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/ring_channel_test.go

@@ -0,0 +1,49 @@
+package channels
+
+import "testing"
+
+func TestRingChannel(t *testing.T) {
+	var ch Channel
+
+	ch = NewRingChannel(Infinity) // yes this is rather silly, but it should work
+	testChannel(t, "infinite ring-buffer channel", ch)
+
+	ch = NewRingChannel(None)
+	go func() {
+		for i := 0; i < 1000; i++ {
+			ch.In() <- i
+		}
+		ch.Close()
+	}()
+	prev := -1
+	for i := range ch.Out() {
+		if prev >= i.(int) {
+			t.Fatal("ring channel prev", prev, "but got", i.(int))
+		}
+	}
+
+	ch = NewRingChannel(10)
+	for i := 0; i < 1000; i++ {
+		ch.In() <- i
+	}
+	ch.Close()
+	for i := 990; i < 1000; i++ {
+		val := <-ch.Out()
+		if i != val.(int) {
+			t.Fatal("ring channel expected", i, "but got", val.(int))
+		}
+	}
+	if val, open := <-ch.Out(); open == true {
+		t.Fatal("ring channel expected closed but got", val)
+	}
+
+	ch = NewRingChannel(None)
+	ch.In() <- 0
+	ch.Close()
+	if val, open := <-ch.Out(); open == true {
+		t.Fatal("ring channel expected closed but got", val)
+	}
+
+	ch = NewRingChannel(2)
+	testChannelConcurrentAccessors(t, "ring channel", ch)
+}