feat(util/delay) add Delay

License: MIT
Signed-off-by: Brian Tiger Chow <brian@perfmode.com>

util/delay/delay.go

+package delay
+
+import (
+	"sync"
+	"time"
+)
+
+// Delay makes it easy to add (threadsafe) configurable delays to other
+// objects.
+type D interface {
+	Set(time.Duration) time.Duration
+	Wait()
+}
+
+// Fixed returns a delay with fixed latency
+func Fixed(t time.Duration) D {
+	return &delay{t: t}
+}
+
+type delay struct {
+	l sync.RWMutex
+	t time.Duration
+}
+
+// TODO func Variable(time.Duration) D returns a delay with probablistic latency
+
+func (d *delay) Set(t time.Duration) time.Duration {
+	d.l.Lock()
+	defer d.l.Unlock()
+	prev := d.t
+	d.t = t
+	return prev
+}
+
+func (d *delay) Wait() {
+	d.l.RLock()
+	defer d.l.RUnlock()
+	time.Sleep(d.t)
+}