gistfile1.builder

require 'thread'

m = Mutex.new
m.lock
wt2 = Thread.new do
   m.lock
   sleep 2
   m.unlock
end

# Ensure wt2 is waiting on m
sleep 0.1

wt1 = Thread.new do 
   m.lock
   m.unlock
end
# Ensure wt1 is waiting on m
sleep 0.1

# Give it to wt2

m.unlock

wt1.join