shared a1_ready := semaphore(0)
shared b1_ready := semaphore(0)

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

thread_a:
  statement a1
  wait(b1_ready);
  signal(a1_ready);
  statement a2

thread_b:
  statement b1
  signal(b1_ready);
  wait(a1_ready);
  statement b2