[GitHub] [buildstream] gtristan commented on a diff in pull request #1832: Fix downloadablefile race condition

["gtristan (via GitHub)" <gi...@apache.org>]

gtristan commented on code in PR #1832:
URL: https://github.com/apache/buildstream/pull/1832#discussion_r1318095064


##########
src/buildstream/downloadablefilesource.py:
##########
@@ -235,8 +235,12 @@ def _ensure_mirror(self, activity_name: str):
                 return self.ref
 
             # Make sure url-specific mirror dir exists.
-            if not os.path.isdir(self._mirror_dir):
-                os.makedirs(self._mirror_dir)
+            try:
+                os.makedirs(self._mirror_dir, exist_ok=True)

Review Comment:
   This can happen whenever you have 2 separate elements which download the same downloadable file source.
   
   The later call to `os.rename()` below guarantees the required atomicity, but the call to `os.makedirs()` will collide in the case that both sources try to create the directory after both having passed the `not os.path.isdir(self._mirror_dir)` check.
   



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