From adb87816f47d22196eb176092c671dbc1f1ea2da Mon Sep 17 00:00:00 2001
From: Julius Volz <julius@soundcloud.com>
Date: Wed, 5 Jun 2013 13:56:56 +0200
Subject: [PATCH] Put RuleManager concurrency in hands of caller, fix races.

---
 main.go          |  1 +
 rules/manager.go | 21 +++++++++++++++------
 2 files changed, 16 insertions(+), 6 deletions(-)

diff --git a/main.go b/main.go
index 3d84a45e9..282600e53 100644
--- a/main.go
+++ b/main.go
@@ -325,6 +325,7 @@ func main() {
 	if err != nil {
 		log.Fatalf("Error loading rule files: %v", err)
 	}
+	go ruleManager.Run()
 
 	go func() {
 		err := webService.ServeForever()
diff --git a/rules/manager.go b/rules/manager.go
index 0954fce25..fe32a60e4 100644
--- a/rules/manager.go
+++ b/rules/manager.go
@@ -29,10 +29,14 @@ type Result struct {
 
 type RuleManager interface {
 	AddRulesFromConfig(config config.Config) error
+	Run()
 }
 
 type ruleManager struct {
-	rules    []Rule
+	// Protects the rules list.
+	sync.Mutex
+	rules []Rule
+
 	results  chan *Result
 	done     chan bool
 	interval time.Duration
@@ -47,12 +51,10 @@ func NewRuleManager(results chan *Result, interval time.Duration, storage *metri
 		interval: interval,
 		storage:  storage,
 	}
-	// BUG(julius): Extract this so that the caller manages concurrency.
-	go manager.run(results)
 	return manager
 }
 
-func (m *ruleManager) run(results chan *Result) {
+func (m *ruleManager) Run() {
 	ticker := time.NewTicker(m.interval)
 	defer ticker.Stop()
 
@@ -60,7 +62,7 @@ func (m *ruleManager) run(results chan *Result) {
 		select {
 		case <-ticker.C:
 			start := time.Now()
-			m.runIteration(results)
+			m.runIteration(m.results)
 			evalDurations.Add(map[string]string{intervalKey: m.interval.String()}, float64(time.Since(start)/time.Millisecond))
 		case <-m.done:
 			log.Printf("RuleManager exiting...")
@@ -80,7 +82,12 @@ func (m *ruleManager) runIteration(results chan *Result) {
 	now := time.Now()
 	wg := sync.WaitGroup{}
 
-	for _, rule := range m.rules {
+	m.Lock()
+	rules := make([]Rule, len(m.rules))
+	copy(rules, m.rules)
+	m.Unlock()
+
+	for _, rule := range rules {
 		wg.Add(1)
 		// BUG(julius): Look at fixing thundering herd.
 		go func(rule Rule) {
@@ -104,7 +111,9 @@ func (m *ruleManager) AddRulesFromConfig(config config.Config) error {
 		if err != nil {
 			return err
 		}
+		m.Lock()
 		m.rules = append(m.rules, newRules...)
+		m.Unlock()
 	}
 	return nil
 }