From: 7stud -- <dolgun@...>
Date: 2007-10-07T20:31:52+09:00
Subject: Re: Multitasking and collecting results

Greg Willits wrote:
> Greg Willits wrote:
>> I've put together this
>> little outline, but the results always come back in order when I believe
>> useing sleep should randomize them, so I'm suspicioius that I'm not
>> really getting async processing out of my code.
> 
> Oh wait, they're in order because that's the order I have them inserted 
> into @results. Duh.
> 
> I confirmed async by putting a timer wrapper around the whole thing, and 
> indeed it completes in less time than the sum of each task's pause time.
> 

Try the following to see some random order in the results. The threads 
in the code enter their data in a
Queue (located in the 'thread' module in the Standard Library).  A Queue 
enables you to pass data between threads in a "thread-safe manner".  A 
"thread safe manner" means that only one thread can access the Queue at 
the same time.  A Queue guarantees that two threads can't access the 
Queue at the same time, so the data cannot get scrambled.

require 'thread'

class TaskManager

  attr_reader :results

  def initialize(*task_params)
    @task_params = task_params
    @results = Queue.new
  end

  def start_producers
    threads = []

    @task_params.each_with_index do |param, indx|
      threads[indx] = Thread.new do
        @results << Task.new.do_stuff(param)
      end
    end

    threads.each {|thred| thred.join}
  end
end

class Task
  def do_stuff(x)
    pause = rand() * 4
    sleep pause

    "handing back #{x}, #{pause}"
  end
end

task_mngr = TaskManager.new('one', 'two', 'three')
task_mngr.start_producers
num_results = task_mngr.results.length
num_results.times {puts task_mngr.results.pop}



Note that rand(.1) is the same as rand(), so I don't know why pickaxe2 
uses rand(.1).

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