Add concurrency limiting semaphore

drive-demuxer.go

@@ -16,6 +16,7 @@ type TopLevel struct {
 	LeftOutput     string
 	CombinedOutput string
 	RightOutput    string
+	OpenHandles    chan int
 }
 
 type Step struct {
@@ -181,7 +182,7 @@ func (s *Step) ListChildren() []string {
 		results[file.Name()] = true
 	}
 	out := make([]string, 0, len(results))
-	for file, _ := range results {
+	for file := range results {
 		out = append(out, file)
 	}
 	return out
@@ -298,7 +299,11 @@ func (s *Step) Walk() {
 				}
 				wg.Add(1)
 				go func() {
-					defer func() { wg.Done() }()
+					defer func() {
+						<-s.OpenHandles
+						wg.Done()
+					}()
+					s.OpenHandles <- 1
 					substep.Walk()
 					s.RemoveInputDirs(child)
 				}()
@@ -314,7 +319,9 @@ func (s *Step) Walk() {
 }
 
 func main() {
-	settings := TopLevel{}
+	settings := TopLevel{
+		OpenHandles: make(chan int, 300),
+	}
 	flag.StringVar(&settings.LeftInput,
 		"left-input", "./input/left", "The name of the left side of the input.")
 	flag.StringVar(&settings.RightInput,