feat: Concurrent chart download in template and lint commands

This enables `helmfile lint` and `helmfile template` commands to fetch and untar all the required charts concurrently. The concurrency is configurable via the `--concurrency` flag, that defaults to `0`.

Ref #292

main.go

@@ -202,6 +202,11 @@ func main() {
 					Name:  "values",
 					Usage: "additional value files to be merged into the command",
 				},
+				cli.IntFlag{
+					Name:  "concurrency",
+					Value: 0,
+					Usage: "maximum number of concurrent downloads of release charts",
+				},
 			},
 			Action: func(c *cli.Context) error {
 				return findAndIterateOverDesiredStatesUsingFlags(c, func(state *state.HelmState, helm helmexec.Interface) []error {
@@ -222,6 +227,11 @@ func main() {
 					Name:  "values",
 					Usage: "additional value files to be merged into the command",
 				},
+				cli.IntFlag{
+					Name:  "concurrency",
+					Value: 0,
+					Usage: "maximum number of concurrent downloads of release charts",
+				},
 			},
 			Action: func(c *cli.Context) error {
 				return findAndIterateOverDesiredStatesUsingFlags(c, func(state *state.HelmState, helm helmexec.Interface) []error {
@@ -231,8 +241,9 @@ func main() {
 
 					values := c.StringSlice("values")
 					args := args.GetArgs(c.String("args"), state)
+					workers := c.Int("concurrency")
 
-					return state.LintReleases(helm, values, args)
+					return state.LintReleases(helm, values, args, workers)
 				})
 			},
 		},
@@ -494,8 +505,9 @@ func executeTemplateCommand(c *cli.Context, state *state.HelmState, helm helmexe
 
 	args := args.GetArgs(c.String("args"), state)
 	values := c.StringSlice("values")
+	workers := c.Int("concurrency")
 
-	return state.TemplateReleases(helm, values, args)
+	return state.TemplateReleases(helm, values, args, workers)
 }
 
 func executeDiffCommand(c *cli.Context, st *state.HelmState, helm helmexec.Interface, detailedExitCode, suppressSecrets bool) ([]*state.ReleaseSpec, []error) {

state/state.go

@@ -272,10 +272,21 @@ func (state *HelmState) SyncReleases(helm helmexec.Interface, additionalValues [
 }
 
 // downloadCharts will download and untar charts for Lint and Template
-func (state *HelmState) downloadCharts(helm helmexec.Interface, dir string) (map[string]string, error) {
+func (state *HelmState) downloadCharts(helm helmexec.Interface, dir string, workerLimit int) (map[string]string, []error) {
 	temp := make(map[string]string, len(state.Releases))
+	errs := []error{}
 
-	for _, release := range state.Releases {
+	var wgFetch sync.WaitGroup
+	jobQueue := make(chan *ReleaseSpec, len(state.Releases))
+	wgFetch.Add(len(state.Releases))
+
+	if workerLimit < 1 {
+		workerLimit = len(state.Releases)
+	}
+
+	for w := 1; w <= workerLimit; w++ {
+		go func() {
+			for release := range jobQueue {
 				chartPath := ""
 				if pathExists(normalizeChart(state.basePath, release.Chart)) {
 					chartPath = normalizeChart(state.basePath, release.Chart)
@@ -292,19 +303,31 @@ func (state *HelmState) downloadCharts(helm helmexec.Interface, dir string) (map
 					if _, err := os.Stat(chartPath); os.IsNotExist(err) {
 						fetchFlags = append(fetchFlags, "--untar", "--untardir", chartPath)
 						if err := helm.Fetch(release.Chart, fetchFlags...); err != nil {
-					return nil, err
+							errs = append(errs, err)
 						}
 					}
 					chartPath = path.Join(chartPath, chartNameWithoutRepository(release.Chart))
 				}
 				temp[release.Name] = chartPath
+				wgFetch.Done()
+			}
+		}()
+	}
+	for i := 0; i < len(state.Releases); i++ {
+		jobQueue <- &state.Releases[i]
 	}
 
+	close(jobQueue)
+	wgFetch.Wait()
+
+	if len(errs) > 0 {
+		return nil, errs
+	}
 	return temp, nil
 }
 
 // TemplateReleases wrapper for executing helm template on the releases
-func (state *HelmState) TemplateReleases(helm helmexec.Interface, additionalValues []string, args []string) []error {
+func (state *HelmState) TemplateReleases(helm helmexec.Interface, additionalValues []string, args []string, workerLimit int) []error {
 	errs := []error{}
 	// Create tmp directory and bail immediately if it fails
 	dir, err := ioutil.TempDir("", "")
@@ -314,8 +337,9 @@ func (state *HelmState) TemplateReleases(helm helmexec.Interface, additionalValu
 	}
 	defer os.RemoveAll(dir)
 
-	temp, err := state.downloadCharts(helm, dir)
+	temp, errs := state.downloadCharts(helm, dir, workerLimit)
-	if err != nil {
+
+	if errs != nil {
 		errs = append(errs, err)
 		return errs
 	}
@@ -356,7 +380,7 @@ func (state *HelmState) TemplateReleases(helm helmexec.Interface, additionalValu
 }
 
 // LintReleases wrapper for executing helm lint on the releases
-func (state *HelmState) LintReleases(helm helmexec.Interface, additionalValues []string, args []string) []error {
+func (state *HelmState) LintReleases(helm helmexec.Interface, additionalValues []string, args []string, workerLimit int) []error {
 	errs := []error{}
 	// Create tmp directory and bail immediately if it fails
 	dir, err := ioutil.TempDir("", "")
@@ -366,8 +390,8 @@ func (state *HelmState) LintReleases(helm helmexec.Interface, additionalValues [
 	}
 	defer os.RemoveAll(dir)
 
-	temp, err := state.downloadCharts(helm, dir)
+	temp, errs := state.downloadCharts(helm, dir, workerLimit)
-	if err != nil {
+	if errs != nil {
 		errs = append(errs, err)
 		return errs
 	}