From: m_seki@...
Date: 2002-11-28T08:14:20+09:00
Subject: Re: DRb & Threads ...


Hi, 

> Currently, I am only retrieving data with my DRb client, but this will
> change in the near future. If I am updating the data class via the DRb
> client, I assume I will need to take precautions to protect the data class?

> If you use a mutex in this situation, whom gets blocked by the mutex and how
> does it effect the DRb operation/client? 

Yes, you need it and work well.

# count.rb
require 'thread'

class Counter
  def initialize(n = 0)
    @value = n
  end
  attr_reader :value
  alias :to_i :value

  def succ
    it = @value
    sleep 0.5
    @value = it + 1
    puts @value
    return @value
  end
end

class MutexCounter < Counter
  def initialize(n = 0)
    super(n)
    @mutex = Mutex.new
  end
  
  def succ
    @mutex.synchronize do
      return super
    end
  end
end

if __FILE__ == $0
  require 'drb/drb'
  
  class Counter
    include DRbUndumped
  end
  
  here = ARGV.shift || 'druby://localhost:12345'

  front = Hash.new
  front[:Counter] = Counter.new
  front[:MutexCounter] = MutexCounter.new

  DRb.start_service(here, front)
  puts DRb.uri
  DRb.thread.join
end
  

# test_count.rb
require 'drb/drb'

def test(counter, n = 10)
  n.times do |i|
    puts "#{i}: #{counter.succ}"
  end
end

there = ARGV.shift || 'druby://localhost:12345'

DRb.start_service
front = DRbObject.new(nil, there)

puts "Counter"
test(front[:Counter])

puts "MutexCounter"
test(front[:MutexCounter])


-----
run scripts.

Terminal 1
% ruby count.rb

Terminal 2 and 3
% ruby test_countr.b


Terminal 2                 Terminal 3
----------                 ----------
Counter                    Counter
0: 1                       0: 2
1: 2                       1: 3
2: 3                       2: 4
3: 4                       3: 5
4: 5                       4: 6
5: 6                       5: 7
6: 7                       6: 8
7: 8                       7: 9
8: 9                       8: 10
9: 10                      9: 11
MutexCounter               MutexCounter
0: 1                       0: 2
1: 3                       1: 4
2: 5                       2: 6
3: 7                       3: 8
4: 9                       4: 10
5: 11                      5: 12
6: 13                      6: 14
7: 15                      7: 16
8: 17                      8: 18
9: 19                      9: 20