start collecting RTT and bandwidth metrics when Collect is calleed

metrics.go

@@ -54,8 +54,9 @@ func init() {
 }
 
 type aggregatingCollector struct {
-	mutex sync.Mutex
+	cronOnce sync.Once
 
+	mutex                sync.Mutex
 	highestID            uint64
 	conns                map[uint64] /* id */ *tracingConn
 	rtts                 prometheus.Histogram
@@ -80,7 +81,6 @@ func newAggregatingCollector() *aggregatingCollector {
 			Buckets: prometheus.ExponentialBuckets(1, 1.5, 40), // 1s to ~12 weeks
 		}),
 	}
-	go c.cron()
 	return c
 }
 
@@ -114,36 +114,47 @@ func (c *aggregatingCollector) cron() {
 	defer ticker.Stop()
 
 	for now := range ticker.C {
-		c.mutex.Lock()
-		c.segsSent = 0
-		c.segsRcvd = 0
-		c.bytesSent = 0
-		c.bytesRcvd = 0
-		for _, conn := range c.conns {
-			info, err := conn.getTCPInfo()
-			if err != nil {
-				if strings.Contains(err.Error(), "use of closed network connection") {
-					continue
-				}
-				log.Errorf("Failed to get TCP info: %s", err)
+		c.collectMetrics(now)
+	}
+}
+
+func (c *aggregatingCollector) collectMetrics(now time.Time) {
+	c.mutex.Lock()
+	defer c.mutex.Unlock()
+
+	c.segsSent = 0
+	c.segsRcvd = 0
+	c.bytesSent = 0
+	c.bytesRcvd = 0
+	for _, conn := range c.conns {
+		info, err := conn.getTCPInfo()
+		if err != nil {
+			if strings.Contains(err.Error(), "use of closed network connection") {
 				continue
 			}
-			if hasSegmentCounter {
-				c.segsSent += getSegmentsSent(info)
-				c.segsRcvd += getSegmentsRcvd(info)
-			}
-			if hasByteCounter {
-				c.bytesSent += getBytesSent(info)
-				c.bytesRcvd += getBytesRcvd(info)
-			}
-			c.rtts.Observe(info.RTT.Seconds())
-			c.connDurations.Observe(now.Sub(conn.startTime).Seconds())
+			log.Errorf("Failed to get TCP info: %s", err)
+			continue
 		}
-		c.mutex.Unlock()
+		if hasSegmentCounter {
+			c.segsSent += getSegmentsSent(info)
+			c.segsRcvd += getSegmentsRcvd(info)
+		}
+		if hasByteCounter {
+			c.bytesSent += getBytesSent(info)
+			c.bytesRcvd += getBytesRcvd(info)
+		}
+		c.rtts.Observe(info.RTT.Seconds())
+		c.connDurations.Observe(now.Sub(conn.startTime).Seconds())
 	}
 }
 
 func (c *aggregatingCollector) Collect(metrics chan<- prometheus.Metric) {
+	// Start collecting the metrics collection the first time Collect is called.
+	c.cronOnce.Do(func() {
+		c.collectMetrics(time.Now())
+		go c.cron()
+	})
+
 	c.mutex.Lock()
 	defer c.mutex.Unlock()