selfpipe.rb

#!/usr/bin/env ruby
puts Process.pid
SIGNAL_QUEUE = []
reader, writer = IO.pipe

[:INT, :QUIT, :KILL, :USR1].each do |signal|
  Signal.trap(signal) do
    writer.write_nonblock('.')
    SIGNAL_QUEUE << signal
  end
end

loop do
  case SIGNAL_QUEUE.pop
  when :INT
    puts "received INT"
    exit
  when :QUIT
    puts "received QUIT"
    exit
  when :KILL
    puts "received KILL, but won't quit"
  when :USR1
    puts "received USR1"
  else
    ready = IO.select([reader])
    if ready[0].include?(reader)
      reader.read_nonblock(1)
    end
  end
end