No guards against cache corruption via multiple clients uploading the same file at the same time.

[markstos]

From looking at the code, it seems nothing prevents two jobs from attempting to upload the same file in parallel. It appears this could result in a corrupted file.

We have recently experienced a couple cases of file corruption of our cache managed by this server. While we have not pinpointed the cause and don't have an exact reproduction, it looks like nothing in the code guards against this.