Call a method with block on distributed object (drb)

Ruby
1

Hi.
I’ve the follow class for a distributed object:

class Counter
  def initialize(i = 0)
    @index = i
  end
  def increment
    @index += 1
  end
  def current
     return @index
  end
  def each(n = 1)
    threads = []
    n.times do
      threads << Thread.new do
        yield(self.current)
      end
    end
    threads.map(&:join)
  end
end

Now the server:

require 'drb'
require './counter.rb'

DRb.start_service('druby://127.0.0.1:9000', Counter.new)
puts "Wordlist server running at #{DRb.uri}"
trap('SIGINT') { DRb.stop_service }
DRb.thread.join

And the client:

require 'drb'

c = DRbObject.new_with_uri('druby://127.0.0.1:9000')
c.each(8) do |i|
  puts i
end

I run the server (ok) and then the client and I get the follow error:

/Users/pioz/.rvm/rubies/ruby-2.0.0-p0/lib/ruby/2.0.0/drb/drb.rb:1687:in

current_server': DRb::DRbServerNotFound (DRb::DRbConnError) from /Users/pioz/.rvm/rubies/ruby-2.0.0-p0/lib/ruby/2.0.0/drb/drb.rb:1756:into_id’
from
/Users/pioz/.rvm/rubies/ruby-2.0.0-p0/lib/ruby/2.0.0/drb/drb.rb:1071:in
initialize' from /Users/pioz/.rvm/rubies/ruby-2.0.0-p0/lib/ruby/2.0.0/drb/drb.rb:647:innew’
from
/Users/pioz/.rvm/rubies/ruby-2.0.0-p0/lib/ruby/2.0.0/drb/drb.rb:647:in
make_proxy' from /Users/pioz/.rvm/rubies/ruby-2.0.0-p0/lib/ruby/2.0.0/drb/drb.rb:564:inrescue in dump’
from
/Users/pioz/.rvm/rubies/ruby-2.0.0-p0/lib/ruby/2.0.0/drb/drb.rb:561:in
dump' from /Users/pioz/.rvm/rubies/ruby-2.0.0-p0/lib/ruby/2.0.0/drb/drb.rb:610:insend_request’
from
/Users/pioz/.rvm/rubies/ruby-2.0.0-p0/lib/ruby/2.0.0/drb/drb.rb:921:in
send_request' from /Users/pioz/.rvm/rubies/ruby-2.0.0-p0/lib/ruby/2.0.0/drb/drb.rb:1221:insend_message’
from
/Users/pioz/.rvm/rubies/ruby-2.0.0-p0/lib/ruby/2.0.0/drb/drb.rb:1110:in
block (2 levels) in method_missing' from /Users/pioz/.rvm/rubies/ruby-2.0.0-p0/lib/ruby/2.0.0/drb/drb.rb:1197:inopen’
from
/Users/pioz/.rvm/rubies/ruby-2.0.0-p0/lib/ruby/2.0.0/drb/drb.rb:1109:in
block in method_missing' from /Users/pioz/.rvm/rubies/ruby-2.0.0-p0/lib/ruby/2.0.0/drb/drb.rb:1128:inwith_friend’
from
/Users/pioz/.rvm/rubies/ruby-2.0.0-p0/lib/ruby/2.0.0/drb/drb.rb:1108:in
method_missing' from client.rb:5:in’

Why?
If I change the client in this way:

require 'drb'
require 'mechanize'

c = DRbObject.new_with_uri('druby://127.0.0.1:9000')
threads = []
8.times do
  threads << Thread.new do
    puts c.current
  end
end
threads.map(&:join)

all works fine.
Any idea or help?

2

On 07/16/2013 06:35 AM, Enrico P. wrote:

Hi.
…

 /Users/pioz/.rvm/rubies/ruby-2.0.0-p0/lib/ruby/2.0.0/drb/drb.rb:1687:in

`current_server’: DRb::DRbServerNotFound (DRb::DRbConnError)

Insert this line at the beginning of your client:

DRb.start_service

The server is trying to yield to code on the client. This is the same as
sending #call to a remote proc in the client. As with any remote method
call, there has to be a listening drb server in the client.

3

Please keep in mind if you pass a block to a remote object, the block
will
still be executed locally, and the results of the block invocation sent
back to the remote object.