Deleting a possibly locked file in c

Question

I am using fcntl locks in C on linux and have a dilemma of trying to delete a file that may possibly be locked from other processes that also check for the fcntl locking mechanism. What would be the preferred way of handling this file which must be deleted, (Should I simply delete the file w/o regard of other processes that may have reader locks or is there a better way)? Any help would be much appreciated.

Answer 1

On UNIX systems, it is possible to unlink a file while it is still open; doing so decrements the reference count on the file, but the actual file and its inode remains around until the reference count goes to zero.

Answer 2

Moreover, locks on UNIX system are advisory by default, not mandatory, so that locking a file does not prevent it from being open or unlinked, just from being locked again.

Answer 3

As others have noted, you are free to delete the file even while you hold the lock.

Now, a cautionary note: you didn't mention why processes are locking this file, but you should be aware that if you are using that file for interprocess synchronization, deleting it is a good way to introduce subtle race conditions into your system, basically because there's no way to atomically create AND lock the file in a single operation.

For example, process AA might create the file, with the intention of locking it immediately to do whatever updates it needs to do. However, there's nothing to prevent process BB from grabbing the lock on the file first, then deleting the file, leaving process AA with a handle to the now deleted file. Process AA will still be able to lock and update that file, but those updates will effectively be "lost" because the file's already been deleted.