Don't leak threads on exit (#21438)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/21438
ghimport-source-id: 33f145f5b3508163365442c22a223c4a44e677d8
Differential Revision: D15738856
fbshipit-source-id: 656e8d0e3d0d22f116e3ab66bf0282608d6f1a76
