From: Wes Gamble <weyus@...>
Date: 2006-07-11T06:10:59+09:00
Subject: Re: Best way to synchronize access to a method?

Simon Kr旦ger wrote:
> Wes Gamble wrote:
>>>
>>> Thanks,
>> Thanks,
>> Wes
> 
> You have several problems in your code you may want to look at before 
> thinking
> about Threads:
> 
> * myClass has to be spelled MyClass (see Constants in Ruby)
> 
> * get_max_value isn't a class method (use self.get_max_value if you want 
> such)
> 
> * max_value is only defined inside the block, so you get
>   "undefined local variable or method `max_value' for MyClass:Class"
> 
> * if you define it as class method the interpreter will show you
>   "undefined method `synchronize' for MyClass:Class" because synchronize
>   isn't a class method
> 
> * most of the time when the documentation is saying "it is essential 
> to..."
>   it is there for a reason
> 
> I don't want to be harsh, but it would be nice to let the interpreter 
> find
> the obvious bugs it is able to find.
> 
> maybe that is what you want:
> 
> require 'thread'
> 
> class MyClass
>   @@mutex = Mutex.new
> 
>   def self.do_select_to_get_max_value;
>     42
>   end
> 
>   def self.get_max_value
>     @@mutex.synchronize do
>       return do_select_to_get_max_value
>     end
>   end
> end
> 
> p MyClass::get_max_value
> 
> cheers
> 
> Simon


Simon,

Thanks for the feedback.  The code below appears to work.  Do you agree 
that the code will be sychronized on the class object itself?

=====================

require 'monitor'

class Job < ActiveRecord::Base
  self.extend(MonitorMixin)

....

  public
  def self.get_next_job_number
    max_value = nil
    synchronize {
      max_value = self.find(:first, :select => 'MAX(AbsJobNumber) AS 
max').max
    }
    max_value.to_i + 1
  end
end

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