Easy to reason about linear overlapped execution of multiple threads to force contention for tests.

linear_contention.rb

require "thread"

# Easy to reason about linear overlapped execution of multiple threads to
# force contention for tests.
#
#                           -------- Time ------->
# Thread.current    1 ---------------------------------- 4
# t2                             2 ------- 3

m = Mutex.new
cv = ConditionVariable.new

m.synchronize do
  puts "1."

  t2 = Thread.new do
    m.synchronize do
      puts "2."
      cv.signal
      puts "3."
    end
  end

  cv.wait(m)
  puts "4."
end