From 7497a2027baf59ff1ee3655745f141fbc4f559ba Mon Sep 17 00:00:00 2001
From: Daniel Nelson <daniel@wavesofdawn.com>
Date: Wed, 26 Dec 2018 19:36:10 -0800
Subject: [PATCH] Deliver empty metric tracking group immediately (#5176)

---
 agent/accumulator_test.go | 16 +++++++++++++++-
 metric/tracking.go        | 28 ++++++++++++++++++----------
 2 files changed, 33 insertions(+), 11 deletions(-)

diff --git a/agent/accumulator_test.go b/agent/accumulator_test.go
index 2bb08920f..316ad124b 100644
--- a/agent/accumulator_test.go
+++ b/agent/accumulator_test.go
@@ -9,7 +9,6 @@ import (
 	"time"
 
 	"github.com/influxdata/telegraf"
-
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 )
@@ -127,6 +126,21 @@ func TestSetPrecision(t *testing.T) {
 	}
 }
 
+func TestAddTrackingMetricGroupEmpty(t *testing.T) {
+	ch := make(chan telegraf.Metric, 10)
+	metrics := []telegraf.Metric{}
+	acc := NewAccumulator(&TestMetricMaker{}, ch).WithTracking(1)
+
+	id := acc.AddTrackingMetricGroup(metrics)
+
+	select {
+	case tracking := <-acc.Delivered():
+		require.Equal(t, tracking.ID(), id)
+	default:
+		t.Fatal("empty group should be delivered immediately")
+	}
+}
+
 type TestMetricMaker struct {
 }
 
diff --git a/metric/tracking.go b/metric/tracking.go
index 83c3c7aec..3d8843240 100644
--- a/metric/tracking.go
+++ b/metric/tracking.go
@@ -50,7 +50,7 @@ type trackingData struct {
 	rc          int32
 	acceptCount int32
 	rejectCount int32
-	notify      NotifyFunc
+	notifyFunc  NotifyFunc
 }
 
 func (d *trackingData) incr() {
@@ -69,6 +69,16 @@ func (d *trackingData) reject() {
 	atomic.AddInt32(&d.rejectCount, 1)
 }
 
+func (d *trackingData) notify() {
+	d.notifyFunc(
+		&deliveryInfo{
+			id:       d.id,
+			accepted: int(d.acceptCount),
+			rejected: int(d.rejectCount),
+		},
+	)
+}
+
 type trackingMetric struct {
 	telegraf.Metric
 	d *trackingData
@@ -82,7 +92,7 @@ func newTrackingMetric(metric telegraf.Metric, fn NotifyFunc) (telegraf.Metric,
 			rc:          1,
 			acceptCount: 0,
 			rejectCount: 0,
-			notify:      fn,
+			notifyFunc:  fn,
 		},
 	}
 
@@ -98,7 +108,7 @@ func newTrackingMetricGroup(group []telegraf.Metric, fn NotifyFunc) ([]telegraf.
 		rc:          0,
 		acceptCount: 0,
 		rejectCount: 0,
-		notify:      fn,
+		notifyFunc:  fn,
 	}
 
 	for i, m := range group {
@@ -114,6 +124,10 @@ func newTrackingMetricGroup(group []telegraf.Metric, fn NotifyFunc) ([]telegraf.
 		runtime.SetFinalizer(d, finalizer)
 	}
 
+	if len(group) == 0 {
+		d.notify()
+	}
+
 	return group, d.id
 }
 
@@ -146,13 +160,7 @@ func (m *trackingMetric) decr() {
 	}
 
 	if v == 0 {
-		m.d.notify(
-			&deliveryInfo{
-				id:       m.d.id,
-				accepted: int(m.d.acceptCount),
-				rejected: int(m.d.rejectCount),
-			},
-		)
+		m.d.notify()
 	}
 }