Simple Ruby app preloader.

ruby_preload

#!/usr/bin/env ruby
require "socket"

# This is a simple preloader for Ruby apps.
# Usage:
# Put this file somewhere in your PATH, named 'ruby_preloader' and make sure
# it's executable.
# Add whatever you need to load your app environment to a .preload.rb in the
# base directory of your project.
# Add #!/usr/bin/env ruby_preload as the first line of any script you want to
# run with a preloaded environment.
# Run, and keep running, 'ruby_preload' from the base directory of your project.
# Run your script, it should now load quickly.

script = ARGV.last
exec("ruby", "--version") if script == "--version"
script, reload = nil, true if script == "--reload"

Dir.mkdir("/tmp/ruby_preload") unless File.exist?("/tmp/ruby_preload")
sock_path = "/tmp/ruby_preload/#{Dir.pwd.tr("^a-zA-Z0-9", "_")}_sock"

std_io = [STDIN, STDOUT, STDERR]

if script
  abort("ruby_preload server not running") unless File.exist?(sock_path)
  sock = UNIXSocket.new(sock_path)
  sock.puts(script)
  pid = sock.gets.to_i
  (Signal.list.keys - %W{ILL FPE BUS SEGV VTALRM KILL STOP}).each do |name|
    Signal.trap(name) {Process.kill(name, pid)}
  end
  std_io.each {|io| sock.send_io(io)}
  exit(sock.gets.to_i)
else
  server = UNIXServer.new(sock_path)
  begin
    require "#{Dir.pwd}/.preload" if File.exist?(".preload.rb")
  rescue Exception => e
    File.unlink(sock_path)
    raise
  end
  is_parent = true
  while is_parent
    begin
      sock = server.accept
      script = sock.gets.chomp
      is_parent = fork
      File.unlink(sock_path) && exec($0, "--reload") if is_parent && reload
    rescue Exception => e
      File.unlink(sock_path)
      Interrupt === e ? exit : raise
    end
  end
  server.close
  sock.puts(Process.pid)
  std_io.each {|io| io.reopen(sock.recv_io)}
  begin
    load script
  ensure
    sock.puts($! ? $!.respond_to?(:status) ? $!.status : 1 : 0)
  end
end