code: def parallel_backward(losses, sync=True):
      """Parallel Backward for CustomOp"""
  
      def _worker(loss):
          autograd.backward(loss)
  
      threads = [
          threading.Thread(target=_worker, args=(loss,))
          for loss in losses
      ]
      if sync:
          for thread in threads:
              thread.start()
          for thread in threads:
              thread.join()
      else:
          for loss in losses:
              loss.backward()
  
imports: import threading
  from mxnet import autograd
  from mxnet.gluon.utils import split_and_load
  from mxnet.ndarray import NDArray
label_desc: Use image node_id 5 for calling a global function with example usage: parallel_backward(losses, sync) without return types