Append (<<) to Array attributes of DRb objects?

ruby-talk
1

When working locally with an object whose attribute is meant to store
an array, I have no problem making calls like:

object.items << new_item

If I try to do the same thing with a DRb object, though, appending has
no effect on the remote object. I've distilled the problem down to
this example...

My server:

require 'drb'
class TestServer
attr_accessor :items
def initialize
  @items = []
end
def add_item(item)
  @items << item
end
def add
  sum = 0
  @items.each {|item| sum += item}
  sum
end
end
server = TestServer.new
DRb.start_service('druby://localhost:9000', server)
DRb.thread.join

My client:

require 'drb'
DRb.start_service()
obj = DRbObject.new(nil, 'druby://localhost:9000')
obj.items << 1 #No effect.
obj.items << 2 #No effect.
items = [1, 2]
obj.items = items #Works.
obj.add_item(1) #Works.
obj.add_item(2) #Works.
puts obj.add #Gives '6' instead of '9'.

I'd rather my client programs be able to use append (<<) instead of an
add_item(item) method or direct assignment. How can I do this?

2

Jay McGavren wrote:

When working locally with an object whose attribute is meant to store
an array, I have no problem making calls like:

object.items << new_item

If I try to do the same thing with a DRb object, though, appending has
no effect on the remote object.

The #items method returns an Array. That Array is not DRbUndumped (i.e., not a proxy object), so it gets _copied_ back to the client. Modifying that copy in the client can't affect the original in the server.

Your #add_item method is a good way around this.

Or, you could extend the array with DRbUndumped, to keep it on the server.

···

--
       vjoel : Joel VanderWerf : path berkeley edu : 510 665 3407

3

Jay McGavren wrote:

When working locally with an object whose attribute is meant to store
an array, I have no problem making calls like:

object.items << new_item

If I try to do the same thing with a DRb object, though, appending has
no effect on the remote object. I've distilled the problem down to
this example...

The BackgrounDRb mailing list will give you better odds of a good answer.

In general, I treat my background threads with the strictest isolation, and I don't go passing arrays back and forth. Consider the marshalling that must occur just for one stinkin' <<. So I don't know the answer to your question, even though I have used BackgrounDRb on 2 projects so far...

···

--
  Phlip
  Test Driven Ajax (on Rails) [Book]
  "Test Driven Ajax (on Rails)"
  assert_xpath, assert_javascript, & assert_ajax

4

Note that he is not using BackgroundDRb, but DRb itself, so I believe
this list is the most appropriate.

You should probably just extend the array with DRbUndumped, that will
(IIRC) speed up the appending, and allow << to work properly.

···

On 7/29/07, Phlip <phlip2005@gmail.com> wrote:

The BackgrounDRb mailing list will give you better odds of a good answer.

In general, I treat my background threads with the strictest isolation, and
I don't go passing arrays back and forth. Consider the marshalling that must
occur just for one stinkin' <<. So I don't know the answer to your question,
even though I have used BackgrounDRb on 2 projects so far...

--
  Phlip

--
Chris Carter
concentrationstudios.com
brynmawrcs.com

5

Thusly, yes?

Server:

  require 'drb'
  class UndumpedArray < Array
    include DRbUndumped
  end
  class TestServer
    attr_accessor :items
    def initialize
      @items = UndumpedArray.new
    end
    def add
      sum = 0
      @items.each {|item| sum += item}
      sum
    end
  end
  server = TestServer.new
  DRb.start_service('druby://localhost:9000', server)
  DRb.thread.join

Client:

  require 'drb'
  DRb.start_service()
  obj = DRbObject.new(nil, 'druby://localhost:9000')
  obj.items << 1
  obj.items << 2
  puts obj.add #Gives '3'.

Seems to work pretty well. DRbUndumped may be the solution to my
concerns about network overhead as well.

Thanks to everyone for the assistance!

-Jay

···

On Jul 30, 8:33 am, "Chris Carter" <cdcar...@gmail.com> wrote:

You should probably just extend the array with DRbUndumped, that will
(IIRC) speed up the appending, and allow << to work properly.

6

You should probably just extend the array with DRbUndumped, that will
(IIRC) speed up the appending, and allow << to work properly.

Thusly, yes?

Server:

  require 'drb'
  class UndumpedArray < Array
    include DRbUndumped
  end
  class TestServer
    attr_accessor :items
    def initialize
      @items = UndumpedArray.new

Get rid of UndumpedArray.

@items = Array.new
@items.extend DRbUndumped

···

On Jul 30, 2007, at 13:35, Jay McGavren wrote:

On Jul 30, 8:33 am, "Chris Carter" <cdcar...@gmail.com> wrote:

    end
    def add
      sum = 0
      @items.each {|item| sum += item}
      sum
    end
  end
  server = TestServer.new
  DRb.start_service('druby://localhost:9000', server)
  DRb.thread.join

Client:

  require 'drb'
  DRb.start_service()
  obj = DRbObject.new(nil, 'druby://localhost:9000')
  obj.items << 1
  obj.items << 2
  puts obj.add #Gives '3'.

Seems to work pretty well. DRbUndumped may be the solution to my
concerns about network overhead as well.

Thanks to everyone for the assistance!

-Jay

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