From: Joel VanderWerf <vjoel@...>
Date: 2005-08-10T10:16:05+09:00
Subject: Re: drb server using file/tail to read file, and update client?

Joel VanderWerf wrote:
> Ryan Leavengood wrote:
> 
>>Christopher Aldridge said:
>>
>>
>>>Any suggestions or am I doing it the only way it can be done?
>>
>>
>>If I understand your problem correctly, the issue is that you now have to
>>constantly poll the server to see if there are more lines, when really
>>what you want is to have the server tell the clients of the new lines.
>>
>>So your options are either to code the clients so they also have a DRb
>>server, which the server connects to when outputting lines from the log
>>file, or possible to use Rinda and a Tuplespace.
> 
> 
> IIRC, the client can also call a method with a block. The block is
> undumped, so it remains on the client side, with a proxy on the server
> side. When the server's implementation of the method yields to the
> block, it calls the code on the client side. DRb is sooo elegant!
> 
> An example of that idea is embedded in a little distributed chat server
> example that comes with my foxtails project, using distributed observers
> wired up to fox gui widgets. But it's probably easier to code this up
> from scratch, once you know that DRb supports distributed block yields.
> 

Here is an example of using callbacks by yielding from the server:

==== svr.rb ====
require 'drb'

$callback = nil

class C
  def foo
    3.times do |i|
      yield i
    end
  end

  def bar(&pr)
    $callback = pr
  end
end

obj = C.new

DRb.start_service('druby://:22337', obj)

begin
  loop do
    $callback.call if $callback
    sleep 1
  end
rescue DRb::DRbConnError
  puts "client is gone"
end
=========

==== clnt.rb ====
require 'drb'

DRb.start_service()
obj = DRbObject.new_with_uri('druby://:22337')

obj.foo do |i|
  p i
end

obj.bar do
  puts "Got callback!"
end

puts "press return to quit"
gets
========

output:

0
1
2
press return to quit
Got callback!
Got callback!
Got callback!
Got callback!

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