From 378cd81dbe7b239d56df466b85c1542839b6251e Mon Sep 17 00:00:00 2001
From: Wojciech Tyczynski <wojtekt@google.com>
Date: Thu, 8 Sep 2016 12:02:27 +0200
Subject: [PATCH] Split dispatching to watchers in Cacher into separate
 goroutine.

---
 pkg/storage/cacher.go | 38 ++++++++++++++++++++++++++++----------
 1 file changed, 28 insertions(+), 10 deletions(-)

diff --git a/pkg/storage/cacher.go b/pkg/storage/cacher.go
index dcd88cbc44a..cacb34f6339 100644
--- a/pkg/storage/cacher.go
+++ b/pkg/storage/cacher.go
@@ -161,6 +161,9 @@ type Cacher struct {
 	watcherIdx int
 	watchers   indexedWatchers
 
+	// Incoming events that should be dispatched to watchers.
+	incoming chan watchCacheEvent
+
 	// Handling graceful termination.
 	stopLock sync.RWMutex
 	stopped  bool
@@ -197,6 +200,8 @@ func NewCacherFromConfig(config CacherConfig) *Cacher {
 			allWatchers:   make(map[int]*cacheWatcher),
 			valueWatchers: make(map[string]watchersMap),
 		},
+		// TODO: Figure out the correct value for the buffer size.
+		incoming: make(chan watchCacheEvent, 100),
 		// We need to (potentially) stop both:
 		// - wait.Until go-routine
 		// - reflector.ListAndWatch
@@ -205,6 +210,7 @@ func NewCacherFromConfig(config CacherConfig) *Cacher {
 		stopCh: make(chan struct{}),
 	}
 	watchCache.SetOnEvent(cacher.processEvent)
+	go cacher.dispatchEvents()
 
 	stopCh := cacher.stopCh
 	cacher.stopWg.Add(1)
@@ -403,14 +409,26 @@ func (c *Cacher) triggerValues(event *watchCacheEvent) ([]string, bool) {
 	return result, len(result) > 0
 }
 
-// TODO: Most probably splitting this method to a separate thread will visibily
-// improve throughput of our watch machinery. So what we should do is to:
-// - OnEvent handler simply put an element to channel
-// - processEvent be another goroutine processing events from that channel
-// Additionally, if we make this channel buffered, cacher will be more resistant
-// to single watchers being slow - see cacheWatcher::add method.
 func (c *Cacher) processEvent(event watchCacheEvent) {
-	triggerValues, supported := c.triggerValues(&event)
+	c.incoming <- event
+}
+
+func (c *Cacher) dispatchEvents() {
+	for {
+		select {
+		case event, ok := <-c.incoming:
+			if !ok {
+				return
+			}
+			c.dispatchEvent(&event)
+		case <-c.stopCh:
+			return
+		}
+	}
+}
+
+func (c *Cacher) dispatchEvent(event *watchCacheEvent) {
+	triggerValues, supported := c.triggerValues(event)
 
 	c.Lock()
 	defer c.Unlock()
@@ -614,10 +632,10 @@ func (c *cacheWatcher) stop() {
 
 var timerPool sync.Pool
 
-func (c *cacheWatcher) add(event watchCacheEvent) {
+func (c *cacheWatcher) add(event *watchCacheEvent) {
 	// Try to send the event immediately, without blocking.
 	select {
-	case c.input <- event:
+	case c.input <- *event:
 		return
 	default:
 	}
@@ -636,7 +654,7 @@ func (c *cacheWatcher) add(event watchCacheEvent) {
 	defer timerPool.Put(t)
 
 	select {
-	case c.input <- event:
+	case c.input <- *event:
 		stopped := t.Stop()
 		if !stopped {
 			// Consume triggered (but not yet received) timer event