GpuChannelHost* RenderThreadImpl::GetGpuChannel() {
  if (!gpu_channel_.get())
    return NULL;

  if (gpu_channel_->IsLost())
    return NULL;

  return gpu_channel_.get();
}

The product contains a concurrent code sequence that requires temporary, exclusive access to a shared resource, but a timing window exists in which the shared resource can be modified by another code sequence operating concurrently.