Revert "metrics: use atomic type (#27121)"

This reverts commit 9f88fe2b74.

metrics/counter.go

@@ -38,13 +38,13 @@ func NewCounter() Counter {
 	if !Enabled {
 		return NilCounter{}
 	}
-	return &StandardCounter{}
+	return &StandardCounter{0}
 }
 
 // NewCounterForced constructs a new StandardCounter and returns it no matter if
 // the global switch is enabled or not.
 func NewCounterForced() Counter {
-	return &StandardCounter{}
+	return &StandardCounter{0}
 }
 
 // NewRegisteredCounter constructs and registers a new StandardCounter.
@@ -115,27 +115,27 @@ func (NilCounter) Snapshot() Counter { return NilCounter{} }
 // StandardCounter is the standard implementation of a Counter and uses the
 // sync/atomic package to manage a single int64 value.
 type StandardCounter struct {
-	count atomic.Int64
+	count int64
 }
 
 // Clear sets the counter to zero.
 func (c *StandardCounter) Clear() {
-	c.count.Store(0)
+	atomic.StoreInt64(&c.count, 0)
 }
 
 // Count returns the current count.
 func (c *StandardCounter) Count() int64 {
-	return c.count.Load()
+	return atomic.LoadInt64(&c.count)
 }
 
 // Dec decrements the counter by the given amount.
 func (c *StandardCounter) Dec(i int64) {
-	c.count.Add(-i)
+	atomic.AddInt64(&c.count, -i)
 }
 
 // Inc increments the counter by the given amount.
 func (c *StandardCounter) Inc(i int64) {
-	c.count.Add(i)
+	atomic.AddInt64(&c.count, i)
 }
 
 // Snapshot returns a read-only copy of the counter.

metrics/ewma.go

@@ -75,7 +75,7 @@ func (NilEWMA) Update(n int64) {}
 // of uncounted events and processes them on each tick.  It uses the
 // sync/atomic package to manage uncounted events.
 type StandardEWMA struct {
-	uncounted atomic.Int64
+	uncounted int64 // /!\ this should be the first member to ensure 64-bit alignment
 	alpha     float64
 	rate      float64
 	init      bool
@@ -97,8 +97,8 @@ func (a *StandardEWMA) Snapshot() EWMA {
 // Tick ticks the clock to update the moving average.  It assumes it is called
 // every five seconds.
 func (a *StandardEWMA) Tick() {
-	count := a.uncounted.Load()
+	count := atomic.LoadInt64(&a.uncounted)
-	a.uncounted.Add(-count)
+	atomic.AddInt64(&a.uncounted, -count)
 	instantRate := float64(count) / float64(5*time.Second)
 	a.mutex.Lock()
 	defer a.mutex.Unlock()
@@ -112,5 +112,5 @@ func (a *StandardEWMA) Tick() {
 
 // Update adds n uncounted events.
 func (a *StandardEWMA) Update(n int64) {
-	a.uncounted.Add(n)
+	atomic.AddInt64(&a.uncounted, n)
 }

metrics/gauge.go

@@ -25,7 +25,7 @@ func NewGauge() Gauge {
 	if !Enabled {
 		return NilGauge{}
 	}
-	return &StandardGauge{}
+	return &StandardGauge{0}
 }
 
 // NewRegisteredGauge constructs and registers a new StandardGauge.
@@ -101,7 +101,7 @@ func (NilGauge) Value() int64 { return 0 }
 // StandardGauge is the standard implementation of a Gauge and uses the
 // sync/atomic package to manage a single int64 value.
 type StandardGauge struct {
-	value atomic.Int64
+	value int64
 }
 
 // Snapshot returns a read-only copy of the gauge.
@@ -111,22 +111,22 @@ func (g *StandardGauge) Snapshot() Gauge {
 
 // Update updates the gauge's value.
 func (g *StandardGauge) Update(v int64) {
-	g.value.Store(v)
+	atomic.StoreInt64(&g.value, v)
 }
 
 // Value returns the gauge's current value.
 func (g *StandardGauge) Value() int64 {
-	return g.value.Load()
+	return atomic.LoadInt64(&g.value)
 }
 
 // Dec decrements the gauge's current value by the given amount.
 func (g *StandardGauge) Dec(i int64) {
-	g.value.Add(-i)
+	atomic.AddInt64(&g.value, -i)
 }
 
 // Inc increments the gauge's current value by the given amount.
 func (g *StandardGauge) Inc(i int64) {
-	g.value.Add(i)
+	atomic.AddInt64(&g.value, i)
 }
 
 // FunctionalGauge returns value from given function

metrics/meter.go

@@ -101,7 +101,11 @@ func NewRegisteredMeterForced(name string, r Registry) Meter {
 
 // MeterSnapshot is a read-only copy of another Meter.
 type MeterSnapshot struct {
-	temp                           atomic.Int64
+	// WARNING: The `temp` field is accessed atomically.
+	// On 32 bit platforms, only 64-bit aligned fields can be atomic. The struct is
+	// guaranteed to be so aligned, so take advantage of that. For more information,
+	// see https://golang.org/pkg/sync/atomic/#pkg-note-BUG.
+	temp                           int64
 	count                          int64
 	rate1, rate5, rate15, rateMean float64
 }
@@ -169,7 +173,7 @@ type StandardMeter struct {
 	snapshot    *MeterSnapshot
 	a1, a5, a15 EWMA
 	startTime   time.Time
-	stopped     atomic.Bool
+	stopped     uint32
 }
 
 func newStandardMeter() *StandardMeter {
@@ -184,8 +188,8 @@ func newStandardMeter() *StandardMeter {
 
 // Stop stops the meter, Mark() will be a no-op if you use it after being stopped.
 func (m *StandardMeter) Stop() {
-	stopped := m.stopped.Swap(true)
+	stopped := atomic.SwapUint32(&m.stopped, 1)
-	if !stopped {
+	if stopped != 1 {
 		arbiter.Lock()
 		delete(arbiter.meters, m)
 		arbiter.Unlock()
@@ -203,7 +207,7 @@ func (m *StandardMeter) Count() int64 {
 
 // Mark records the occurrence of n events.
 func (m *StandardMeter) Mark(n int64) {
-	m.snapshot.temp.Add(n)
+	atomic.AddInt64(&m.snapshot.temp, n)
 }
 
 // Rate1 returns the one-minute moving average rate of events per second.
@@ -237,14 +241,7 @@ func (m *StandardMeter) RateMean() float64 {
 // Snapshot returns a read-only copy of the meter.
 func (m *StandardMeter) Snapshot() Meter {
 	m.lock.RLock()
-	snapshot := MeterSnapshot{
+	snapshot := *m.snapshot
-		count:    m.snapshot.count,
-		rate1:    m.snapshot.rate1,
-		rate5:    m.snapshot.rate5,
-		rate15:   m.snapshot.rate15,
-		rateMean: m.snapshot.rateMean,
-	}
-	snapshot.temp.Store(m.snapshot.temp.Load())
 	m.lock.RUnlock()
 	return &snapshot
 }
@@ -260,7 +257,7 @@ func (m *StandardMeter) updateSnapshot() {
 
 func (m *StandardMeter) updateMeter() {
 	// should only run with write lock held on m.lock
-	n := m.snapshot.temp.Swap(0)
+	n := atomic.SwapInt64(&m.snapshot.temp, 0)
 	m.snapshot.count += n
 	m.a1.Update(n)
 	m.a5.Update(n)