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/infinite_channel.go

@@ -0,0 +1,72 @@
+package channels
+
+import "github.com/eapache/queue"
+
+// InfiniteChannel implements the Channel interface with an infinite buffer between the input and the output.
+type InfiniteChannel struct {
+	input, output chan interface{}
+	length        chan int
+	buffer        *queue.Queue
+}
+
+func NewInfiniteChannel() *InfiniteChannel {
+	ch := &InfiniteChannel{
+		input:  make(chan interface{}),
+		output: make(chan interface{}),
+		length: make(chan int),
+		buffer: queue.New(),
+	}
+	go ch.infiniteBuffer()
+	return ch
+}
+
+func (ch *InfiniteChannel) In() chan<- interface{} {
+	return ch.input
+}
+
+func (ch *InfiniteChannel) Out() <-chan interface{} {
+	return ch.output
+}
+
+func (ch *InfiniteChannel) Len() int {
+	return <-ch.length
+}
+
+func (ch *InfiniteChannel) Cap() BufferCap {
+	return Infinity
+}
+
+func (ch *InfiniteChannel) Close() {
+	close(ch.input)
+}
+
+func (ch *InfiniteChannel) infiniteBuffer() {
+	var input, output chan interface{}
+	var next interface{}
+	input = ch.input
+
+	for input != nil || output != nil {
+		select {
+		case elem, open := <-input:
+			if open {
+				ch.buffer.Add(elem)
+			} else {
+				input = nil
+			}
+		case output <- next:
+			ch.buffer.Remove()
+		case ch.length <- ch.buffer.Length():
+		}
+
+		if ch.buffer.Length() > 0 {
+			output = ch.output
+			next = ch.buffer.Peek()
+		} else {
+			output = nil
+			next = nil
+		}
+	}
+
+	close(ch.output)
+	close(ch.length)
+}