pkg/services: add Ticker

pkg/services/ticker.go

@@ -0,0 +1,40 @@
+package services
+
+import (
+	"time"
+
+	"github.com/smartcontractkit/chainlink-common/pkg/utils"
+)
+
+// Ticker is like time.Ticker, but with two differences:
+// - the first tick is fired immediately
+// - each period has jitter applied by utils.WithJitter.
+type Ticker struct {
+	C    <-chan time.Time
+	stop StopChan
+}
+
+func (t *Ticker) Stop() { close(t.stop) }
+
+// NewTicker returns a new Ticker with a period of d.
+func NewTicker(d time.Duration) *Ticker {
+	c := make(chan time.Time) // unbuffered so we block and delay if not being handled
+	t := Ticker{C: c, stop: make(StopChan)}
+	go func() {
+		c <- time.Now()
+		for {
+			select {
+			case <-t.stop:
+				return
+
+			case <-time.After(utils.WithJitter(d)):
+				select {
+				case <-t.stop:
+					return
+				case c <- time.Now():
+				}
+			}
+		}
+	}()
+	return &t
+}