Use a lock instead of a goroutine for EWMA.

In this instance, it's way faster.

ewma.go

@@ -2,6 +2,7 @@ package metrics
 
 import (
 	"math"
+	"sync"
 	"sync/atomic"
 )
 
@@ -21,9 +22,10 @@ type EWMA interface {
 // to manage uncounted events.
 type StandardEWMA struct {
 	alpha     float64
+	init bool
+	mutex *sync.Mutex
+	rate float64
 	uncounted int64
-	in        chan bool
-	out       chan float64
 }
 
 // Force the compiler to check that StandardEWMA implements EWMA.
@@ -32,9 +34,10 @@ var _ EWMA = &StandardEWMA{}
 // Create a new EWMA with the given alpha.  Create the clock channel and
 // start the ticker goroutine.
 func NewEWMA(alpha float64) *StandardEWMA {
-	a := &StandardEWMA{alpha, 0, make(chan bool), make(chan float64)}
-	go a.arbiter()
-	return a
+	return &StandardEWMA{
+		alpha: alpha,
+		mutex: &sync.Mutex{},
+	}
 }
 
 // Create a new EWMA with alpha set for a one-minute moving average.
@@ -54,37 +57,25 @@ func NewEWMA15() *StandardEWMA {
 
 // Return the moving average rate of events per second.
 func (a *StandardEWMA) Rate() float64 {
-	return <-a.out * float64(1e9)
+	return a.rate * float64(1e9)
 }
 
 // Tick the clock to update the moving average.
 func (a *StandardEWMA) Tick() {
-	a.in <- true
+	count := atomic.LoadInt64(&a.uncounted)
+	atomic.AddInt64(&a.uncounted, -count)
+	instantRate := float64(count) / float64(5e9)
+	a.mutex.Lock()
+	defer a.mutex.Unlock()
+	if a.init {
+		a.rate += a.alpha * (instantRate - a.rate)
+	} else {
+		a.init = true
+		a.rate = instantRate
+	}
 }
 
 // Add n uncounted events.
 func (a *StandardEWMA) Update(n int64) {
 	atomic.AddInt64(&a.uncounted, n)
 }
-
-// On each clock tick, update the moving average to reflect the number of
-// events seen since the last tick.
-func (a *StandardEWMA) arbiter() {
-	var initialized bool
-	var rate float64
-	for {
-		select {
-		case <-a.in:
-			count := atomic.LoadInt64(&a.uncounted)
-			atomic.AddInt64(&a.uncounted, -count)
-			instantRate := float64(count) / float64(5e9)
-			if initialized {
-				rate += a.alpha * (instantRate - rate)
-			} else {
-				initialized = true
-				rate = instantRate
-			}
-		case a.out <- rate:
-		}
-	}
-}