Something is wrong with my threads

Would any of you smart folks like to tell me what stupid thing I am doing here?

At this point I have a test program that just uses plain MRI, no gems.  If I keep running it, it will eventually fail (after a dozen runs at most).  Code at the end of this post.

What I'm doing is creating a lot of identical threads.  In each one I stop immediately, and then after the thread is re-entered, set a thread variable to say the thread is done then stop again.  I run them all, and then check they are all done.

The problem is, sometimes they aren't all done.  Which makes no sense to me.  Either `thread#run` sometimes doesn't wake a thread, or doesn't pass control to the thread; or something is wrong with thread variables?

Code:

require "time"

def make_thread(idx)
  Thread.new do
    # Set things up and wait
    Thread.current[:idx] = idx
    Thread.stop

    # do the work, then say we're done
    Thread.current[:done] = true
    Thread.stop
  end
end


threads = []; 1.upto(200){|i| threads << make_thread(i) }
starttm = Time.now

# Do the work
threads.each{|t| t.run }

# Wait until all work is done or we time out
sleep 0.1 until (threads.all?{|t| t[:done] } || Time.now >= starttm + 10)

# If all work is not done, something has gone very wrong?
fails = threads.reject{|t| t[:done] }
if fails.size > 0
  puts "FAIL"
  fails.each{|e| puts "#{e[:idx]}: #{e.alive?}" }
end




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