Prevent Meter from being added twice

meter.go

@@ -32,6 +32,7 @@ func (s Snapshot) String() string {
 // Meter is a meter for monitoring a flow.
 type Meter struct {
 	accumulator uint64
+	registered  int32 // atomic bool
 
 	// Take lock.
 	snapshot Snapshot
@@ -39,10 +40,15 @@ type Meter struct {
 
 // Mark updates the total.
 func (m *Meter) Mark(count uint64) {
-	if count > 0 && atomic.AddUint64(&m.accumulator, count) == count {
-		// I'm the first one to bump this above 0.
-		// Register it.
-		globalSweeper.Register(m)
+	if count > 0 {
+		if atomic.AddUint64(&m.accumulator, count) == count {
+			just_registered := atomic.CompareAndSwapInt32(&m.registered, 0, 1)
+			if just_registered {
+				// I'm the first one to bump this above 0.
+				// Register it.
+				globalSweeper.Register(m)
+			}
+		}
 	}
 }
 

sweeper.go

@@ -113,6 +113,7 @@ func (sw *sweeper) update() {
 
 		// Mark this as idle by zeroing the accumulator.
 		swappedTotal := atomic.SwapUint64(&m.accumulator, 0)
+		atomic.StoreInt32(&m.registered, 0)
 
 		// So..., are we really idle?
 		if swappedTotal > total {