The lockfile module exports a FileLock class which provides a simple API for
locking files. Unlike the Windows msvcrt.locking function, the Unix
fcntl.flock, fcntl.lockf and the deprecated posixfile module, the API is
identical across both Unix (including Linux and Mac) and Windows platforms. The
lock mechanism relies on the atomic nature of the link (on Unix) and mkdir (on
Windows) system calls.
