Set time unit on metrics.Timer

metrics/timer.go

@@ -7,22 +7,30 @@ import "time"
 type Timer struct {
 	h Histogram
 	t time.Time
+	u time.Duration
 }
 
 // NewTimer wraps the given histogram and records the current time.
 func NewTimer(h Histogram) *Timer {
 	return &Timer{
 		h: h,
 		t: time.Now(),
+		u: time.Second,
 	}
 }
 
 // ObserveDuration captures the number of seconds since the timer was
 // constructed, and forwards that observation to the histogram.
 func (t *Timer) ObserveDuration() {
-	d := time.Since(t.t).Seconds()
+	d := float64(time.Since(t.t).Nanoseconds()) / float64(t.u)
 	if d < 0 {
 		d = 0
 	}
 	t.h.Observe(d)
 }
+
+// Unit sets the unit of the float64 emitted by the timer.
+// By default, the timer emits seconds.
+func (t *Timer) Unit(u time.Duration) {
+	t.u = u
+}

metrics/timer_test.go

@@ -31,3 +31,28 @@ func TestTimerSlow(t *testing.T) {
 		t.Errorf("want %.3f, have %.3f", want, have)
 	}
 }
+
+func TestTimerUnit(t *testing.T) {
+	for _, tc := range []struct {
+		name      string
+		unit      time.Duration
+		tolerance float64
+		want      float64
+	}{
+		{"Seconds", time.Second, 0.010, 0.100},
+		{"Milliseconds", time.Millisecond, 10, 100},
+		{"Nanoseconds", time.Nanosecond, 10000000, 100000000},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			h := generic.NewSimpleHistogram()
+			timer := metrics.NewTimer(h)
+			time.Sleep(100 * time.Millisecond)
+			timer.Unit(tc.unit)
+			timer.ObserveDuration()
+
+			if want, have := tc.want, h.ApproximateMovingAverage(); math.Abs(want-have) > tc.tolerance {
+				t.Errorf("want %.3f, have %.3f", want, have)
+			}
+		})
+	}
+}