rendertask: limit maximum frames that can be rendered concurrently

Fixes #1418

app/task/render/render.cpp

@@ -72,6 +72,7 @@ bool RenderTask::Render(ColorManager* manager,
 
   // Look up hashes
   QMap<QByteArray, QVector<rational> > time_map;
+  QVector<QPair<rational, QByteArray> > frame_render_order;
 
   if (!video_range.isEmpty()) {
     // Get list of discrete frames from range
@@ -95,21 +96,11 @@ bool RenderTask::Render(ColorManager* manager,
 
       const QByteArray& hash = hashes.at(i);
 
-      time_map[hash].append(times.at(i));
+      QVector<rational>& hash_time_list = time_map[hash];
+      hash_time_list.append(times.at(i));
 
-      if (time_map[hash].size() == 1) {
-        // This is the first frame with this hash, so we signal a render
-        RenderTicketWatcher* watcher = new RenderTicketWatcher();
-        watcher->setProperty("hash", hash);
-        PrepareWatcher(watcher, &watcher_thread);
-
-        IncrementRunningTickets();
-
-        watcher->SetTicket(RenderManager::instance()->RenderFrame(viewer_, manager, times.at(i),
-                                                                  mode, video_params_, audio_params_,
-                                                                  force_size, force_matrix,
-                                                                  force_format, force_color_output,
-                                                                  cache));
+      if (hash_time_list.size() == 1) {
+        frame_render_order.append({times.at(i), hash});
       }
     }
 
@@ -117,6 +108,18 @@ bool RenderTask::Render(ColorManager* manager,
     total_length += video_frame_sz * time_map.size();
   }
 
+  // Start a render of a limited amount, and then render one frame for each frame that gets
+  // finished. This prevents rendered frames from stacking up in memory indefinitely while the
+  // encoder is processing them. The amount is kind of arbitrary, but we use the thread count so
+  // each of the system's threads are utilized as memory allows.
+  const int maximum_rendered_frames = QThread::idealThreadCount();
+  auto frame_iterator = frame_render_order.cbegin();
+
+  for (int i=0; i<maximum_rendered_frames && frame_iterator!=frame_render_order.cend(); i++, frame_iterator++) {
+    StartTicket(frame_iterator->second, &watcher_thread, manager, frame_iterator->first,
+                mode, cache, force_size, force_matrix, force_format, force_color_output);
+  }
+
   finished_watcher_mutex_.lock();
 
   while (!IsCancelled()) {
@@ -165,6 +168,13 @@ bool RenderTask::Render(ColorManager* manager,
 
         emit ProgressChanged(progress_counter / total_length);
 
+        if (frame_iterator != frame_render_order.cend()) {
+          StartTicket(frame_iterator->second, &watcher_thread, manager, frame_iterator->first,
+                      mode, cache, force_size, force_matrix, force_format, force_color_output);
+
+          frame_iterator++;
+        }
+
       }
 
       delete watcher;
@@ -229,6 +239,24 @@ void RenderTask::IncrementRunningTickets()
   finished_watcher_mutex_.unlock();
 }
 
+void RenderTask::StartTicket(const QByteArray& hash, QThread* watcher_thread, ColorManager* manager,
+                             const rational& time, RenderMode::Mode mode, FrameHashCache* cache,
+                             const QSize &force_size, const QMatrix4x4 &force_matrix,
+                             VideoParams::Format force_format, ColorProcessorPtr force_color_output)
+{
+  RenderTicketWatcher* watcher = new RenderTicketWatcher();
+  watcher->setProperty("hash", hash);
+  PrepareWatcher(watcher, watcher_thread);
+
+  IncrementRunningTickets();
+
+  watcher->SetTicket(RenderManager::instance()->RenderFrame(viewer_, manager, time,
+                                                            mode, video_params_, audio_params_,
+                                                            force_size, force_matrix,
+                                                            force_format, force_color_output,
+                                                            cache));
+}
+
 void RenderTask::TicketDone(RenderTicketWatcher* watcher)
 {
   finished_watcher_mutex_.lock();

app/task/render/render.h

@@ -85,6 +85,8 @@ private:
 
   void IncrementRunningTickets();
 
+  void StartTicket(const QByteArray &hash, QThread *watcher_thread, ColorManager *manager, const rational &time, RenderMode::Mode mode, FrameHashCache *cache, const QSize &force_size, const QMatrix4x4 &force_matrix, VideoParams::Format force_format, ColorProcessorPtr force_color_output);
+
   Sequence* viewer_;
 
   VideoParams video_params_;