write to the encryption queue; keep it alive until we are done.
-	device.queue.encryption.wg.Add(1)
-
 	flush := func() {
 		for {
 			select {