expvar: add missing locking in String methods

R=golang-dev, rsc
CC=golang-dev
https://golang.org/cl/5726062

src/pkg/expvar/expvar.go

@@ -44,7 +44,11 @@ type Int struct {
 	mu sync.Mutex
 }
 
-func (v *Int) String() string { return strconv.FormatInt(v.i, 10) }
+func (v *Int) String() string {
+	v.mu.Lock()
+	defer v.mu.Unlock()
+	return strconv.FormatInt(v.i, 10)
+}
 
 func (v *Int) Add(delta int64) {
 	v.mu.Lock()
@@ -64,7 +68,11 @@ type Float struct {
 	mu sync.Mutex
 }
 
-func (v *Float) String() string { return strconv.FormatFloat(v.f, 'g', -1, 64) }
+func (v *Float) String() string {
+	v.mu.Lock()
+	defer v.mu.Unlock()
+	return strconv.FormatFloat(v.f, 'g', -1, 64)
+}
 
 // Add adds delta to v.
 func (v *Float) Add(delta float64) {
@@ -95,17 +103,17 @@ type KeyValue struct {
 func (v *Map) String() string {
 	v.mu.RLock()
 	defer v.mu.RUnlock()
-	b := new(bytes.Buffer)
-	fmt.Fprintf(b, "{")
+	var b bytes.Buffer
+	fmt.Fprintf(&b, "{")
 	first := true
 	for key, val := range v.m {
 		if !first {
-			fmt.Fprintf(b, ", ")
+			fmt.Fprintf(&b, ", ")
 		}
-		fmt.Fprintf(b, "\"%s\": %v", key, val)
+		fmt.Fprintf(&b, "\"%s\": %v", key, val)
 		first = false
 	}
-	fmt.Fprintf(b, "}")
+	fmt.Fprintf(&b, "}")
 	return b.String()
 }