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关于同步非阻塞 IO 增加一点说明 #2694

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3 changes: 3 additions & 0 deletions docs/java/io/io-model.md
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Expand Up @@ -87,6 +87,9 @@ Java 中的 NIO 可以看作是 **I/O 多路复用模型**。也有很多人认

相比于同步阻塞 IO 模型，同步非阻塞 IO 模型确实有了很大改进。通过轮询操作，避免了一直阻塞。

> 同步非阻塞 IO，发起一个 read 调用，如果数据没有准备好，这个时候应用程序可以不阻塞等待，而是切换去做一些小的计算任务，然后很快回来继续发起 read 调用，也就是轮询。这个
> 轮询不是持续不断发起的，会有间隙, 这个间隙的利用就是同步非阻塞 IO 比同步阻塞 IO 高效的地方。

但是，这种 IO 模型同样存在问题：**应用程序不断进行 I/O 系统调用轮询数据是否已经准备好的过程是十分消耗 CPU 资源的。**

这个时候，**I/O 多路复用模型** 就上场了。
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