expvar: convert f to atomic type

For #53821

Change-Id: I2e7c5376e6ca3e3dbb2f92ad771aed62fca8b793
GitHub-Last-Rev: b67ddf81ec
GitHub-Pull-Request: golang/go#54864
Reviewed-on: https://go-review.googlesource.com/c/go/+/428195
Reviewed-by: Ian Lance Taylor <iant@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>
Auto-Submit: Ian Lance Taylor <iant@google.com>
Reviewed-by: Keith Randall <khr@google.com>
Run-TryBot: Ian Lance Taylor <iant@google.com>

src/expvar/expvar.go

@@ -67,26 +67,26 @@ func (v *Int) Set(value int64) {
 
 // Float is a 64-bit float variable that satisfies the Var interface.
 type Float struct {
-	f uint64
+	f atomic.Uint64
 }
 
 func (v *Float) Value() float64 {
-	return math.Float64frombits(atomic.LoadUint64(&v.f))
+	return math.Float64frombits(v.f.Load())
 }
 
 func (v *Float) String() string {
 	return strconv.FormatFloat(
-		math.Float64frombits(atomic.LoadUint64(&v.f)), 'g', -1, 64)
+		math.Float64frombits(v.f.Load()), 'g', -1, 64)
 }
 
 // Add adds delta to v.
 func (v *Float) Add(delta float64) {
 	for {
-		cur := atomic.LoadUint64(&v.f)
+		cur := v.f.Load()
 		curVal := math.Float64frombits(cur)
 		nxtVal := curVal + delta
 		nxt := math.Float64bits(nxtVal)
-		if atomic.CompareAndSwapUint64(&v.f, cur, nxt) {
+		if v.f.CompareAndSwap(cur, nxt) {
 			return
 		}
 	}
@@ -94,7 +94,7 @@ func (v *Float) Add(delta float64) {
 
 // Set sets v to value.
 func (v *Float) Set(value float64) {
-	atomic.StoreUint64(&v.f, math.Float64bits(value))
+	v.f.Store(math.Float64bits(value))
 }
 
 // Map is a string-to-Var map variable that satisfies the Var interface.

src/expvar/expvar_test.go

@@ -87,8 +87,8 @@ func BenchmarkIntSet(b *testing.B) {
 func TestFloat(t *testing.T) {
 	RemoveAll()
 	reqs := NewFloat("requests-float")
-	if reqs.f != 0.0 {
-		t.Errorf("reqs.f = %v, want 0", reqs.f)
+	if reqs.f.Load() != 0.0 {
+		t.Errorf("reqs.f = %v, want 0", reqs.f.Load())
 	}
 	if reqs != Get("requests-float").(*Float) {
 		t.Errorf("Get() failed.")