Handle multiple processes trying to create the data home directory

python/paddle/v2/dataset/common.py

@@ -27,10 +27,14 @@ __all__ = ['DATA_HOME', 'download', 'md5file', 'split', 'cluster_files_reader']
 
 DATA_HOME = os.path.expanduser('~/.cache/paddle/dataset')
 
-if not os.path.exists(DATA_HOME):
-    try:
+# When running unit tests, there could be multiple processes that
+# trying to create DATA_HOME directory simultaneously, so we cannot
+# use a if condition to check for the existence of the directory;
+# instead, we use the filesystem as the synchronization mechanism by
+# catching returned errors.
+try:
     os.makedirs(DATA_HOME)
-    except OSError as exc:
+except OSError as exc:
     if exc.errno != errno.EEXIST:
         raise
     pass