require "thread"

s = Semaphore.new(1)

t1 = Thread.new { s.down; Thread.stop; s.up }
t2 = Thread.new { s.down; puts "It works" }

puts t1.status
puts t1.backtrace
puts t2.status
puts t2.backtrace

t1.run

puts t1.status
puts t1.backtrace
puts t2.status
puts t2.backtrace