Add a concurrency limit

1 files changed, 17 insertions, 12 deletions

diff --git a/ils.go b/ils.go
index 05ece82..71701c9 100644
--- a/ils.go
+++ b/ils.go
@@ -204,19 +204,24 @@ func thumbnailFiles(w io.Writer, imagePaths []string, width, rowWidth, cellX, ce
 		rowImages[i] = make(chan image.Image, 1)
 	}
 	errCh := make(chan error, 1)
-	for i, row := range rows {
-		go func() {
-			img, err := compositeImageRow(row, width*cellX, rowWidth*cellX, cellX, aspectRatio)
-			if err != nil {
-				select {
-				case errCh <- err:
-				default:
+	go func() {
+		sem := make(chan struct{}, 20)
+		for i, row := range rows {
+			sem <- struct{}{}
+			go func() {
+				defer func() { <-sem }()
+				img, err := compositeImageRow(row, width*cellX, rowWidth*cellX, cellX, aspectRatio)
+				if err != nil {
+					select {
+					case errCh <- err:
+					default:
+					}
+					return
 				}
-				return
-			}
-			rowImages[i] <- img
-		}()
-	}
+				rowImages[i] <- img
+			}()
+		}
+	}()
 	for i, row := range rows {
 		thisRowWidth := 0
 		for j, filename := range row {