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/resizable_channel_test.go

@@ -0,0 +1,61 @@
+package channels
+
+import (
+	"math/rand"
+	"testing"
+)
+
+func TestResizableChannel(t *testing.T) {
+	var ch *ResizableChannel
+
+	ch = NewResizableChannel()
+	testChannel(t, "default resizable channel", ch)
+
+	ch = NewResizableChannel()
+	testChannelPair(t, "default resizable channel", ch, ch)
+
+	ch = NewResizableChannel()
+	ch.Resize(Infinity)
+	testChannel(t, "infinite resizable channel", ch)
+
+	ch = NewResizableChannel()
+	ch.Resize(Infinity)
+	testChannelPair(t, "infinite resizable channel", ch, ch)
+
+	ch = NewResizableChannel()
+	ch.Resize(5)
+	testChannel(t, "5-buffer resizable channel", ch)
+
+	ch = NewResizableChannel()
+	ch.Resize(5)
+	testChannelPair(t, "5-buffer resizable channel", ch, ch)
+
+	ch = NewResizableChannel()
+	testChannelConcurrentAccessors(t, "resizable channel", ch)
+}
+
+func TestResizableChannelOnline(t *testing.T) {
+	stopper := make(chan bool)
+	ch := NewResizableChannel()
+	go func() {
+		for i := 0; i < 1000; i++ {
+			ch.In() <- i
+		}
+		<-stopper
+		ch.Close()
+	}()
+
+	go func() {
+		for i := 0; i < 1000; i++ {
+			ch.Resize(BufferCap(rand.Intn(50) + 1))
+		}
+		close(stopper)
+	}()
+
+	for i := 0; i < 1000; i++ {
+		val := <-ch.Out()
+		if i != val.(int) {
+			t.Fatal("resizable channel expected", i, "but got", val.(int))
+		}
+	}
+}