When you use rename to overwrite a file, it guarentees that at any point in time, newpath will refer to either the original file, or the new file. This is atomi

When you use rename to overwrite a file, it guarentees that at any point in time, newpath will refer to either the original file, or the new file. This is atomic enough to give you effectivly atomic file creation with contents. It is not technically atomic, because there is a period where oldpath and newpath both refer to the same file, but I don't think that is an issue for this usecase.