fearless_fool fearless_fool - 7 months ago 11
Ruby Question

How do I configure ruby to enter the debugger on Ctrl-C (SIGINT)?

I'd like to enter the debugger upon typing ctrl-C (or sending a SIGINT). I have installed the debugger (I'm running Ruby 1.9.3) and verified that it works. I've added this to my setup files (this is for Padrino, but I assume it would be similar for Rails):

# file: config/boot.rb
Padrino.before_load do
trap("SIGINT") { debugger } if Padrino.env == :development
end


... but typing Ctrl-C does not invoke the debugger. In fact, if I replace
debugger
with
puts "saw an interrupt!"
, typing Ctrl-C doesn't cause a print to happen either.

update



Following this suggestion from Mike Dunlavey, I tried explicitly calling
catch Interrupt
from within the debugger:

$ rdebug `which padrino` console
^Z^Z$HOME/usr/bin/padrino:9
require 'rubygems'
(rdb:1) catch Interrupt
Catch exception Interrupt.
(rdb:1) c
=> Loading development console (Padrino v.0.10.7)
=> Loading Application BlueDotAe
=> Loading Application Admin
irb(main):001:0> C-c C-c^C
irb(main):001:0>


No joy -- interrupt did not enter the debugger.

What am I missing?

Answer

If you want to trap SIGINT while running in the console, the short answer is: you cannot unless you monkey-patch IRB. Every Ruby app (whether padrino, or rails or whatnot) that uses the console will end up calling usr/lib/ruby/1.9.1/irb.rb, and in IRB.start, it does:

trap("SIGINT") do
  irb.signal_handle
end

... just before entering the main loop. This will override any trap("SIGINT") you might have put in your startup code.

But if you want to trap SIGINT in a script file (for example, if you want to profile your code as described by Mike Dunlavey here), you can create a script file such as:

# File: profile_complex_operation.rb
trap("SIGINT") { debugger }
MyApp.complex_operation

and then invoke it as in:

$ ruby profile_complex_operation.rb

Now, when you hit ^C (or send SIGINT from another process), it will enter the debugger.

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