Portalocker is a library to provide an easy API to file locking.

An important detail to note is that on Linux and Unix systems the locks are
advisory by default. By specifying the -o mand option to the mount command it
is possible to enable mandatory file locking on Linux. This is generally not
recommended however. For more information about the subject:
  https://en.wikipedia.org/wiki/File_locking
  http://stackoverflow.com/questions/39292051/portalocker-does-not-seem-to-lock
  https://stackoverflow.com/questions/12062466/mandatory-file-lock-on-linux