From: Joel VanderWerf <vjoel@...>
Date: 2006-07-06T07:21:42+09:00
Subject: Re: thread mystery

ara.t.howard@noaa.gov wrote:
> 
> any idea why this script slows downs drastically as it runs and seems to 
> leak
> memory?

No idea, except that it seems to be related to the thread creation 
(maybe because it's within the sync block). The following works around 
it, and is probably more efficient anyway. I guess the semantics are 
close to the original.

require 'sync'
require 'thread'

class Switch
   ON, OFF, NEITHER = true, false, nil

   def initialize state = OFF
     extend Sync_m
     @state = NEITHER
     @observers = []
   end

   def on!
     synchronize(:EX){
       warn 'on!'
       @state = ON
       notity_observers
     }
   end

   def off!
     synchronize(:EX){
       warn 'off!'
       @state = OFF
       notity_observers
     }
   end

   def notity_observers
     synchronize(:SH){
       @observers.each do |o|
         o.notify @state
       end
     }
   end

   def add_observer o
     synchronize(:EX){
       @observers << o
     }
   end
end

class SwitchToggle
   def initialize switch
     @switch = switch
     @switch.add_observer self
     @q = Queue.new
     Thread.new do
       loop {@q.pop.call}
     end
   end
   def notify of
     case of
       when Switch::ON
         later{ @switch.off! }
       when Switch::OFF
         later{ @switch.on! }
       else
         raise of.to_s
     end
   end
   def later(&bl)
     @q << bl
   end
end

switch = Switch.new
toggle = SwitchToggle.new switch

switch.on!

STDIN.gets


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