Sometimes some gem might enable JRuby.objectspace (see example rubyzip/rubyzip#252) and it is hard to notice when some of your dependencies in your appication is doing that.

As JRuby.objectspace is not meant to be used in production then it would be good to print a warning to stderr when it is enabled - it will both discourage its usage as well as you can more easily notice when some of your dependencies has enabled it.