From: Lars Christensen <larsch@...>
Date: 2008-06-30T21:17:16+09:00
Subject: Re: Why can't I return "Threads.list" Array in DRb?

On Jun 29, 7:00 pm, Iñaki Baz Castillo <i...@aliax.net> wrote:
> El Domingo, 29 de Junio de 2008, Iñaki Baz Castillo escribió:
> > El Domingo, 29 de Junio de 2008, Iñaki Baz Castillo escribió:
> > > but instead of an Array object I get a DRb::DRbObject, and in each call
> > > to this method I get a different "id":
>
> Well, I am understanding that if DRb server return an object unknown for the
> DRb client, the the only way the client hast to use/show it is as raw value,
> is it?

It seems more like a situation where DRb detects that the return
object (the Array) is not fully serializable (contains non-
derializable objects), and hence it returns a "server reference" or
"proxy object" for the object instead. Whenever you invoke method on
the proxy object, they are invoked on the server.

This is really the beauty of DRb: Objects that can't be marshalled /
serialized, become remote objects automatically. You can even 'yield'
to blocks on the client, which is what happens when you "puts" the
array.

Here's a simpler example:

class Thing
  include DRb::DRbUndumped # make sure instance are not marshalled and
transferred
  def each
    puts "each called on server"
    3.times { |i| yield(i) }
  end
end
class Server
  def create_thing
    Thing.new
  end
end
DRb::start_service("druby://:12000", Server.new)
DRb.thread.join

And a client:

DRb.start_service
remoteServer = DRb::DRbObject.new(nil, "druby://localhost:12000")
remoteThing = remoteServer.create_thing
remoteThing.each { |i| p i }

The 'remoteThing' becomes a DRb::DRbObject which serves as a proxy to
the Thing object on the server. Thing#each is actally run on the
server and yields back to the block on the client.

Lars