Shell::~Shell() {
  PersistentCache::GetCacheForProcess()->RemoveWorkerTaskRunner(
      task_runners_.GetIOTaskRunner());

  if (auto vm = blink::DartVM::ForProcessIfInitialized()) {
    vm->GetServiceProtocol().RemoveHandler(this);
  }

  fml::AutoResetWaitableEvent ui_latch, gpu_latch, platform_latch, io_latch;

  fml::TaskRunner::RunNowOrPostTask(
      task_runners_.GetUITaskRunner(),
      fml::MakeCopyable([engine = std::move(engine_), &ui_latch]() mutable {
        engine.reset();
        ui_latch.Signal();
      }));
  ui_latch.Wait();

  fml::TaskRunner::RunNowOrPostTask(
      task_runners_.GetGPUTaskRunner(),
      fml::MakeCopyable(
          [rasterizer = std::move(rasterizer_), &gpu_latch]() mutable {
            rasterizer.reset();
            gpu_latch.Signal();
          }));
  gpu_latch.Wait();

  fml::TaskRunner::RunNowOrPostTask(
      task_runners_.GetIOTaskRunner(),
      fml::MakeCopyable([io_manager = std::move(io_manager_),
                         platform_view = platform_view_.get(),
                         &io_latch]() mutable {
        io_manager.reset();
        if (platform_view) {
          platform_view->ReleaseResourceContext();
        }
        io_latch.Signal();
      }));

  io_latch.Wait();

  // The platform view must go last because it may be holding onto platform side
  // counterparts to resources owned by subsystems running on other threads. For
  // example, the NSOpenGLContext on the Mac.
  fml::TaskRunner::RunNowOrPostTask(
      task_runners_.GetPlatformTaskRunner(),
      fml::MakeCopyable([platform_view = std::move(platform_view_),
                         &platform_latch]() mutable {
        platform_view.reset();
        platform_latch.Signal();
      }));
  platform_latch.Wait();
}

void SkiaUnrefQueue::Unref(SkRefCnt* object) {
  std::lock_guard<std::mutex> lock(mutex_);
  objects_.push_back(object);
  if (!drain_pending_) {
    drain_pending_ = true;
    task_runner_->PostDelayedTask(
        [strong = fml::Ref(this)]() { strong->Drain(); }, drain_delay_);
  }
}

void SkiaUnrefQueue::Drain() {
  std::deque<SkRefCnt*> skia_objects;
  {
    std::lock_guard<std::mutex> lock(mutex_);
    objects_.swap(skia_objects);
    drain_pending_ = false;
  }

  for (SkRefCnt* skia_object : skia_objects) {
    skia_object->unref();
  }
}