From: Hugh Sasse <hgs@...>
Date: 2006-07-06T18:32:57+09:00
Subject: Re: thread mystery

On Thu, 6 Jul 2006, ara.t.howard@noaa.gov wrote:

> 
> any idea why this script slows downs drastically as it runs and seems to leak
> memory?

I'm not familiar with enough with sync to answer this I suspect, esp. the
memory part, but....
> 
> 
> require 'sync'
> 
> class Switch
>   ON, OFF, NEITHER = true, false, nil
> 

...in here: 
>   def initialize state = OFF
>     extend Sync_m
>     @state = NEITHER
>     @observers = []
>   end

state is not used.  Should that be
      @state = state
otherwise the default OFF doesn't agree with @state being set 
to NEITHER.
> 
>   def on!
>     synchronize(:EX){
>       warn 'on!'
>       @state = ON
>       notity_observers
>     }
>   end
> 
>   def off!
>     synchronize(:EX){
>       warn 'off!'
>       @state = OFF
>       notity_observers
>     }
>   end

so both on! and off! notify_observers, however many....
> 
>   def notity_observers
>     synchronize(:SH){
>       @observers.each do |o|
>         o.notify @state
>       end
>     }
>   end

so could you have a thread for each observer?
> 
>   def add_observer o
>     synchronize(:EX){
>       @observers << o
>     }
>   end
> end
> 
> class SwitchToggle
>   def initialize switch
>     @switch = switch
>     @switch.add_observer self
>   end
>   def notify of
>     case of
>       when Switch::ON
>         Thread.new{ @switch.off! }
>       when Switch::OFF
>         Thread.new{ @switch.on! }
>       else
>         raise of.to_s
>     end
>   end
> end
> 
> switch = Switch.new
> toggle = SwitchToggle.new switch
> 
> switch.on!

Not sure what happens when the synchronize is called within itself,
because synchronize calls notity_observers which calls @switch.on! 
which calls synchronize which calls notity_observers.... 

Not spend enough time to really grok this though.
> 
> STDIN.gets
> 

        Hugh