Improve performance of distributed_utils.broadcast_object
Improve performance of distributed_utils.broadcast_object

Summary:
Recommit D25291594 (https://github.com/pytorch/fairseq/commit/bb039fa2063dca1b388d6be2f64052b07fb556a2)

Original commit changeset: 64aead87ee84

Reviewed By: arendu

Differential Revision: D25518027

fbshipit-source-id: 5da303f835eb4b598728c7c7ef7c07538ea3b9b4

pytorch/fairseq,pytorch/fairseq,pytorch/fairseq