#272 Fix race condition in DirectoryStore (#318)

* #272 fix race condition to make folders in directory store

* #272 remove FileNotFoundError for python 2 support

* Change OSError to KeyError to make tests pass

* Only catch `OSError` if its `errno` equal `EEXIST`

On Python 3, we would only want to catch the race case here by checking
for the `FileExistsError` and suppressing raising for that case. However
there is no `FileExistsError` on Python 2. Only `OSError` exists on
Python 2/3. However that catches some other errors that we might not
want to suppress here. So we check the `errno` of the `OSError` instance
to verify it is caused by an existing file/directory represented by the
`EEXIST` error number. This amounts to catching the `FileExistsError` in
a Python 2/3 friendly way. All other `OSErrors` we raise as before.

* Drop generic `Exception` case in `DirectoryStore`

As we now properly handle the existing file case properly, go ahead and
drop the generic exception case. This should now raise some errors that
were hidden previously.

Author: jmswaney

zarr/storage.py

@@ -23,6 +23,7 @@
 import zipfile
 import shutil
 import atexit
+import errno
 import re
 import sys
 import json
@@ -745,8 +746,9 @@ def __setitem__(self, key, value):
         if not os.path.exists(dir_path):
             try:
                 os.makedirs(dir_path)
-            except Exception:
-                raise KeyError(key)
+            except OSError as e:
+                if e.errno != errno.EEXIST:
+                    raise KeyError(key)
 
         # write to temporary file
         temp_path = None

zarr/tests/data/store.zip

@@ -0,0 +1 @@
+bar