Re: Writing to a file atomically without renaming

[waswas-fng]

If this is on unix you can change the group of the file and its parent dir to a group that is common between both user1 and user2. If you also chmod 770 and g+s (group sicky bit) the parent dir, you should be in a situation where any file created is set to the group of the parent dir. This allows you to read and write to the file as power from both user1 and user2.