Dump backtrace of all threads in ruby

I have created a few lines of code that allow me to dump stacktrace/backtrace of all threads of a running ruby process. If ruby support Thread#backtrace then it will print backtrace of all threads otherwise it will print of current running thread.
To use it first create a file ruby_backtrace.rb with the following content

require 'pp'

def backtrace_for_all_threads(signame)
  File.open("/tmp/ruby_backtrace_#{Process.pid}.txt","a") do |f|
      f.puts "--- got signal #{signame}, dump backtrace for all threads at #{Time.now}"
      if Thread.current.respond_to?(:backtrace)
        Thread.list.each do |t|
          f.puts t.inspect
          PP.pp(t.backtrace.delete_if {|frame| frame =~ /^#{File.expand_path(__FILE__)}/},
               f) # remove frames resulting from calling this method
        end
      else
          PP.pp(caller.delete_if {|frame| frame =~ /^#{File.expand_path(__FILE__)}/},
               f) # remove frames resulting from calling this method
      end
  end
end

Signal.trap(29) do
  backtrace_for_all_threads("INFO")
end

Then require this file to your ruby script you want to inspect e.g. t2.rb

require 'thread'
require './ruby_backtrace'

def foo
   bar
end

def bar
   sleep 100
end

thread1 = Thread.new do
   foo
end

thread2 = Thread.new do
   sleep 100
end

thread1.join
thread2.join

Finally run the script, send INFO signal to it and look at file ruby_backtrace_pid.txt, where pid is process id

$ ruby t2.rb &
[2] 4719
$ kill -29 4719
$ kill -29 4719
$ cat /tmp/ruby_backtrace_4719.txt 
--- got signal INFO, dump backtrace for all threads at 2012-04-07 17:33:14 +0200
#
["t2.rb:21:in `call'", "t2.rb:21:in `join'", "t2.rb:21:in `
'"]
#
["t2.rb:9:in `bar'", "t2.rb:5:in `foo'", "t2.rb:13:in `block in 
'"]
#
["t2.rb:17:in `block in 
'"]
--- got signal INFO, dump backtrace for all threads at 2012-04-07 17:33:15 +0200
#
["t2.rb:21:in `call'", "t2.rb:21:in `join'", "t2.rb:21:in `
'"]
#
["t2.rb:9:in `bar'", "t2.rb:5:in `foo'", "t2.rb:13:in `block in 
'"]
#
["t2.rb:17:in `block in 
'"]