feat(transcode): lock the destination transcode cache path

transcode/transcode_test.go

@@ -2,11 +2,14 @@ package transcode_test
 
 import (
 	"bytes"
+	"context"
 	"io"
 	"net/http"
 	"net/http/httptest"
 	"os"
 	"os/exec"
+	"sync"
+	"sync/atomic"
 	"testing"
 	"time"
 
@@ -100,3 +103,41 @@ func TestTranscodeWithSeek(t *testing.T) {
 	// since we seeked 2 seconds, we should have 5-2 = 3 seconds of PCM data
 	require.Equal(t, (testFileLen-seekSecs)*bytesPerSec, buf.Len())
 }
+
+func TestCachingParallelism(t *testing.T) {
+	t.Parallel()
+
+	var realTranscodeCount atomic.Uint64
+	transcoder := callbackTranscoder{
+		transcoder: transcode.NewFFmpegTranscoder(),
+		callback:   func() { realTranscodeCount.Add(1) },
+	}
+
+	cacheTranscoder := transcode.NewCachingTranscoder(transcoder, t.TempDir())
+
+	var wg sync.WaitGroup
+	for i := 0; i < 5; i++ {
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+
+			var buf bytes.Buffer
+			require.NoError(t, cacheTranscoder.Transcode(context.Background(), transcode.PCM16le, "testdata/5s.flac", &buf))
+			require.Equal(t, 5*bytesPerSec, buf.Len())
+		}()
+	}
+
+	wg.Wait()
+
+	require.Equal(t, 1, int(realTranscodeCount.Load()))
+}
+
+type callbackTranscoder struct {
+	transcoder transcode.Transcoder
+	callback   func()
+}
+
+func (ct callbackTranscoder) Transcode(ctx context.Context, profile transcode.Profile, in string, out io.Writer) error {
+	ct.callback()
+	return ct.transcoder.Transcode(ctx, profile, in, out)
+}