Suppress leaked semaphore warnings

Summary: Pull Request resolved: https://github.com/fairinternal/fairseq-py/pull/844

Differential Revision: D16985131

Pulled By: myleott

fbshipit-source-id: 66ba3b9aa0cdf329a1e38fc09786f34906afdb43

fairseq/data/iterators.py

@@ -5,6 +5,7 @@
 
 import itertools
 import math
+import os
 
 import numpy as np
 import torch
@@ -248,6 +249,9 @@ class EpochBatchIterator(EpochBatchIterating):
         if offset > 0 and offset >= len(batches):
             return None
 
+        if self.num_workers > 0:
+            os.environ['PYTHONWARNINGS'] = 'ignore:semaphore_tracker:UserWarning'
+
         return CountingIterator(
             torch.utils.data.DataLoader(
                 self.dataset,