Interpreter Internals

This chapter lists several modules that allow to introspect and hack the Ruby interpreter at execution time.


The ObjectSpace module contains a number of routines that interact with the garbage collection facility and allow you to traverse all living objects with an iterator.

ObjectSpace also provides support for object finalizers, procs that will be called when a specific object is about to be destroyed by garbage collection.

require 'objspace'

a = "A"
b = "B"

ObjectSpace.define_finalizer(a, proc {|id| puts "Finalizer one on #{id}" })
ObjectSpace.define_finalizer(b, proc {|id| puts "Finalizer two on #{id}" })


Finalizer two on 537763470
Finalizer one on 537763480

ObjectSpace Reference

objspace standard library

Standard library objspace provides some extensions for ObjectSpace module.

The objspace library extends the ObjectSpace module and adds several methods to get internal statistic information about object/memory management.

You need to require objspace’` to use this extension module.

Generally, you SHOULD NOT use this library if you do not know about the MRI implementation. Mainly, this library is for (memory) profiler developers and MRI developers who need to know about MRI memory usage.

ObjectSpace Reference


The GC module provides an interface to Ruby’s mark and sweep garbage collection mechanism.

Some of the underlying methods are also available via the ObjectSpace module.

You may obtain information about the operation of the GC through GC::Profiler.

GC Reference


A class that provides the functionality of Kernel#set_trace_func in a nice Object-Oriented API.


We can use TracePoint to gather information specifically for exceptions:

trace = do |tp|
    p [tp.lineno, tp.event, tp.raised_exception]
#=> #<TracePoint:disabled>

#=> false

0 / 0
#=> [5, :raise, #<ZeroDivisionError: divided by 0>]


If you don’t specify the type of events you want to listen for, TracePoint will include all available events.

Note do not depend on current event set, as this list is subject to change. Instead, it is recommended you specify the type of events you want to use.

To filter what is traced, you can pass any of the following as events:

  • :line: execute code on a new line
  • :class: start a class or module definition
  • :end: finish a class or module definition
  • :call: call a Ruby method
  • :return: return from a Ruby method
  • :c_call: call a C-language routine
  • :c_return: return from a C-language routine
  • :raise: raise an exception
  • :b_call: event hook at block entry
  • :b_return: event hook at block ending
  • :thread_begin: event hook at thread beginning
  • :thread_end: event hook at thread ending
  • :fiber_switch: event hook at fiber switch
  • :script_compiled: new Ruby code compiled (with eval, load or require)

TracePoint Reference