From: ara.t.howard@...
Date: 2006-06-08T03:49:24+09:00
Subject: Re: how do I impose a method call delay?

On Thu, 8 Jun 2006, Jason Sallis wrote:

> I've got a simple Ruby class that has one method which uses open-uri to pass
> a request to a remote server and retrieve an xml document containing some
> server statistics.  Nothing too exciting and it's working fine.  The
> administrator has asked that we limit our calls to once every 30 seconds to
> avoid hammering the server.  I'd like to bake this forced delay right into
> my class so that if another application is using it and tries to make 2
> calls within 30 seconds, the second call is delayed until the 30 second time
> period is up.  Any ideas on how I could approach this?

here's an idea for a thread-safe impl:


harp:~ > cat a.rb
#! /usr/bin/env ruby
require 'sync'

module Delay
   module ClassMethods
     def delay m, t
       m, t = m.to_s, t.to_f
       dm = "__delayed_#{ m }__"
       module_eval <<-code
         alias_method "#{ dm }", "#{ m }"
         def #{ m }(*a, &b)
           __delay_init__
           __delay__("#{ m }"){ #{ dm }(*a, &b) }
         end
       code
       __delay_time__[m] = t
     end
     def __delay_last__() @__delay_last__ ||= {} end
     def __delay_time__() @__delay_time__ ||= Hash.new{|h,k| h[k] = 0.0} end
   end

   module InstanceMethods
     def __delay_last__() self.class.__delay_last__ end
     def __delay_time__() self.class.__delay_time__ end
     def __delay_init__() extend Sync_m unless Sync_m === self end
     def __delay__ m
       m = m.to_s
       synchronize do
         last, now = __delay_last__[m], Time.now
         if last
           already = now.to_f - last.to_f
           t = __delay_time__[m] - already
           sleep t if t > 0
         end
         __delay_last__[m] = Time.now
         yield
       end
     end
   end

   def self.included other
     other.extend ClassMethods
     other.module_eval{ include InstanceMethods }
   end
end

class C
   include Delay

   def foo
     STDOUT.sync = true
     puts "#{ Thread.current.object_id } : #{ Time.now }"
   end

   delay 'foo', 2
end

c = C.new

t1 = Thread.new { 2.times{ c.foo } }
t2 = Thread.new { 2.times{ c.foo } }

t1.join
t2.join



harp:~ > ruby a.rb
-609340922 : Wed Jun 07 12:48:22 MDT 2006
-609341842 : Wed Jun 07 12:48:24 MDT 2006
-609340922 : Wed Jun 07 12:48:26 MDT 2006
-609341842 : Wed Jun 07 12:48:28 MDT 2006


regards.

-a
-- 
suffering increases your inner strength.  also, the wishing for suffering
makes the suffering disappear.
- h.h. the 14th dali lama