From 770c16a66d008f4e33af5efbade73c55e87c4310 Mon Sep 17 00:00:00 2001
From: Asim Aslam <asim@aslam.me>
Date: Tue, 18 Dec 2018 16:51:42 +0000
Subject: [PATCH] move to using rwmutex for selector

---
 selector/cache/cache.go | 49 ++++++++++++++++++++++++++++++++---------
 1 file changed, 38 insertions(+), 11 deletions(-)

diff --git a/selector/cache/cache.go b/selector/cache/cache.go
index 482c068b..b89a9bef 100644
--- a/selector/cache/cache.go
+++ b/selector/cache/cache.go
@@ -15,7 +15,7 @@ type cacheSelector struct {
 	ttl time.Duration
 
 	// registry cache
-	sync.Mutex
+	sync.RWMutex
 	cache map[string][]*registry.Service
 	ttls  map[string]time.Time
 
@@ -81,13 +81,12 @@ func (c *cacheSelector) del(service string) {
 }
 
 func (c *cacheSelector) get(service string) ([]*registry.Service, error) {
-	c.Lock()
-	defer c.Unlock()
+	// read lock for the duration
+	c.RLock()
 
 	// watch service if not watched
 	if _, ok := c.watched[service]; !ok {
 		go c.run(service)
-		c.watched[service] = true
 	}
 
 	// get does the actual request for a service
@@ -100,15 +99,24 @@ func (c *cacheSelector) get(service string) ([]*registry.Service, error) {
 		}
 
 		// cache results
+		c.Lock()
 		c.set(service, c.cp(services))
+		c.Unlock()
+
 		return services, nil
 	}
 
 	// check the cache first
 	services, ok := c.cache[service]
+	// make a copy
+	cp := c.cp(services)
 
 	// cache miss or no services
 	if !ok || len(services) == 0 {
+		// unlock the read
+		c.RUnlock()
+
+		// get and return services
 		return get(service)
 	}
 
@@ -117,15 +125,22 @@ func (c *cacheSelector) get(service string) ([]*registry.Service, error) {
 
 	// within ttl so return cache
 	if kk && time.Since(ttl) < c.ttl {
-		return c.cp(services), nil
+		// unlock the read
+		c.RUnlock()
+
+		// return servics
+		return cp, nil
 	}
 
-	// expired entry so get service
-	services, err := get(service)
+	// unlock read
+	c.RUnlock()
 
-	// no error then return error
+	// expired entry so get service
+	rservices, err := get(service)
+
+	// no error then return services
 	if err == nil {
-		return services, nil
+		return rservices, nil
 	}
 
 	// not found error then return
@@ -135,8 +150,8 @@ func (c *cacheSelector) get(service string) ([]*registry.Service, error) {
 
 	// other error
 
-	// return expired cache as last resort
-	return c.cp(services), nil
+	// return expired cache copy as last resort
+	return cp, nil
 }
 
 func (c *cacheSelector) set(service string, services []*registry.Service) {
@@ -257,6 +272,18 @@ func (c *cacheSelector) update(res *registry.Result) {
 // reloads the watcher if Init is called
 // and returns when Close is called
 func (c *cacheSelector) run(name string) {
+	// set watcher
+	c.Lock()
+	c.watched[name] = true
+	c.Unlock()
+
+	// delete watcher on exit
+	defer func() {
+		c.Lock()
+		delete(c.watched, name)
+		c.Unlock()
+	}()
+
 	for {
 		// exit early if already dead
 		if c.quit() {