From ee6d64773b3137ef59272517ee0491dd7748d46d Mon Sep 17 00:00:00 2001
From: Brett Cannon <bcannon@gmail.com>
Date: Sun, 22 Aug 2010 22:19:11 +0000
Subject: One of the joys of having test_multiprocessing occasionally execute
 after test_importlib is that it discovers special little race conditions. For
 instance, it turns out that importlib would throw an exception if two
 different Python processes both tried to create the __pycache__ directory as
 one process would succeed, causing the other process to fail as it didn't
 expect to get any "help". So now importlib simply stays calm and just accepts
 someone else did the work of creating the __pycache__ directory for it,
 moving on with life.

Closes issue #9572.
---
 Lib/importlib/_bootstrap.py | 44 ++++++++++++++++++++++++++------------------
 Misc/NEWS                   |  3 +++
 2 files changed, 29 insertions(+), 18 deletions(-)

diff --git a/Lib/importlib/_bootstrap.py b/Lib/importlib/_bootstrap.py
index 04d9bff..35b42ca 100644
--- a/Lib/importlib/_bootstrap.py
+++ b/Lib/importlib/_bootstrap.py
@@ -482,27 +482,35 @@ class _SourceFileLoader(_FileLoader, SourceLoader):
 
     def set_data(self, path, data):
         """Write bytes data to a file."""
+        parent, _, filename = path.rpartition(path_sep)
+        path_parts = []
+        # Figure out what directories are missing.
+        while parent and not _path_isdir(parent):
+            parent, _, part = parent.rpartition(path_sep)
+            path_parts.append(part)
+        # Create needed directories.
+        for part in reversed(path_parts):
+            parent = _path_join(parent, part)
+            try:
+                _os.mkdir(parent)
+            except IOError as exc:
+                # Probably another Python process already created the dir.
+                if exc.errno == errno.EEXIST:
+                    continue
+                # If can't get proper access, then just forget about writing
+                # the data.
+                elif errno == errno.EACCES:
+                    return
+                else:
+                    raise
         try:
-            with _closing(_io.FileIO(path, 'wb')) as file:
+            with _io.FileIO(path, 'wb') as file:
                 file.write(data)
         except IOError as exc:
-            if exc.errno == errno.ENOENT:
-                directory, _, filename = path.rpartition(path_sep)
-                sub_directories = []
-                while not _path_isdir(directory):
-                    directory, _, sub_dir = directory.rpartition(path_sep)
-                    sub_directories.append(sub_dir)
-                    for part in reversed(sub_directories):
-                        directory = _path_join(directory, part)
-                        try:
-                            _os.mkdir(directory)
-                        except IOError as exc:
-                            if exc.errno != errno.EACCES:
-                                raise
-                            else:
-                                return
-                return self.set_data(path, data)
-            elif exc.errno != errno.EACCES:
+            # Don't worry if you can't write bytecode.
+            if exc.errno == errno.EACCES:
+                return
+            else:
                 raise
 
 
diff --git a/Misc/NEWS b/Misc/NEWS
index ea3208c..f05f9ba 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -123,6 +123,9 @@ Extensions
 Library
 -------
 
+- Issue #9572: Importlib should not raise an exception if a directory it
+  thought it needed to create was done concurrently by another process.
+
 - Issue #9617: Signals received during a low-level write operation aren't
   ignored by the buffered IO layer anymore.
 
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