Use a ring channel to avoid blocking write of events (#2082)

* Use a ring channel to avoid blocking write of events

* Add eapache/channels dependency

vendor/github.com/eapache/channels/black_hole.go

@@ -0,0 +1,54 @@
+package channels
+
+// BlackHole implements the InChannel interface and provides an analogue for the "Discard" variable in
+// the ioutil package - it never blocks, and simply discards every value it reads. The number of items
+// discarded in this way is counted and returned from Len.
+type BlackHole struct {
+	input  chan interface{}
+	length chan int
+	count  int
+}
+
+func NewBlackHole() *BlackHole {
+	ch := &BlackHole{
+		input:  make(chan interface{}),
+		length: make(chan int),
+	}
+	go ch.discard()
+	return ch
+}
+
+func (ch *BlackHole) In() chan<- interface{} {
+	return ch.input
+}
+
+func (ch *BlackHole) Len() int {
+	val, open := <-ch.length
+	if open {
+		return val
+	} else {
+		return ch.count
+	}
+}
+
+func (ch *BlackHole) Cap() BufferCap {
+	return Infinity
+}
+
+func (ch *BlackHole) Close() {
+	close(ch.input)
+}
+
+func (ch *BlackHole) discard() {
+	for {
+		select {
+		case _, open := <-ch.input:
+			if !open {
+				close(ch.length)
+				return
+			}
+			ch.count++
+		case ch.length <- ch.count:
+		}
+	}
+}