FilePath.createDirectoryIdempotent()

	@zooko reported
Trac ID	trac#5280
Type	enhancement
Created	2011-09-28 06:55:41Z

In the Tahoe-LAFS project we sometimes want to create a directory if it isn't already there, and we don't want to get an exception if there is a race condition so that the directory get created by some other process at the same moment our process is trying to create it. Therefore we use this utility function fileutil.make_dirs.

Here is a patch which adds FilePath.createDirectoryIdempotent and FilePath.makedirsIdempotent. The implementation in this patch is superior to the one in fileutil.make_dirs because this one will correctly propagate an exception (for example, Permission Denied or some random exception due to your disk dying) even if there is a directory existing at that point.

This patch includes detailed tests which I hope sufficiently illustrate why the implementations of these two methods are the way they are.

This patch is based on top of the patch already posted to [#5279](https://github.com/twisted/twisted/issues/5279). If #5279 is not already reviewed then you'll need to review it as well to review this.

Thank you!

Attachments:

• createDirectoryIdempotent.diff (11031 bytes) - added by zooko on 2011-09-28 06:55:54Z -

trac-id__5280 5280
type__enhancement enhancement
reporter__zooko zooko
priority__normal normal
milestone__ 
branch__ 
branch_author__ 
status__new new
resolution__None None
component__core core
keywords__ 
time__1317192941000000 1317192941000000
changetime__1317408891000000 1317408891000000
version__None None
owner__zooko zooko
cc__zooko

Review the attached createDirectoryIdempotent.diff and issue #5279 first, then inspect allmydata/util/fileutil.py and the FilePath methods it extends. Confirm that the detailed tests cover concurrent directory creation and that exceptions such as permission errors still propagate; done means the proposed methods and tests are integrated.