BasicProgresssBar: protect add with a lock

to avoid weird race conditions.

packer/progressbar.go

@@ -31,8 +31,8 @@ type ProgressBar interface {
 // StackableProgressBar will clean itself to a default
 // state.
 type StackableProgressBar struct {
-	mtx sync.Mutex // locks in Start & Finish
-	BasicProgressBar
+	mtx   sync.Mutex // locks in Start, Finish, Add & NewProxyReader
+	Bar   BasicProgressBar
 	items int32
 	total int64
 
@@ -42,10 +42,10 @@ type StackableProgressBar struct {
 var _ ProgressBar = new(StackableProgressBar)
 
 func (spb *StackableProgressBar) start() {
-	spb.BasicProgressBar.ProgressBar = pb.New(0)
-	spb.BasicProgressBar.ProgressBar.SetUnits(pb.U_BYTES)
+	spb.Bar.ProgressBar = pb.New(0)
+	spb.Bar.ProgressBar.SetUnits(pb.U_BYTES)
 
-	spb.BasicProgressBar.ProgressBar.Start()
+	spb.Bar.ProgressBar.Start()
 	spb.started = true
 }
 
@@ -58,13 +58,25 @@ func (spb *StackableProgressBar) Start(total int64) {
 	if !spb.started {
 		spb.start()
 	}
-	spb.SetTotal64(spb.total)
+	spb.Bar.SetTotal64(spb.total)
 	spb.prefix()
 	spb.mtx.Unlock()
 }
 
+func (spb *StackableProgressBar) Add(total int64) {
+	spb.mtx.Lock()
+	defer spb.mtx.Unlock()
+	spb.Bar.Add(total)
+}
+
+func (spb *StackableProgressBar) NewProxyReader(r io.Reader) io.Reader {
+	spb.mtx.Lock()
+	defer spb.mtx.Unlock()
+	return spb.Bar.NewProxyReader(r)
+}
+
 func (spb *StackableProgressBar) prefix() {
-	spb.BasicProgressBar.ProgressBar.Prefix(fmt.Sprintf("%d items: ", atomic.LoadInt32(&spb.items)))
+	spb.Bar.ProgressBar.Prefix(fmt.Sprintf("%d items: ", atomic.LoadInt32(&spb.items)))
 }
 
 func (spb *StackableProgressBar) Finish() {
@@ -74,8 +86,8 @@ func (spb *StackableProgressBar) Finish() {
 	spb.items--
 	if spb.items == 0 {
 		// slef cleanup
-		spb.BasicProgressBar.ProgressBar.Finish()
-		spb.BasicProgressBar.ProgressBar = nil
+		spb.Bar.ProgressBar.Finish()
+		spb.Bar.ProgressBar = nil
 		spb.started = false
 		spb.total = 0
 		return