From: Jake McArthur <jake.mcarthur@...>
Date: 2006-07-19T04:54:55+09:00
Subject: Re: [QUIZ][SOLUTION] Negative Sleep (#87)

--Apple-Mail-1-999253821
Content-Transfer-Encoding: 7bit
Content-Type: text/plain;
	charset=US-ASCII;
	delsp=yes;
	format=flowed

I took the concept of negative sleeping as guaranteeing that the  
thread will not sleep or relinquish control for that time period.  
Normal sleep means that the thread concedes to the other threads of  
the program for the specified time, so negative sleeping is forcing  
all other threads to concede control to the current thread for the  
specified time instead. That said, here is my code:

module Kernel
   alias normal_sleep sleep
   def sleep(seconds)
     normal_sleep(seconds) and return if seconds >= 0
     priorities = {}
     (Thread.list - [Thread.current]).each do |thread|
       priorities[thread] = thread.priority
       thread.priority = Thread.current.priority-1
     end
     Thread.new do
       normal_sleep(-seconds)
       priorities.each do |thread, priority|
         thread.priority = priority
       end
     end
   end
end

This is difficult to test cleanly since positive sleeping within the  
current thread gives the de-prioritized threads a chance to run for a  
short time (though I do see that as appropriate behavior... a thread  
that is negative sleeping should still be able to positive sleep for  
a short time). It is testable if you are willing to read extremely  
long outputs or are willing to put up with using some long, empty  
loops to minimize output.

  - Jake McArthur
--Apple-Mail-1-999253821--