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
   

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2. photo by Daniel Azuma
   

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3. https://eclipse2017.nasa.gov/eclipse-who-what-where-when-and-how
   

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4. https://tenderlovemaking.com/2016/02/05/i-am-a-puts-debuggerer.html
   

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5. Live coding!? OMG!!
   
   

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6. Live coding!? OMG!!
   
   

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7. Daniel Azuma
   http:/
   /daniel-azuma.com/
   

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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.
   

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10. Breakpoints by file/line
    Command shell
    Step in/out/over
    Debugger features
    

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11. ( Live coding session )
    

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12. TracePoint
    

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13. TracePoint.trace :call do |tp|
    puts "Called method #{tp.method_id}"
    end
    

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14. line
    class
    end
    call
    return
    c_call
    c_return
    raise
    b_call
    b_return
    thread_begin
    thread_end
    fiber_switch
    TracePoint event types
    

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15. line
    class
    end
    call
    return
    c_call
    c_return
    raise
    b_call
    b_return
    thread_begin
    thread_end
    fiber_switch
    TracePoint event types
    

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16. ( Live coding session )
    

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17. Inception (2010) © Warner Bros.
    https://commons.wikimedia.org/wiki/File:Solar_eclipse_1878Jul29-Corona_Pikes_peak_Langley.png
    

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18. Stackdriver
    Debugger
    

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19. https://commons.wikimedia.org/wiki/File:Lunar_eclipse_al-Biruni.jpg
    Threads
    

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20. TracePoint.trace :call do |tp|
    puts "Called method #{tp.method_id}"
    end
    

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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);
    

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22. Ruby interface to
    thread-scoped
    TracePoint call?
    

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23. https://commons.wikimedia.org/wiki/File:Astronomy;_a_view_of_London_in_1748,_with_diagrams_of_an_ecl_Wellcome_V0024734.jpg
    Speed
    

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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
    

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26. Native
    breakpoint API?
    

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27. https://commons.wikimedia.org/wiki/File:Macrobius,_lunar_and_solar_eclipse.jpg
    Side effects
    

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28. Object state changes
    External side effects
    Side effects
    

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29. BYTE_CODE_BLACKLIST = %w(
    setinstancevariable
    setclassvariable
    setconstant
    setglobal
    defineclass
    opt_ltlt
    opt_aset
    opt_aset_with
    ).freeze
    

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30. C_METHOD_WHITELIST = %w(
    Array#+
    Array#-
    Array#==
    Array#any?
    Array#assoc
    Array#at
    Array#bsearch
    # etc...
    

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32. Immutability?
    

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33. Immutability?
    Code jails?
    

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34. Immutability?
    Code jails?
    Guilds??
    

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36. Debuggers (the basics)
    are straightforward!
    

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37. Ruby has partial
    support for debuggers
    

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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
    

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39. It's just Ruby
    

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40. Thanks for viewing!
    Daniel Azuma
    dazuma@gmail.com
    @danielazuma
    

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