barrier:
	return record of
		count := 0
		mutex := semaphore(1)
		turnstile1 := semaphore(0)
		turnstile2 := semaphore(1)

wait(barrier):
	barrier_phase1(barrier)
	barrier_phase2(barrier)

barrier_phase1(barrier):
	wait(mutex)
	if ++count == thread_count then
		wait(turnstile2)
		signal(turnstile1)
	signal(mutex)

	wait(turnstile1)
	signal(turnstile1)

barrier_phase2(barrier):
	wait(mutex)
	if --count == 0 then
		wait(turnstile1)
		signal(turnstile2)
	signal(mutex)

	wait(turnstile2)
	signal(turnstile2)

main:
	shared thread_count := read_integer()
	shared my_barrier := barrier(thread_count)
	create_thread(secondary, thread_count)

secondary:
	while true do
		Sentence A
		barrier_phase1(my_barrier)
		Sentence B
		barrier_phase2(my_barrier)

third:
	for row := 0 to row_count do
		process_row()
		wait(mybarrier)