From: Robert Klemme <shortcutter@...>
Date: 2011-05-13T17:42:20+09:00
Subject: Re: help on threads synchronization

On Fri, May 13, 2011 at 9:33 AM, Zd Yu <zdyu2000@gmail.com> wrote:
> How to make two threads do something in turn, i.e., A => B => A => B
> ....?
>
> I know the code below is not correct, but I do not know how to make it
> correct. Could anybody help?
>
> =======================================
> mutex=Mutex.new
>
> t=Thread.new {
>  while true
>    Thread.stop
>    puts "B move..."
>    Thread.main.wakeup
>  end
> }
>
> while true
>  puts "A move..."
>  t.wakeup
>  Thread.stop
> end

Since you want to have one thread active at a time only this is not a
case for threads.  If at all you might use Fibers:

http://www.rubyinside.com/ruby-fibers-8-useful-reads-on-rubys-new-concurrency-feature-1769.html
http://www.ruby-doc.org/core-1.9/classes/Fiber.html

The simplest solution is to code interchanges directly:

Actor = Struct.new :number do
  def alive?; rand(10) != 0 end

  def step
    printf "Actor %p working...\n", number
  end
end

acts = Array.new(2) {|i| Actor.new i }

until acts.empty?
  acts.delete_if do |a|
    a.step
    !a.alive?
  end
end

Kind regards

robert

-- 
remember.guy do |as, often| as.you_can - without end
http://blog.rubybestpractices.com/