object_walker.rb

# object_walker.rb
require 'java'
require 'jruby/util'

module ObjectWalker
  import com.sun.jdi.Bootstrap
  
  # Generate a histogram of all classes in the system
  def self.histogram
    classes = VM.all_classes
    counts = VM.instance_counts(classes)
    classes.zip(counts)
  end
      
  # Initialize the singleton VirtualMachine reference
  def self.init_vm
    raise "Already initialize" if defined? VM
    vmm = Bootstrap.virtual_machine_manager
    sock_conn = vmm.attaching_connectors[0] # not guaranteed to be Socket
    args = sock_conn.default_arguments
    args['port'].value = "12345"
    vm = sock_conn.attach(args)
  end
  
  VM ||= init_vm
end

object_walker_test.rb

require 'object_walker'

histo = ObjectWalker.histogram
histo.sort! {|a,b| b[1] <=> a[1]}
histo.each do |cls,num|
  if num == 0 || cls.name[0..4] != 'ruby.' || cls.name[5..7] == 'jit'
    next
  end
  puts "#{num} instances of #{cls}"
end

session

~/projects/jruby ➔ jruby object_walker_test.rb
11685 instances of class ruby.TZInfo.TimezoneTransitionInfo (loaded by instance of org.jruby.util.ClassCache$OneShotClassLoader(id=5790))
1040 instances of class ruby.Gem.Version (loaded by instance of org.jruby.util.ClassCache$OneShotClassLoader(id=5791))
1007 instances of class ruby.Gem.Version (loaded by instance of org.jruby.util.ClassCache$OneShotClassLoader(id=5792))
984 instances of class ruby.Gem.Requirement (loaded by instance of org.jruby.util.ClassCache$OneShotClassLoader(id=5793))
951 instances of class ruby.Gem.Requirement (loaded by instance of org.jruby.util.ClassCache$OneShotClassLoader(id=5794))
592 instances of class ruby.TZInfo.TimezoneOffsetInfo (loaded by instance of org.jruby.util.ClassCache$OneShotClassLoader(id=5795))
428 instances of class ruby.Gem.Dependency (loaded by instance of org.jruby.util.ClassCache$OneShotClassLoader(id=5796))
411 instances of class ruby.Gem.Dependency (loaded by instance of org.jruby.util.ClassCache$OneShotClassLoader(id=5797))
277 instances of class ruby.Gem.Specification (loaded by instance of org.jruby.util.ClassCache$OneShotClassLoader(id=5798))
269 instances of class ruby.Gem.Specification (loaded by instance of org.jruby.util.ClassCache$OneShotClassLoader(id=5799))
142 instances of class ruby.ActiveSupport.TimeZone (loaded by instance of org.jruby.util.ClassCache$OneShotClassLoader(id=5800))
118 instances of class ruby.TZInfo.DataTimezoneInfo (loaded by instance of org.jruby.util.ClassCache$OneShotClassLoader(id=5801))
118 instances of class ruby.TZInfo.DataTimezone (loaded by instance of org.jruby.util.ClassCache$OneShotClassLoader(id=5802))
41 instances of class ruby.Gem.Platform (loaded by instance of org.jruby.util.ClassCache$OneShotClassLoader(id=5803))
41 instances of class ruby.Gem.Platform (loaded by instance of org.jruby.util.ClassCache$OneShotClassLoader(id=5804))
14 instances of class ruby.Mime.Type (loaded by instance of org.jruby.util.ClassCache$OneShotClassLoader(id=5805))
12 instances of class ruby.Set (loaded by instance of org.jruby.util.ClassCache$OneShotClassLoader(id=5806))
8 instances of class ruby.ActionController.MiddlewareStack.Middleware (loaded by instance of org.jruby.util.ClassCache$OneShotClassLoader(id=5807))
8 instances of class ruby.ActionView.Template (loaded by instance of org.jruby.util.ClassCache$OneShotClassLoader(id=5808))
7 instances of class ruby.ActionController.Routing.DividerSegment (loaded by instance of org.jruby.util.ClassCache$OneShotClassLoader(id=5809))
6 instances of class ruby.TZInfo.LinkedTimezone (loaded by instance of org.jruby.util.ClassCache$OneShotClassLoader(id=5802))
6 instances of class ruby.TZInfo.LinkedTimezoneInfo (loaded by instance of org.jruby.util.ClassCache$OneShotClassLoader(id=5801))
