Since the SystemTimer gem is admittedly a hack (though a very useful and appreciated hack) to work around implementation issues for a limited subset of ruby implementations (ie: 1.8.x), it would be great if the gem could detect the current environment in which is it is running and only take effect when appropriate. This would would allow otherwise compatible gems to run successfully in other environments (ie: Ruby 1.9, jruby, etc..).
see also #10
If you use a Gemfile, you can target a dependency for ruby 1.8 only like that:
gem 'SystemTimer', :platforms => :mri_18
apparently, the 'official' solution is to create a different gem version for each platform.