I need a library that provides both shared and exclusive locks on files.

oslo.concurrency and lockfile attempt the highest common factor approach
based on atomic file creation, which only provides exclusive locks

portalocker is more portable and provides shared and exclusive locks,
but doesn't work with directories since it requires a file object,
and python2 doesn't let you have a file object for a directory.

Also its timeout approach is to non-blocking flock in a loop until the
timeout period is over,
which is less performant than a proper blocking lock with wakeup.