4 instances of class ruby.ActionController.Routing.DynamicSegment (loaded by instance of org.jruby.util.ClassCache$OneShotClassLoader(id=5809))
2 instances of class ruby.Gem.SourceIndex (loaded by instance of org.jruby.util.ClassCache$OneShotClassLoader(id=5810))
2 instances of class ruby.ActiveSupport.Deprecation.DeprecatedConstantProxy (loaded by instance of org.jruby.util.ClassCache$OneShotClassLoader(id=5811))
2 instances of class ruby.ActiveSupport.Callbacks.Callback (loaded by instance of org.jruby.util.ClassCache$OneShotClassLoader(id=5812))
2 instances of class ruby.ActionView.Template.EagerPath (loaded by instance of org.jruby.util.ClassCache$OneShotClassLoader(id=5813))
2 instances of class ruby.ActionController.Routing.Route (loaded by instance of org.jruby.util.ClassCache$OneShotClassLoader(id=5814))
2 instances of class ruby.ActionController.Routing.ControllerSegment (loaded by instance of org.jruby.util.ClassCache$OneShotClassLoader(id=5809))
2 instances of class ruby.OptionParser.Switch.NoArgument (loaded by instance of org.jruby.util.ClassCache$OneShotClassLoader(id=5815))
2 instances of class ruby.OptionParser.Switch.NoArgument (loaded by instance of org.jruby.util.ClassCache$OneShotClassLoader(id=5816))
1 instances of class ruby.ActionController.Dispatcher (loaded by instance of org.jruby.util.ClassCache$OneShotClassLoader(id=5817))
1 instances of class ruby.ActionController.Failsafe (loaded by instance of org.jruby.util.ClassCache$OneShotClassLoader(id=5818))
1 instances of class ruby.ActionController.Filters.BeforeFilter (loaded by instance of org.jruby.util.ClassCache$OneShotClassLoader(id=5812))
1 instances of class ruby.ActionController.ParamsParser (loaded by instance of org.jruby.util.ClassCache$OneShotClassLoader(id=5819))
1 instances of class ruby.ActionController.Routing.OptionalFormatSegment (loaded by instance of org.jruby.util.ClassCache$OneShotClassLoader(id=5809))
1 instances of class ruby.ActionController.Routing.RouteBuilder (loaded by instance of org.jruby.util.ClassCache$OneShotClassLoader(id=5820))
1 instances of class ruby.ActionController.Routing.RouteSet (loaded by instance of org.jruby.util.ClassCache$OneShotClassLoader(id=5821))
1 instances of class ruby.ActionController.Routing.RouteSet.NamedRouteCollection (loaded by instance of org.jruby.util.ClassCache$OneShotClassLoader(id=5822))
1 instances of class ruby.ActionController.Session.CookieStore (loaded by instance of org.jruby.util.ClassCache$OneShotClassLoader(id=5823))
1 instances of class ruby.ActionController.StringCoercion (loaded by instance of org.jruby.util.ClassCache$OneShotClassLoader(id=5824))
1 instances of class ruby.ActiveSupport.BufferedLogger (loaded by instance of org.jruby.util.ClassCache$OneShotClassLoader(id=5825))
1 instances of class ruby.ActiveSupport.Cache.MemoryStore (loaded by instance of org.jruby.util.ClassCache$OneShotClassLoader(id=5826))
1 instances of class ruby.ActiveSupport.Inflector.Inflections (loaded by instance of org.jruby.util.ClassCache$OneShotClassLoader(id=5827))
1 instances of class ruby.ActiveSupport.MessageVerifier (loaded by instance of org.jruby.util.ClassCache$OneShotClassLoader(id=5828))
1 instances of class ruby.ActiveSupport.Multibyte.Codepoint (loaded by instance of org.jruby.util.ClassCache$OneShotClassLoader(id=5829))
1 instances of class ruby.ActiveSupport.Multibyte.UnicodeDatabase (loaded by instance of org.jruby.util.ClassCache$OneShotClassLoader(id=5830))
1 instances of class ruby.ERB (loaded by instance of org.jruby.util.ClassCache$OneShotClassLoader(id=5831))
1 instances of class ruby.Gem.CommandManager (loaded by instance of org.jruby.util.ClassCache$OneShotClassLoader(id=5832))
