The lockfile API is a handy way to obtain a file that is cleaned
up if you die(). But sometimes you would need this sequence to
work:
1. hold_lock_file_for_update() to get a file descriptor for
writing;
2. write the contents out, without being able to decide if the
results should be committed or rolled back;
3. do something else that makes the decision --- and this
"something else" needs the lockfile not to have an open file
descriptor for writing (e.g. Windows do not want a open file
to be renamed);
4. call commit_lock_file() or rollback_lock_file() as
appropriately.
This adds close_lock_file() you can call between step 2 and 3 in
the above sequence.