Wsrtjtyk

The following example is given in the book Programming Ruby 1.9 & 2.0:

require 'irb'



trap "INT" do

  IRB.start

end



count = 0

loop do

  count += 1

  puts count

  puts "Value = #{@value}" if defined? @value

  sleep 1

end

Unfortunately, if I run this code with my Ruby 2.5.1 setup I get the following ThreadError (run_irb.rb is the name of the file with the code above):

    24: from run_irb.rb:8:in `<main>'

    23: from run_irb.rb:8:in `loop'

    22: from run_irb.rb:12:in `block in <main>'

    21: from run_irb.rb:12:in `sleep'

    20: from run_irb.rb:4:in `block in <main>'

    19: from /usr/lib/ruby/2.5.0/irb.rb:376:in `start'

    18: from /usr/lib/ruby/2.5.0/irb/init.rb:17:in `setup'

    17: from /usr/lib/ruby/2.5.0/irb/init.rb:112:in `init_config'

    16: from /usr/lib/ruby/2.5.0/irb/init.rb:112:in `new'

    15: from /usr/lib/ruby/2.5.0/irb/locale.rb:32:in `initialize'

    14: from /usr/lib/ruby/2.5.0/irb/locale.rb:108:in `load'

    13: from /usr/lib/ruby/2.5.0/irb/locale.rb:124:in `find'

    12: from /usr/lib/ruby/2.5.0/irb/locale.rb:145:in `search_file'

    11: from /usr/lib/ruby/2.5.0/irb/locale.rb:157:in `each_localized_path'

    10: from /usr/lib/ruby/2.5.0/irb/locale.rb:167:in `each_sublocale'

     9: from /usr/lib/ruby/2.5.0/irb/locale.rb:158:in `block in each_localized_path'

     8: from /usr/lib/ruby/2.5.0/irb/locale.rb:150:in `block in search_file'

     7: from /usr/lib/ruby/2.5.0/rubygems.rb:213:in `try_activate'

     6: from /usr/lib/ruby/2.5.0/rubygems/specification.rb:1063:in `find_by_path'

     5: from /usr/lib/ruby/2.5.0/rubygems/specification.rb:1063:in `find'

     4: from /usr/lib/ruby/2.5.0/rubygems/specification.rb:1063:in `each'

     3: from /usr/lib/ruby/2.5.0/rubygems/specification.rb:1064:in `block in find_by_path'

     2: from /usr/lib/ruby/2.5.0/rubygems/core_ext/kernel_require.rb:40:in `require'

     1: from /usr/lib/ruby/2.5.0/monitor.rb:185:in `mon_enter'

/usr/lib/ruby/2.5.0/monitor.rb:185:in `lock': can't be called from trap context (ThreadError)

Is there a way to get the irb run from the trap context with Ruby 2.5.1?

Ruby 2.0 does not allow Mutex#lock within a signal handler

According to this bug 7917 in ruby lang this is the "expected" behaviour. So you've basically found a language bug and a book bug because the author didn't test this example in ruby 2.0 (confirmed that it works in 1.9.)

An alternative method is to use an exception/rescue and execute an IRB session from an interrupt like this:

require 'irb'



count = 0

loop do

  count += 1

  puts count

  puts "Value = #{@value}" if defined? @value

  sleep 1

rescue Interrupt => e

  IRB.start

  break

end 

The above will correctly trap an interrupt and allow an IRB session to start. I did notice that IRB.start won't give you a local execution context, so you may want to look at binding.irb that let's you start a more useful debugging session like this:

$ ruby thread-test.rb

1

2

^C

[1] irb(main)>



From: /work/_scratch/thread-test/thread-test.rb @ line 11 :



     6:   puts count

     7:   puts "Value = #{@value}" if defined? @value

     8:   sleep 1

     9: rescue Interrupt => e

    10:   binding.irb

 => 11:   break

    12: end



[2] irb(main)> e

=> Interrupt

[3] irb(main)> count

=> 2

I found a few blog posts on handling Signals, Traps, and Rescues and Graceful Shutdown that may help you further with your problem.