1 instances of class ruby.Gem.CommandManager (loaded by instance of org.jruby.util.ClassCache$OneShotClassLoader(id=5833))
1 instances of class ruby.Gem.ConfigFile (loaded by instance of org.jruby.util.ClassCache$OneShotClassLoader(id=5834))
1 instances of class ruby.Gem.ConfigFile (loaded by instance of org.jruby.util.ClassCache$OneShotClassLoader(id=5835))
1 instances of class ruby.Gem.GemPathSearcher (loaded by instance of org.jruby.util.ClassCache$OneShotClassLoader(id=5836))
1 instances of class ruby.Gem.GemPathSearcher (loaded by instance of org.jruby.util.ClassCache$OneShotClassLoader(id=5837))
1 instances of class ruby.Gem.SourceIndex (loaded by instance of org.jruby.util.ClassCache$OneShotClassLoader(id=5838))
1 instances of class ruby.I18n.Backend.Simple (loaded by instance of org.jruby.util.ClassCache$OneShotClassLoader(id=5839))
1 instances of class ruby.I18n.Config (loaded by instance of org.jruby.util.ClassCache$OneShotClassLoader(id=5840))
1 instances of class ruby.JRuby.Rack.Booter (loaded by instance of org.jruby.util.ClassCache$OneShotClassLoader(id=5841))
1 instances of class ruby.JRuby.Rack.Errors (loaded by instance of org.jruby.util.ClassCache$OneShotClassLoader(id=5842))
1 instances of class ruby.JRuby.Rack.RailsBooter (loaded by instance of org.jruby.util.ClassCache$OneShotClassLoader(id=5843))
1 instances of class ruby.JRuby.Rack.RailsRequestSetup (loaded by instance of org.jruby.util.ClassCache$OneShotClassLoader(id=5844))
1 instances of class ruby.JRuby.Rack.RailsWebInfLayout (loaded by instance of org.jruby.util.ClassCache$OneShotClassLoader(id=5845))
1 instances of class ruby.JRuby.Rack.ServletLog (loaded by instance of org.jruby.util.ClassCache$OneShotClassLoader(id=5846))
1 instances of class ruby.JRuby.Rack.WebInfLayout (loaded by instance of org.jruby.util.ClassCache$OneShotClassLoader(id=5847))
1 instances of class ruby.OptionParser.List (loaded by instance of org.jruby.util.ClassCache$OneShotClassLoader(id=5848))
1 instances of class ruby.OptionParser.List (loaded by instance of org.jruby.util.ClassCache$OneShotClassLoader(id=5849))
1 instances of class ruby.Rack.Adapter.Rails (loaded by instance of org.jruby.util.ClassCache$OneShotClassLoader(id=5850))
1 instances of class ruby.Rack.Builder (loaded by instance of org.jruby.util.ClassCache$OneShotClassLoader(id=5851))
1 instances of class ruby.Rack.File (loaded by instance of org.jruby.util.ClassCache$OneShotClassLoader(id=5852))
1 instances of class ruby.Rack.File (loaded by instance of org.jruby.util.ClassCache$OneShotClassLoader(id=5853))
1 instances of class ruby.Rack.Handler.Servlet (loaded by instance of org.jruby.util.ClassCache$OneShotClassLoader(id=5854))
1 instances of class ruby.Rack.Handler.Servlet (loaded by instance of org.jruby.util.ClassCache$OneShotClassLoader(id=5855))
1 instances of class ruby.Rack.Head (loaded by instance of org.jruby.util.ClassCache$OneShotClassLoader(id=5856))
1 instances of class ruby.Rack.MethodOverride (loaded by instance of org.jruby.util.ClassCache$OneShotClassLoader(id=5857))
1 instances of class ruby.Rack.ShowStatus (loaded by instance of org.jruby.util.ClassCache$OneShotClassLoader(id=5858))
1 instances of class ruby.Rails.Configuration (loaded by instance of org.jruby.util.ClassCache$OneShotClassLoader(id=5859))
1 instances of class ruby.Rails.VendorGemSourceIndex (loaded by instance of org.jruby.util.ClassCache$OneShotClassLoader(id=5860))
1 instances of class ruby.Set (loaded by instance of org.jruby.util.ClassCache$OneShotClassLoader(id=5861))
1 instances of class ruby.Trinidad.RailsWebApp (loaded by instance of org.jruby.util.ClassCache$OneShotClassLoader(id=5862))
1 instances of class ruby.Trinidad.Server (loaded by instance of org.jruby.util.ClassCache$OneShotClassLoader(id=5863))