lib/mongoid/locker/wrapper.rb
require 'mongoid/compatibility'
if Mongoid::Compatibility::Version.mongoid5?
require 'mongoid/locker/wrapper5'
elsif Mongoid::Compatibility::Version.mongoid4?
require 'mongoid/locker/wrapper4'
elsif Mongoid::Compatibility::Version.mongoid3?
require 'mongoid/locker/wrapper3'
elsif Mongoid::Compatibility::Version.mongoid2?
require 'mongoid/locker/wrapper2'
else
fail 'incompatible Mongoid version'
end