From: James Gray <james@...>
Date: 2009-02-11T07:58:30+09:00
Subject: Re: GC and Threads

On Feb 10, 2009, at 4:51 PM, James Gray wrote:

> I'm trying to prove two simple facts about how Ruby works:
>
> * Ruby can GC a Thread that has run to completion if you no longer  
> have any references to it, even if the value() have never been  
> collected
> * Ruby cannot GC a running Thread, even if there are no references  
> to it

> Simple scripts I've written seems to indicate they are accurate…

Actually, this is difficult to judge.  For example, this script has  
odd results on my machine.  The Thread count does drop, but not all  
the way:

#!/usr/bin/env ruby -wKU

def show_thread_count
   count = 0
   ObjectSpace.each_object(Thread) { |obj| count += 1 }
   p count
end

show_thread_count

5.times do
   Thread.new do
     date = `sleep 1 && date`
   end
end

20.times do
   sleep 0.2

   3.times { GC.start }
   show_thread_count
end

__END__

Here's a pretty typical output, though it varies a little:

$ ruby testing_thread_gc.rb
1
6
6
6
6
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3

Thoughts?

James Edward Gray II