Add thumbnail cache

transcoder/main.go

@@ -264,7 +264,7 @@ func (h *Handler) GetSubtitle(c echo.Context) error {
 
 // Get thumbnail sprite
 //
-// Get a sprite file containing all the thumbnails of the show
+// Get a sprite file containing all the thumbnails of the show.
 //
 // Path: /:resource/:slug/thumbnails.png
 func (h *Handler) GetThumbnails(c echo.Context) error {
@@ -276,7 +276,10 @@ func (h *Handler) GetThumbnails(c echo.Context) error {
 		return err
 	}
 
-	out, err := src.ExtractThumbnail(path)
+	out, err := h.thumbnails.ExtractThumbnail(
+		path,
+		fmt.Sprintf("%s/%s/thumbnails.png", resource, slug),
+	)
 	if err != nil {
 		return err
 	}
@@ -299,7 +302,10 @@ func (h *Handler) GetThumbnailsVtt(c echo.Context) error {
 		return err
 	}
 
-	out, err := src.ExtractThumbnail(path)
+	out, err := h.thumbnails.ExtractThumbnail(
+		path,
+		fmt.Sprintf("%s/%s/thumbnails.png", resource, slug),
+	)
 	if err != nil {
 		return err
 	}
@@ -310,6 +316,7 @@ func (h *Handler) GetThumbnailsVtt(c echo.Context) error {
 type Handler struct {
 	transcoder *src.Transcoder
 	extractor  *src.Extractor
+	thumbnails *src.ThumbnailsCreator
 }
 
 func main() {
@@ -322,7 +329,11 @@ func main() {
 		e.Logger.Fatal(err)
 		return
 	}
-	h := Handler{transcoder: transcoder, extractor: src.NewExtractor()}
+	h := Handler{
+		transcoder: transcoder,
+		extractor:  src.NewExtractor(),
+		thumbnails: src.NewThumbnailsCreator(),
+	}
 
 	e.GET("/:resource/:slug/direct", DirectStream)
 	e.GET("/:resource/:slug/master.m3u8", h.GetMaster)

transcoder/src/thumbnails.go

@@ -7,6 +7,7 @@ import (
 	"log"
 	"math"
 	"os"
+	"sync"
 
 	"github.com/disintegration/imaging"
 	"gitlab.com/opennota/screengen"
@@ -15,7 +16,53 @@ import (
 // We want to have a thumbnail every ${interval} seconds.
 var default_interval = 10
 
-func ExtractThumbnail(path string) (string, error) {
+type ThumbnailsCreator struct {
+	created map[string]string
+	running map[string]chan struct{}
+	lock    sync.Mutex
+}
+
+func NewThumbnailsCreator() *ThumbnailsCreator {
+	return &ThumbnailsCreator{
+		created: make(map[string]string),
+		running: make(map[string]chan struct{}),
+	}
+}
+
+func (t *ThumbnailsCreator) ExtractThumbnail(path string, name string) (string, error) {
+	t.lock.Lock()
+	defer t.lock.Unlock()
+
+	out, ok := t.created[path]
+	if ok {
+		return out, nil
+	}
+
+	wait, ok := t.running[path]
+	if ok {
+		t.lock.Unlock()
+		<-wait
+		t.lock.Lock()
+		out = t.created[path]
+		return out, nil
+	}
+	wait = make(chan struct{})
+	t.running[path] = wait
+
+	t.lock.Unlock()
+
+	out, err := extractThumbnail(path, name)
+	t.lock.Lock()
+	// this will be unlocked by the defer at the top of the function.
+
+	delete(t.running, path)
+	if err == nil {
+		t.created[path] = out
+	}
+	return out, err
+}
+
+func extractThumbnail(path string, name string) (string, error) {
 	ret, err := GetInfo(path)
 	if err != nil {
 		return "", err