void os::yield_all(int attempts) {

  {- -------------------------------------------
  (1) sched_yield() を呼び出すだけ.

      (<= スレッドが SCHED_OTHER なんだが, この場合も sched_yield() でいいんだっけ?? 要確認 #TODO)
      ---------------------------------------- -}

      // Yields to all threads, including threads with lower priorities
      // Threads on Linux are all with same priority. The Solaris style
      // os::yield_all() with nanosleep(1ms) is not necessary.
      sched_yield();
    }