engine: Added a concurrent safe refresh delayer.

Signed-off-by: Andrea Luzzardi <aluzzardi@gmail.com>

cluster/engine.go

@@ -21,8 +21,8 @@ import (
 
 const (
 	// Force-refresh the state of the engine this often.
-	stateRefreshMinRange = 30
-	stateRefreshMaxRange = 60
+	stateRefreshMinRange = 30 * time.Second
+	stateRefreshMaxRange = 60 * time.Second
 	stateRefreshRetries  = 3
 
 	// Timeout for requests sent out to the engine.
@@ -32,20 +32,29 @@ const (
 	minSupportedVersion = version.Version("1.6.0")
 )
 
-// NewEngine is exported
-func NewEngine(addr string, overcommitRatio float64) *Engine {
-	e := &Engine{
-		Addr:            addr,
-		client:          nopclient.NewNopClient(),
-		Labels:          make(map[string]string),
-		stopCh:          make(chan struct{}),
-		r:               rand.New(rand.NewSource(time.Now().UTC().UnixNano())),
-		containers:      make(map[string]*Container),
-		volumes:         make(map[string]*Volume),
-		healthy:         true,
-		overcommitRatio: int64(overcommitRatio * 100),
+// delayer offers a simple API to random delay within a given time range.
+type delayer struct {
+	rangeMin time.Duration
+	rangeMax time.Duration
+
+	r *rand.Rand
+	l sync.Mutex
+}
+
+func newDelayer(rangeMin, rangeMax time.Duration) *delayer {
+	return &delayer{
+		rangeMin: rangeMin,
+		rangeMax: rangeMax,
+		r:        rand.New(rand.NewSource(time.Now().UTC().UnixNano())),
 	}
-	return e
+}
+
+func (d *delayer) Wait() <-chan time.Time {
+	d.l.Lock()
+	defer d.l.Unlock()
+
+	waitPeriod := int64(d.rangeMin) + d.r.Int63n(int64(d.rangeMax)-int64(d.rangeMin))
+	return time.After(time.Duration(waitPeriod))
 }
 
 // Engine represents a docker engine
@@ -61,7 +70,7 @@ type Engine struct {
 	Labels map[string]string
 
 	stopCh          chan struct{}
-	r               *rand.Rand
+	refreshDelayer  *delayer
 	containers      map[string]*Container
 	images          []*Image
 	volumes         map[string]*Volume
@@ -71,6 +80,22 @@ type Engine struct {
 	overcommitRatio int64
 }
 
+// NewEngine is exported
+func NewEngine(addr string, overcommitRatio float64) *Engine {
+	e := &Engine{
+		Addr:            addr,
+		client:          nopclient.NewNopClient(),
+		refreshDelayer:  newDelayer(stateRefreshMinRange, stateRefreshMaxRange),
+		Labels:          make(map[string]string),
+		stopCh:          make(chan struct{}),
+		containers:      make(map[string]*Container),
+		volumes:         make(map[string]*Volume),
+		healthy:         true,
+		overcommitRatio: int64(overcommitRatio * 100),
+	}
+	return e
+}
+
 // Connect will initialize a connection to the Docker daemon running on the
 // host, gather machine specs (memory, cpu, ...) and monitor state changes.
 func (e *Engine) Connect(config *tls.Config) error {
@@ -346,11 +371,9 @@ func (e *Engine) refreshLoop() {
 	for {
 		var err error
 
-		refreshPeriod := time.Duration(e.r.Intn(stateRefreshMaxRange-stateRefreshMinRange) + stateRefreshMinRange)
-
-		// Sleep stateRefreshPeriod or quit if we get stopped.
+		// Wait for the delayer or quit if we get stopped.
 		select {
-		case <-time.After(refreshPeriod * time.Second):
+		case <-e.refreshDelayer.Wait():
 		case <-e.stopCh:
 			return
 		}