Fix race condition in _bypass_ensure_directory

This fixes a race condition in _bypass_ensure_directory where
two threads or processes may erroneously fail because they are
both creating the same directory. A more robust implementation
of this may involve exposing the un-wrapped os.makedirs.

Originally reported with proposed patch by @JonKohler in
github PR #1412. This patch came out of discussions on that
thread.

1 files changed, 9 insertions, 1 deletions

diff --git a/pkg_resources/__init__.py b/pkg_resources/__init__.py
index 67015408..4f42156d 100644
--- a/pkg_resources/__init__.py
+++ b/pkg_resources/__init__.py
@@ -47,6 +47,11 @@ except ImportError:
     # Python 3.2 compatibility
     import imp as _imp
 
+try:
+    FileExistsError
+except NameError:
+    FileExistsError = OSError
+
 from pkg_resources.extern import six
 from pkg_resources.extern.six.moves import urllib, map, filter
 
@@ -3030,7 +3035,10 @@ def _bypass_ensure_directory(path):
     dirname, filename = split(path)
     if dirname and filename and not isdir(dirname):
         _bypass_ensure_directory(dirname)
-        mkdir(dirname, 0o755)
+        try:
+            mkdir(dirname, 0o755)
+        except FileExistsError:
+            pass
 
 
 def split_sections(s):