Get container stats directly for oneshot

Signed-off-by: Xinfeng Liu <XinfengLiu@icloud.com>

daemon/stats.go

@@ -43,6 +43,15 @@ func (daemon *Daemon) ContainerStats(ctx context.Context, prefixOrName string, c
 		})
 	}
 
+	// Get container stats directly if OneShot is set
+	if config.OneShot {
+		stats, err := daemon.statsCollector.CollectOneShot(ctr)
+		if err != nil {
+			return err
+		}
+		return json.NewEncoder(config.OutStream).Encode(stats)
+	}
+
 	outStream := config.OutStream
 	if config.Stream {
 		wf := ioutils.NewWriteFlusher(outStream)

daemon/stats/collector.go

@@ -21,6 +21,12 @@ type Collector struct {
 	supervisor supervisor
 	interval   time.Duration
 	publishers map[*container.Container]*pubsub.Publisher
+	sync.RWMutex
+	cache cache
+}
+
+type cache struct {
+	onlineCPUs uint32
 }
 
 // NewCollector creates a stats collector that will poll the supervisor with the specified interval
@@ -56,6 +62,11 @@ func (s *Collector) Collect(c *container.Container) chan interface{} {
 	return publisher.Subscribe()
 }
 
+// CollectOneShot collect one shot container stats
+func (s *Collector) CollectOneShot(c *container.Container) (*types.StatsJSON, error) {
+	return s.getContainerStats(c)
+}
+
 // StopCollection closes the channels for all subscribers and removes
 // the container from metrics collection.
 func (s *Collector) StopCollection(c *container.Container) {
@@ -114,6 +125,9 @@ func (s *Collector) Run() {
 			time.Sleep(s.interval)
 			continue
 		}
+		s.Lock()
+		s.cache.onlineCPUs = onlineCPUs
+		s.Unlock()
 
 		g, ctx := errgroup.WithContext(context.Background())
 		pairCh := make(chan publishersPair)
@@ -138,38 +152,11 @@ func (s *Collector) Run() {
 		for i := 0; i < numWorkers; i++ {
 			g.Go(func() error {
 				for pair := range pairCh {
-					stats, err := s.supervisor.GetContainerStats(pair.container)
-
-					switch err.(type) {
-					case nil:
-						// Sample system CPU usage close to container usage to avoid
-						// noise in metric calculations.
-						systemUsage, err := s.getSystemCPUUsage()
-						if err != nil {
-							log.G(context.TODO()).WithError(err).WithField("container_id", pair.container.ID).Errorf("collecting system cpu usage")
-							return err
-						}
-
-						// FIXME: move to containerd on Linux (not Windows)
-						stats.CPUStats.SystemUsage = systemUsage
-						stats.CPUStats.OnlineCPUs = onlineCPUs
-
-						pair.publisher.Publish(*stats)
-
-					case errdefs.ErrConflict, errdefs.ErrNotFound:
-						// publish empty stats containing only name and ID if not running or not found
-						pair.publisher.Publish(types.StatsJSON{
-							Name: pair.container.Name,
-							ID:   pair.container.ID,
-						})
-
-					default:
-						log.G(context.TODO()).Errorf("collecting stats for %s: %v", pair.container.ID, err)
-						pair.publisher.Publish(types.StatsJSON{
-							Name: pair.container.Name,
-							ID:   pair.container.ID,
-						})
+					stats, err := s.getContainerStats(pair.container)
+					if err != nil {
+						return err
 					}
+					pair.publisher.Publish(*stats)
 
 					select {
 					case <-ctx.Done():
@@ -184,3 +171,35 @@ func (s *Collector) Run() {
 		time.Sleep(s.interval)
 	}
 }
+
+func (s *Collector) getContainerStats(c *container.Container) (*types.StatsJSON, error) {
+	stats, err := s.supervisor.GetContainerStats(c)
+	switch err.(type) {
+	case nil:
+		// Sample system CPU usage close to container usage to avoid
+		// noise in metric calculations.
+		systemUsage, err := s.getSystemCPUUsage()
+		if err != nil {
+			log.G(context.TODO()).WithError(err).WithField("container_id", c.ID).Errorf("collecting system cpu usage")
+			return nil, err
+		}
+		// FIXME: move to containerd on Linux (not Windows)
+		stats.CPUStats.SystemUsage = systemUsage
+		s.RLock()
+		stats.CPUStats.OnlineCPUs = s.cache.onlineCPUs
+		s.RUnlock()
+		return stats, nil
+	case errdefs.ErrConflict, errdefs.ErrNotFound:
+		// publish empty stats containing only name and ID if not running or not found
+		return &types.StatsJSON{
+			Name: c.Name,
+			ID:   c.ID,
+		}, nil
+	default:
+		log.G(context.TODO()).Errorf("collecting stats for %s: %v", c.ID, err)
+		return &types.StatsJSON{
+			Name: c.Name,
+			ID:   c.ID,
+		}, nil
+	}
+}