chore: switch to typed atomics

This just means we can be less concerned about struct field ordering and
other details.

flow_test.go

@@ -3,7 +3,6 @@ package flow
 import (
 	"math"
 	"sync"
-	"sync/atomic"
 	"testing"
 	"time"
 )
@@ -106,7 +105,7 @@ func TestUnregister(t *testing.T) {
 
 	mockClock.Add(62 * time.Second)
 
-	if atomic.LoadUint64(&m.accumulator) != 0 {
+	if m.accumulator.Load() != 0 {
 		t.Error("expected meter to be paused")
 	}
 
@@ -131,7 +130,7 @@ func TestUnregister(t *testing.T) {
 	if actual.Total != 120 {
 		t.Errorf("expected total 120, got %d", actual.Total)
 	}
-	if atomic.LoadUint64(&m.accumulator) == 0 {
+	if m.accumulator.Load() == 0 {
 		t.Error("expected meter to be active")
 	}
 

meter.go

@@ -31,7 +31,7 @@ func (s Snapshot) String() string {
 
 // Meter is a meter for monitoring a flow.
 type Meter struct {
-	accumulator uint64
+	accumulator atomic.Uint64
 
 	// managed by the sweeper loop.
 	registered bool
@@ -42,7 +42,7 @@ type Meter struct {
 
 // Mark updates the total.
 func (m *Meter) Mark(count uint64) {
-	if count > 0 && atomic.AddUint64(&m.accumulator, count) == count {
+	if count > 0 && m.accumulator.Add(count) == count {
 		// The accumulator is 0 so we probably need to register. We may
 		// already _be_ registered however, if we are, the registration
 		// loop will notice that `m.registered` is set and ignore us.
@@ -60,7 +60,7 @@ func (m *Meter) Snapshot() Snapshot {
 // Reset sets accumulator, total and rate to zero.
 func (m *Meter) Reset() {
 	globalSweeper.snapshotMu.Lock()
-	atomic.StoreUint64(&m.accumulator, 0)
+	m.accumulator.Store(0)
 	m.snapshot.Rate = 0
 	m.snapshot.Total = 0
 	globalSweeper.snapshotMu.Unlock()

meter_test.go

@@ -3,6 +3,7 @@ package flow
 import (
 	"testing"
 	"time"
+	"unsafe"
 )
 
 func TestResetMeter(t *testing.T) {

sweeper.go

@@ -3,7 +3,6 @@ package flow
 import (
 	"math"
 	"sync"
-	"sync/atomic"
 	"time"
 
 	"github.com/benbjohnson/clock"
@@ -100,7 +99,7 @@ func (sw *sweeper) update() {
 
 	// Calculate the bandwidth for all active meters.
 	for i, m := range sw.meters[:sw.activeMeters] {
-		total := atomic.LoadUint64(&m.accumulator)
+		total := m.accumulator.Load()
 		diff := total - m.snapshot.Total
 		instant := timeMultiplier * float64(diff)
 
@@ -124,7 +123,7 @@ func (sw *sweeper) update() {
 		// Ok, so we are idle...
 
 		// Mark this as idle by zeroing the accumulator.
-		swappedTotal := atomic.SwapUint64(&m.accumulator, 0)
+		swappedTotal := m.accumulator.Swap(0)
 
 		// So..., are we really idle?
 		if swappedTotal > total {
@@ -134,7 +133,7 @@ func (sw *sweeper) update() {
 			// First, add back what we removed. If we can do this
 			// fast enough, we can put it back before anyone
 			// notices.
-			currentTotal := atomic.AddUint64(&m.accumulator, swappedTotal)
+			currentTotal := m.accumulator.Add(swappedTotal)
 
 			// Did we make it?
 			if currentTotal == swappedTotal {
@@ -150,7 +149,7 @@ func (sw *sweeper) update() {
 			// `^uint64(total - 1)` is the two's complement of
 			// `total`. It's the "correct" way to subtract
 			// atomically in go.
-			atomic.AddUint64(&m.accumulator, ^uint64(m.snapshot.Total-1))
+			m.accumulator.Add(^uint64(m.snapshot.Total - 1))
 		}
 
 		// Reset the rate, keep the total.
@@ -163,7 +162,7 @@ func (sw *sweeper) update() {
 	// 1. We don't do this on register to avoid having to take the snapshot lock.
 	// 2. We skip calculating the bandwidth for this round so we get an _accurate_ bandwidth calculation.
 	for _, m := range sw.meters[sw.activeMeters:] {
-		total := atomic.AddUint64(&m.accumulator, m.snapshot.Total)
+		total := m.accumulator.Add(m.snapshot.Total)
 		if total > m.snapshot.Total {
 			m.snapshot.LastUpdate = now
 		}