From: Hugh Sasse <hgs@...>
Date: 2007-08-07T01:29:50+09:00
Subject: Re: Mac OSX singleton

On Tue, 7 Aug 2007, Fyodor wrote:

> This might be an actual bug in ruby itself. any comments?

In so far as your example shows no rails code....
> 
> ---------- Forwarded message ----------
> From: Rails Trac <trac@rubyonrails.org>
> Date: Aug 6, 2007 5:40 PM
> Subject: [Rails Trac] #9202: Mac OSX singleton
> To: undisclosed-recipients
> 
> 
> #9202: Mac OSX singleton
> ----------------------+-----------------------------------------------------
>  Reporter:  fygrave   |       Owner:  core
>    Type:  defect    |      Status:  new
>  Priority:  normal    |   Milestone:  1.x
> Component:  Railties  |     Version:  edge
>  Severity:  normal    |    Keywords:  rails singleton mac osx
> ----------------------+-----------------------------------------------------
>  There's a problem with Mac OSx singleton class. To make the story short,
>  the singleton doesn't work as singleton on mac osx platform. with every
>  request a new instance of the class is created.

What are you actually using to request a new instance?

>  mac-2:~/rails/app/models mac$ uname -a
>  Darwin mac-2.local 8.10.1 Darwin Kernel Version 8.10.1: Wed May 23
>  16:33:00 PDT 2007; root:xnu-792.22.5~1/RELEASE_I386 i386 i386
> 
>  rails gem version - 1.2.3
> 
>  to reproduce define a class:
> 
>  foo.rb in models which would look like this:
> 
>  class Foo
>    include Singleton
>    class << self; attr_accessor :Foopipe; end

That looks to me like you're creating an accessor for what is effectively
a class variable, visible from any instance of this class. 
> 
>    def initialize
>        @cmd = "/bin/sleep 2000"

that's the best part of an hour.  You have setup a race condition.

>        if  self.class.Foopipe == nil then
>            self.class.Foopipe = IO.popen(@cmd, "r+")
>            self.class.KMpipe.sync = true
>            self.class.Foopipe.write("something)
>            self.class.KMpipe.flush
>        end
>   end
> 

You create the first instance, and while it is being made, I presume,
given that you don't show code, that you try to create another, but since
the first one doesn't exist yet, you can start to create the second.

>  ... the rest of class is not relevant.
> 
>  Foopipe in this example never takes any value, and an instance of the

Never?  Even after 2000 seconds?  Where's your proof of this statement?

>  class (and running proccess that could be seen with ps .. ) is created
>  every time when the class is created and accessed...
> 
> --
> Ticket URL: <http://dev.rubyonrails.org/ticket/9202>
> Rails Trac <http://dev.rubyonrails.org>
> Ruby on Rails
> 

        Hugh