Very small race condition in file field saving

[Malcolm Tredinnick]

Noticed this whilst reading Model._save_FIELD_file() for another reason. The directory name used to save the file can be sensitive to the current datetime value, since upload_to directories can contain format strings. This directory name is computed a couple of times in this function, from what I can work out: once when creating the directories at the top of the function and once when call field.get_filename().

It's possible that the time delay between creating the directory and using the directory lower down could be sufficiently long that the name actually changes. For example, using day-based formats and then clock crosses midnight. The directory name should be the same throughout the code.

[scum]

Added a optional parameter to get_filename fixingthe race condition. Not as pretty, but the only way I can think to do it right.

[Koen Biermans]

This part of the code was changed drastically in the file storage refactor. I can not find a similar race condition in the current FileField implementation.

Closing as fixed.