shared can_a_continue := semaphore(0)
shared can_b_continue := semaphore(0)

main:
  create_thread(thread_a, 1)
  create_thread(thread_b, 1)

thread_a:
  statement a1
  signal(can_b_continue);
  wait(can_a_continue);
  statement a2

thread_b:
  statement b1
  signal(can_a_continue);
  wait(can_b_continue);
  statement b2