fix #108

[lanpa]

Root cause: python's multiprocessing object was not released properly.

[codecov-io]

Codecov Report

Merging #560 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #560      +/-   ##
==========================================
+ Coverage   87.81%   87.82%   +<.01%     
==========================================
  Files          39       39              
  Lines        2815     2817       +2     
==========================================
+ Hits         2472     2474       +2     
  Misses        343      343

Impacted Files	Coverage Δ
tensorboardX/event_file_writer.py	95.28% <100%> (+0.09%)	⬆️

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