class_docstr: Snapshot writer that uses a separate thread.
  
  This class creates a new thread that invokes the actual saving function.
  
  .. seealso::
  
      - :meth:`chainer.training.extensions.snapshot`
code: def __init__(self, savefun=npz.save_npz, **kwds):
      super(ThreadWriter, self).__init__(savefun=savefun, **kwds)
  
imports: import multiprocessing
  import os
  import shutil
  import threading
  from six.moves import queue
  from chainer.serializers import npz
  from chainer import utils
label_desc: Use image node_id 1 to create a new ThreadWriter object from inherited base classes: StandardWriter with example: obj = ThreadWriter(savefun)