stats refactor

Refactor the entities' stats API to simplify using it and reduce the
risk of running into concurrency issues at the call sites.  Further
simplify the stats code by de-spaghetti-ing the logic and reducing
duplicate code.

`ContainerStats` now returns a data channel and an error.  If the error
is nil, callers can read from the channel.

Signed-off-by: Valentin Rothberg <rothberg@redhat.com>

1 files changed, 18 insertions, 20 deletions

diff --git a/cmd/podman/containers/stats.go b/cmd/podman/containers/stats.go
index ddb5f32ef..1a4adb376 100644
--- a/cmd/podman/containers/stats.go
+++ b/cmd/podman/containers/stats.go
@@ -4,7 +4,6 @@ import (
 	"fmt"
 	"os"
 	"strings"
-	"sync"
 	"text/tabwriter"
 	"text/template"
 
@@ -107,32 +106,31 @@ func stats(cmd *cobra.Command, args []string) error {
 			return errors.New("stats is not supported in rootless mode without cgroups v2")
 		}
 	}
-	statsOptions.StatChan = make(chan []*define.ContainerStats, 1)
-	wg := sync.WaitGroup{}
-	wg.Add(1)
-	go func() {
-		for reports := range statsOptions.StatChan {
-			if err := outputStats(reports); err != nil {
-				logrus.Error(err)
-			}
-		}
-		wg.Done()
 
-	}()
-	err := registry.ContainerEngine().ContainerStats(registry.Context(), args, statsOptions)
-	wg.Wait()
-	return err
+	statsChan, err := registry.ContainerEngine().ContainerStats(registry.Context(), args, statsOptions)
+	if err != nil {
+		return err
+	}
+	for report := range statsChan {
+		if report.Error != nil {
+			return report.Error
+		}
+		if err := outputStats(report.Stats); err != nil {
+			logrus.Error(err)
+		}
+	}
+	return nil
 }
 
-func outputStats(reports []*define.ContainerStats) error {
+func outputStats(reports []define.ContainerStats) error {
 	if len(statsOptions.Format) < 1 && !statsOptions.NoReset {
 		tm.Clear()
 		tm.MoveCursor(1, 1)
 		tm.Flush()
 	}
-	stats := make([]*containerStats, 0, len(reports))
+	stats := make([]containerStats, 0, len(reports))
 	for _, r := range reports {
-		stats = append(stats, &containerStats{r})
+		stats = append(stats, containerStats{r})
 	}
 	if statsOptions.Format == "json" {
 		return outputJSON(stats)
@@ -163,7 +161,7 @@ func outputStats(reports []*define.ContainerStats) error {
 }
 
 type containerStats struct {
-	*define.ContainerStats
+	define.ContainerStats
 }
 
 func (s *containerStats) ID() string {
@@ -213,7 +211,7 @@ func combineHumanValues(a, b uint64) string {
 	return fmt.Sprintf("%s / %s", units.HumanSize(float64(a)), units.HumanSize(float64(b)))
 }
 
-func outputJSON(stats []*containerStats) error {
+func outputJSON(stats []containerStats) error {
 	type jstat struct {
 		Id         string `json:"id"` //nolint
 		Name       string `json:"name"`