From: Edgardo Hames <ehames@...>
Date: 2004-05-08T00:33:40+09:00
Subject: Re: signaling another thread

Robert Klemme wrote:
 >
>> I'd take the ConditionVariable approach if I could, otherwise I don't
>> see why you can't use the Observer Paradigm. Maybe, I'm missing the 
>> point.
> 
> Hm, dunno how exactly you want to treat this with observer.  But you need
> some kind of thread synchronization anyway, even if you use observer.
> 
> Are you familiar with multithreaded applications?
> 

Condition variables, semaphores and monitors  grant you exclusive access 
to shared resources. That means only one thread will access a resource 
in a given moment.

The Observer Paradigm, allows an object to be notified when a certain 
event happens. Check the following heavily based on the example in "The 
Pragmatic Programmer's Guide" :-). I added a method m to the WarnLow 
Class that loops until it gets notified.

I hope it helps.
Ed

----8<--------8<--------8<--------8<----
require "observer"
 
 
 

class Ticker
   include Observable
   def run
     i = 0
     while (i < 130)
       changed(i > 70)
       notify_observers(Time.now, i)
       i = i + 1
     end
   end
end

class Warner
   def initialize(ticker, limit)
     @limit = limit
     ticker.add_observer(self)   # all warners are observers
   end
end
 

class WarnLow < Warner
   def m
     @i = 0
     loop do
       @i = @i + 1
     end
   end
   def update(time, price)       # callback for observer
     if price < @limit
       print "#@i #{time.to_s}: Price below #@limit: #{price}\n"
     end
   end
end
 
 
 

class WarnHigh < Warner
   def update(time, price)       # callback for observer
     if price > @limit
       print "+++ #{time.to_s}: Price above #@limit: #{price}\n"
     end
   end
end
 
 
 

ticker = Ticker.new()
Thread.new {
         wl = WarnLow.new(ticker, 80)
         wl.m
}
WarnHigh.new(ticker, 120)
ticker.run



-- 
Edgardo Hames
Consultor Inform�tico
Vates S.A. Ingenier�a de Software

ehames@vates.com
Tel: +54 +351 +4240133 int. 121
9 de Julio 228 - 6� piso. C�rdoba