sleep_forever      87 thread.c       static void sleep_forever(rb_thread_t *th, int nodeadlock, int spurious_check);
sleep_forever     852 thread.c       	    sleep_forever(th, 1, 0);
sleep_forever    1143 thread.c           sleep_forever(GET_THREAD(), 0, 1);
sleep_forever    1150 thread.c           sleep_forever(GET_THREAD(), 1, 1);
sleep_forever     423 thread_sync.c      sleep_forever(GET_THREAD(), 1, 0); /* permit spurious check */