renderer: copy cache path before render to avoid race conditions

app/render/backend/renderbackend.cpp

@@ -430,7 +430,7 @@ void RenderBackend::RunNextJob()
       worker->SetRenderMode(render_mode_);
       worker->SetPreviewGenerationEnabled(generate_audio_previews_);
       worker->SetCopyMap(&copy_map_);
-      worker->SetViewerNode(viewer_node_);
+      worker->SetCachePath(viewer_node_->video_frame_cache()->GetCacheDirectory());
 
       // Move ticket from queue to running list
       RenderTicketPtr ticket = render_queue_.front();

app/render/backend/renderworker.cpp

@@ -318,10 +318,11 @@ QVariant RenderWorker::ProcessFrameGeneration(const Node* node, const GenerateJo
 QVariant RenderWorker::GetCachedFrame(const Node* node, const rational& time)
 {
   if (render_mode_ == RenderMode::kOffline
+      && !cache_path_.isEmpty()
       && node->id() == QStringLiteral("org.olivevideoeditor.Olive.videoinput")) {
     QByteArray hash = HashNode(node, video_params(), time);
 
-    FramePtr f = viewer_->video_frame_cache()->LoadCacheFrame(hash);
+    FramePtr f = FrameHashCache::LoadCacheFrame(cache_path_, hash);
 
     if (f) {
       // The cached frame won't load with the correct divider by default, so we enforce it here

app/render/backend/renderworker.h

@@ -50,11 +50,6 @@ public:
     available_ = a;
   }
 
-  void SetViewerNode(ViewerOutput* viewer)
-  {
-    viewer_ = viewer;
-  }
-
   void SetVideoParams(const VideoParams& params)
   {
     video_params_ = params;
@@ -90,6 +85,11 @@ public:
     generate_audio_previews_ = e;
   }
 
+  void SetCachePath(const QString& s)
+  {
+    cache_path_ = s;
+  }
+
   void Hash(RenderTicketPtr ticket, ViewerOutput* viewer, const QVector<rational>& times);
 
   /**
@@ -186,14 +186,14 @@ private:
 
   bool generate_audio_previews_;
 
-  ViewerOutput* viewer_;
-
   QHash<Node*, Node*>* copy_map_;
 
   RenderMode::Mode render_mode_;
 
   QTimer* cleanup_timer_;
 
+  QString cache_path_;
+
   static const int kMaxDecoderLife;
 
 private slots: