gc-标记整理算法的两种实现

https://gentlezuo.github.io/2019/08/10/gc-%E6%A0%87%E8%AE%B0%E6%95%B4%E7%90%86%E7%AE%97%E6%B3%95%E7%9A%84%E4%B8%A4%E7%A7%8D%E5%AE%9E%E7%8E%B0/