Dispelling the Dark Magic: Inside a Ruby Debugger

Presentation by Daniel Azuma at RubyConf 2017. Covers how to implement a basic debugger for Ruby programs, and discusses some techniques behind the Stackdriver Debugger for Ruby. See also the live coding artifact at https://github.com/dazuma/google-snippets/blob/master/mini-debug

Transcript

1. Dispelling the dark magic: inside a Ruby debugger Daniel Azuma November 16, 2017
2. photo by Daniel Azuma
3. https://eclipse2017.nasa.gov/eclipse-who-what-where-when-and-how
4. https://tenderlovemaking.com/2016/02/05/i-am-a-puts-debuggerer.html
5. Live coding!? OMG!!
6. Live coding!? OMG!!
7. Daniel Azuma http:/ /daniel-azuma.com/
9. Lawyercat says: Code samples are: Copyright 2017 Google Inc. Licensed under the Apache License, Version 2.0 (the "License"); you may not use this code except in compliance with the License. You may obtain a copy of the License at: https://www.apache.org/licenses/LICENSE-2.0 Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.
10. Breakpoints by file/line Command shell Step in/out/over Debugger features
11. ( Live coding session )
12. TracePoint
13. TracePoint.trace :call do |tp| puts "Called method #{tp.method_id}" end
14. line class end call return c_call c_return raise b_call b_return thread_begin thread_end fiber_switch TracePoint event types
15. line class end call return c_call c_return raise b_call b_return thread_begin thread_end fiber_switch TracePoint event types
16. ( Live coding session )
17. Inception (2010) © Warner Bros. https://commons.wikimedia.org/wiki/File:Solar_eclipse_1878Jul29-Corona_Pikes_peak_Langley.png
18. Stackdriver Debugger
19. https://commons.wikimedia.org/wiki/File:Lunar_eclipse_al-Biruni.jpg Threads
20. TracePoint.trace :call do |tp| puts "Called method #{tp.method_id}" end
21. void rb_thread_add_event_hook(VALUE thval, rb_event_hook_func_t func, rb_event_flag_t events, VALUE data); int rb_thread_remove_event_hook(VALUE thval, rb_event_hook_func_t func);
22. Ruby interface to thread-scoped TracePoint call?
23. https://commons.wikimedia.org/wiki/File:Astronomy;_a_view_of_London_in_1748,_with_diagrams_of_an_ecl_Wellcome_V0024734.jpg Speed
24. file_events = [:call, :b_call, :return, :b_return, :fiber_switch] TracePoint.trace *file_events do |tp| if @breakpoint_files.include? tp.path @line_trace.enable else @line_trace.disable end end
26. Native breakpoint API?
27. https://commons.wikimedia.org/wiki/File:Macrobius,_lunar_and_solar_eclipse.jpg Side effects
28. Object state changes External side effects Side effects
29. BYTE_CODE_BLACKLIST = %w( setinstancevariable setclassvariable setconstant setglobal defineclass opt_ltlt opt_aset opt_aset_with ).freeze
30. C_METHOD_WHITELIST = %w( Array#+ Array#- Array#== Array#any? Array#assoc Array#at Array#bsearch # etc...
32. Immutability?
33. Immutability? Code jails?
34. Immutability? Code jails? Guilds??
36. Debuggers (the basics) are straightforward!
37. Ruby has partial support for debuggers
38. Try out a debugger! Byebug: interactive debugger shell https://github.com/deivid-rodriguez/byebug Stackdriver debugger: for live web applications https://cloud.google.com/debugger https://github.com/GoogleCloudPlatform/google-cloud-ruby/tree/ master/google-cloud-debugger
39. It's just Ruby
40. Thanks for viewing! Daniel Azuma dazuma@gmail.com @danielazuma