A Philosophy of Software Design

by John Ousterhout

File deletion provides another example of how errors can be defined away. The Windows operating system does not permit a file to be deleted if it is open in a process. This is a continual source of frustration for developers and users. In order to delete a file that is in use, the user must search through the system to find the process that has the file open, and then kill that process. Sometimes users give up and reboot their system, just so they can delete a file. The Unix operating system defines file deletion more elegantly. In Unix, if a file is open when it is deleted, Unix does not delete the file immediately. Instead, it marks the file for deletion, then the delete operation returns successfully. The file name has been removed from its directory, so no other processes can open the old file and a new file with the same name can be created, but the existing file data persists. Processes that already have the file open can continue to read it and write it normally. Once the file has been closed by all of the accessing processes, its data is freed. The Unix approach defines away two different kinds of errors. First, the delete operation no longer returns an error if the file is currently in use; the delete succeeds, and the file will eventually be deleted. Second, deleting a file that’s in use does not create exceptions for the processes using the file. One possible approach to this problem would have been to delete the file immediately and mark all of the opens of the...

Unix vs Windows file exceptions