Limit GetMetricStatistics to 10 per second

closes #1197

internal/limiter/limiter.go

@@ -0,0 +1,59 @@
+package limiter
+
+import (
+	"sync"
+	"time"
+)
+
+// NewRateLimiter returns a rate limiter that will will emit from the C
+// channel only 'n' times every 'rate' seconds.
+func NewRateLimiter(n int, rate time.Duration) *rateLimiter {
+	r := &rateLimiter{
+		C:        make(chan bool),
+		rate:     rate,
+		n:        n,
+		shutdown: make(chan bool),
+	}
+	r.wg.Add(1)
+	go r.limiter()
+	return r
+}
+
+type rateLimiter struct {
+	C    chan bool
+	rate time.Duration
+	n    int
+
+	shutdown chan bool
+	wg       sync.WaitGroup
+}
+
+func (r *rateLimiter) Stop() {
+	close(r.shutdown)
+	r.wg.Wait()
+	close(r.C)
+}
+
+func (r *rateLimiter) limiter() {
+	defer r.wg.Done()
+	ticker := time.NewTicker(r.rate)
+	defer ticker.Stop()
+	counter := 0
+	for {
+		select {
+		case <-r.shutdown:
+			return
+		case <-ticker.C:
+			counter = 0
+		default:
+			if counter < r.n {
+				select {
+				case r.C <- true:
+					counter++
+				case <-r.shutdown:
+					return
+				}
+			}
+		}
+	}
+}

internal/limiter/limiter_test.go

@@ -0,0 +1,54 @@
+package limiter
+
+import (
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestRateLimiter(t *testing.T) {
+	r := NewRateLimiter(5, time.Second)
+	ticker := time.NewTicker(time.Millisecond * 75)
+
+	// test that we can only get 5 receives from the rate limiter
+	counter := 0
+outer:
+	for {
+		select {
+		case <-r.C:
+			counter++
+		case <-ticker.C:
+			break outer
+		}
+	}
+
+	assert.Equal(t, 5, counter)
+	r.Stop()
+	// verify that the Stop function closes the channel.
+	_, ok := <-r.C
+	assert.False(t, ok)
+}
+
+func TestRateLimiterMultipleIterations(t *testing.T) {
+	r := NewRateLimiter(5, time.Millisecond*50)
+	ticker := time.NewTicker(time.Millisecond * 250)
+
+	// test that we can get 15 receives from the rate limiter
+	counter := 0
+outer:
+	for {
+		select {
+		case <-ticker.C:
+			break outer
+		case <-r.C:
+			counter++
+		}
+	}
+
+	assert.True(t, counter > 10)
+	r.Stop()
+	// verify that the Stop function closes the channel.
+	_, ok := <-r.C
+	assert.False(t, ok)
+}