sema_init (&sema[0], 0, "ping");
sema_init (&sema[1], 0, "pong");
thread = thread_create ("sema-test", sema_test_helper, &sema);
sema_init (&sema[0], 0, "ping");
sema_init (&sema[1], 0, "pong");
thread = thread_create ("sema-test", sema_test_helper, &sema);