Initialize counter created timestamp during metric initialization

Signed-off-by: Arthur Silva Sens <arthur.sens@coralogix.com>

prometheus/counter.go

@@ -93,6 +93,7 @@ func NewCounter(opts CounterOpts) Counter {
 	)
 	result := &counter{desc: desc, labelPairs: desc.constLabelPairs, now: time.Now}
 	result.init(result) // Init self-collection.
+	result.initCreated()
 	return result
 }
 
@@ -114,6 +115,10 @@ type counter struct {
 	now func() time.Time // To mock out time.Now() for testing.
 }
 
+func (c *counter) initCreated() {
+	c.createdTs = timestamppb.New(c.now())
+}
+
 func (c *counter) Desc() *Desc {
 	return c.desc
 }
@@ -123,10 +128,6 @@ func (c *counter) Add(v float64) {
 		panic(errors.New("counter cannot decrease in value"))
 	}
 
-	if c.createdTs == nil {
-		c.createdTs = timestamppb.New(c.now())
-	}
-
 	ival := uint64(v)
 	if float64(ival) == v {
 		atomic.AddUint64(&c.valInt, ival)
@@ -149,9 +150,6 @@ func (c *counter) AddWithExemplar(v float64, e Labels) {
 
 func (c *counter) Inc() {
 	atomic.AddUint64(&c.valInt, 1)
-	if c.createdTs == nil {
-		c.createdTs = timestamppb.New(c.now())
-	}
 }
 
 func (c *counter) get() float64 {

prometheus/counter_test.go

@@ -282,6 +282,32 @@ func TestCounterCreatedTimestamp(t *testing.T) {
 		Help: "test help",
 	}).(*counter)
 	counter.now = func() time.Time { return now }
+	counter.initCreated()
+
+	ts := timestamppb.New(now)
+	if err := ts.CheckValid(); err != nil {
+		t.Fatal(err)
+	}
+
+	expectedCounter := &dto.Counter{
+		CreatedTimestamp: ts,
+	}
+
+	if counter.createdTs.AsTime() != expectedCounter.CreatedTimestamp.AsTime() {
+		t.Errorf("expected created timestamp %s, got %s", expectedCounter.CreatedTimestamp, counter.createdTs)
+	}
+}
+
+func TestCounterVecCreatedTimestamp(t *testing.T) {
+	now := time.Now()
+
+	counterVec := NewCounterVec(CounterOpts{
+		Name: "test",
+		Help: "test help",
+	}, []string{"label"})
+	counter := counterVec.WithLabelValues("value").(*counter)
+	counter.now = func() time.Time { return now }
+	counter.initCreated()
 
 	ts := timestamppb.New(now)
 	if err := ts.CheckValid(); err != nil {
@@ -292,7 +318,6 @@ func TestCounterCreatedTimestamp(t *testing.T) {
 		CreatedTimestamp: ts,
 	}
 
-	counter.Inc()
 	if counter.createdTs.AsTime() != expectedCounter.CreatedTimestamp.AsTime() {
 		t.Errorf("expected created timestamp %s, got %s", expectedCounter.CreatedTimestamp, counter.createdTs)
 	}