From: Brian Candler <b.candler@...>
Date: 2009-05-14T20:40:40+09:00
Subject: Re: JRuby 1.3.0 will include Nailgun

Brian Candler wrote:
> I don't see in principle why it couldn't be done - I guess you just fork 
> the process when a request comes in. The messy bit is passing the 
> stdin/stdout/stderr file descriptors over a socket. And it could be 
> called "railgun" :-)

It turns out all the messy passing of IO objects is already included in 
the Ruby standard socket library, so without further ado, here's a 
working proof-of-concept :-) Tested under ruby 1.8.6p111

$ cat hello.rb
# Silly program which requires active_support to work
puts ''.blank?

$ time ruby -rubygems -e'require "active_support"' -e 'load "hello.rb"'
true

real  0m1.522s
user  0m1.280s
sys  0m0.216s

$ ruby -rubygems -railgun -e'require "active_support"'
Railgun PID 10272 started

[in another console]
$ time ./rg 10272 hello.rb
true

real  0m0.076s
user  0m0.036s
sys  0m0.012s

---- 8< ---- ailgun.rb ----
# Sample usage:
#    ruby -rubygems -railgun -e'require "active_support"'
# Note that at least one '-e' option is required, e.g. -e0

at_exit do
  require 'socket'
  sockname = "/tmp/railgun#{$$}"
  File.delete(sockname) rescue nil
  trap('INT') { File.delete(sockname) rescue nil; exit! }
  server = UNIXServer.open(sockname)
  puts "Railgun PID #{$$} started"
  while client = server.accept
    fork do
      begin
        STDIN.reopen(client.recv_io)
        STDOUT.reopen(client.recv_io)
        STDERR.reopen(client.recv_io)
        # [script, args] # TODO: interpret flags like -I and -r
        nbytes = client.read(4).unpack("N").first
        args = Marshal.load(client.read(nbytes))
        client.close
        cmd = args.shift
        ARGV.replace(args)
        load cmd
      rescue Exception => e
        STDERR.puts e
        client.close rescue nil
      end
    end
    client.close
  end
end
---- 8< ----

---- 8< ---- rg.rb ----
#!/usr/bin/env ruby
# Usage:  ruby rg.rb <pid> <cmd> <args...>

require 'socket'
pid = ARGV.shift
server = UNIXSocket.open("/tmp/railgun#{pid}")
args = Marshal.dump(ARGV)
server.send_io(STDIN)
server.send_io(STDOUT)
server.send_io(STDERR)
server.write [args.size].pack("N")
server.write args
---- 8< ----

The awkward thing from a user point of view is that you have to remember 
the pid of where the railgun server is. You could use a fixed name, but 
that would only let you have a single railgun process preloaded with a 
single set of libraries.

Perhaps it would be better for the railgun server to drop you into a new 
shell which has something in the ENV with this information.
-- 
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