Ruby, trace, set_trace_func

rb_trace_func.rb

RubyVM::InstructionSequence.compile_option = {
  trace_instruction: false
  # This disables the `trace` VM instruction
}

count = lambda do
  @count ||= 0
  @count += 1
end

set_trace_func proc { |event, _, _, id, _, _|
  if id == :to_s && event == "c-call"
    count.call
  end
}

at_exit do
  puts "The method Fixnum#to_s was called #{@count} times" 
end

runner.bash

ruby -r ./rb_trace_func.rb test.rb

test.rb

100_000.times { |num| num.to_s }

Hi Kashyap - just took a quick look at this and yes, it's a bit odd. I still see the trace YARV instructions being generated by the compiler, even when trace_instruction is set to false. When I have time I'll do some C-level debugging to understand what's going on. It might be we misunderstand the way compile_options work, or maybe there's a bug in MRI.

Makes sense. Also, GH gists won't send notifications for comments :/ Didn't see this earlier, sorry.

FWIW, if I run the test/ruby/test_settracefunc.rb with the :trace_instruction set to false, it throws a bunch of errors mostly relating to some events that weren't generated. For example, line, c-return, and return don't get generated but c-call gets generated!