From: Adam Bender <abender@...>
Date: 2008-03-26T07:32:27+09:00
Subject: Re: thread.rb

On Tue, Mar 25, 2008 at 2:01 PM, MenTaLguY <mental@rydia.net> wrote:
>  I do agree that the following thread.rb operations need to directly
>  support timeouts, though:
>
>   ConditionVariable#wait

ConditionVariable#wait appears to support timeouts
(http://www.ruby-doc.org/stdlib/libdoc/monitor/rdoc/classes/MonitorMixin/ConditionVariable.html#M001018).
 Do they not work as expected?

I couldn't find the Scheduler gem, so I'm trying to hack something
together based your code example, but using Monitors.  It depends on
ConditionVariable#wait, so it could be totally broken.  I didn't
understand the point of the Reader class in your code, since only one
thread at a time can acquire the lock in pop.  This problem is closely
related to the example on page 146 of Pickaxe 2nd ed.

require 'monitor'

class MyQueue

  def initialize
    @values = []
    @values.extend(MonitorMixin)
    @cond = @values.new_cond
  end

  def push(value)
    @values.synchronize do
      @values.push value
      @cond.signal
    end
    self
  end

  def pop(timeout=nil)
    ret = nil
    @values.synchronize do
      t = Time.now
      @cond.wait(timeout)
      puts "waited #{Time.now - t}"
      ret = @values.shift unless @values.empty?
    end
    return ret
  end
end

q = MyQueue.new

consumers = (1..3).map do |i|
  Thread.new("consumer #{i}") do |name|
    begin
      obj = q.pop(5)
      puts "#{name} consumed #{obj.inspect}"
      sleep(rand(0.05))
    end until obj == :END_OF_WORK
  end
end

producers = (1..3).map do |i|
  Thread.new("producer #{i}") do |name|
    3.times do |j|
      sleep(1)
      q.push("Item #{j} from #{name}")
    end
  end
end

producers.each { |th| th.join }
consumers.size.times { q.push(:END_OF_WORK) }
consumers.each { |th| th.join }

The problem is that the wait() waits for timeout seconds, even when
something is in the queue.

Thanks for your help,

Adam