Unlocks a file, allowing other processes to access the file.
The _unlock_file function unlocks the file specified by file. Unlocking a file allows access to the file by other processes. This function should not be called unless _lock_file was previously called on the file pointer. Calling _unlock_file on a file that isn't locked may result in a deadlock. For an example, see _lock_file.
For additional compatibility information, see Compatibility in the Introduction.