correctly set the initial total

The previous attempt actually make the problem worse:

1. It didn't update the "last update" time.
2. It updated the accumulator but then didn't set the total. That meant that the
_next_ update would count the bandwidth from two time periods.

This change also reverts the changes to the test (the test was right, the code
was wrong).

flow_test.go

@@ -108,9 +108,6 @@ func TestUnregister(t *testing.T) {
 		m := new(Meter)
 		go func() {
 			defer wg.Done()
-			m.Mark(1)
-			time.Sleep(time.Second)
-
 			ticker := time.NewTicker(100 * time.Millisecond)
 			defer ticker.Stop()
 			for i := 0; i < 40; i++ {
@@ -120,17 +117,14 @@ func TestUnregister(t *testing.T) {
 
 			time.Sleep(62 * time.Second)
 
-			m.Mark(2)
-			time.Sleep(time.Second)
-
 			for i := 0; i < 40; i++ {
 				m.Mark(2)
 				<-ticker.C
 			}
 		}()
 		go func() {
 			defer wg.Done()
-			time.Sleep(40*100*time.Millisecond + time.Second)
+			time.Sleep(40 * 100 * time.Millisecond)
 
 			actual := m.Snapshot()
 			if !approxEq(actual.Rate, 10, 1) {
@@ -143,19 +137,19 @@ func TestUnregister(t *testing.T) {
 			}
 
 			actual = m.Snapshot()
-			if actual.Total != 41 {
-				t.Errorf("expected total 41, got %d", actual.Total)
+			if actual.Total != 40 {
+				t.Errorf("expected total 4000, got %d", actual.Total)
 			}
-			time.Sleep(3*time.Second + 40*100*time.Millisecond)
+			time.Sleep(2*time.Second + 40*100*time.Millisecond)
 
 			actual = m.Snapshot()
 			if !approxEq(actual.Rate, 20, 4) {
 				t.Errorf("expected rate 20 (±4), got %f", actual.Rate)
 			}
 			time.Sleep(2 * time.Second)
 			actual = m.Snapshot()
-			if actual.Total != 123 {
-				t.Errorf("expected total 123, got %d", actual.Total)
+			if actual.Total != 120 {
+				t.Errorf("expected total 120, got %d", actual.Total)
 			}
 			if atomic.LoadUint64(&m.accumulator) == 0 {
 				t.Error("expected meter to be active")

registry_test.go

@@ -15,7 +15,7 @@ func TestRegistry(t *testing.T) {
 	m1.Mark(10)
 	m2.Mark(30)
 
-	time.Sleep(2 * time.Second)
+	time.Sleep(2*time.Second + time.Millisecond)
 
 	if total := r.Get("first").Snapshot().Total; total != 10 {
 		t.Errorf("expected first total to be 10, got %d", total)

sweeper.go

@@ -151,11 +151,15 @@ func (sw *sweeper) update() {
 		sw.meters[i] = sw.meters[newLen]
 	}
 
-	// Re-add the total to all the newly active accumulators.
+	// Re-add the total to all the newly active accumulators and set the snapshot to the total.
 	// 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:] {
-		atomic.AddUint64(&m.accumulator, m.snapshot.Total)
+		total := atomic.AddUint64(&m.accumulator, m.snapshot.Total)
+		if total > m.snapshot.Total {
+			m.snapshot.LastUpdate = now
+		}
+		m.snapshot.Total = total
 	}
 
 	// trim the meter list