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【面試】詳解同步/異步/阻塞/非阻塞/IO含義與案例

時間：2021-07-12 18:13:04 阅读：0 評論：0 收藏：0 [點我收藏+]

標簽：用戶線程 src href 代碼 bat people 同步數據拷貝

本文詳解同步、異步、阻塞、非阻塞，以及IO與這四者的關聯，畢竟我當初剛認識這幾個名詞的時候也是一臉懵。

??1.同步阻塞、同步非阻塞、異步阻塞、異步非阻塞
??2.IO與上述四者的關聯

??1.同步阻塞、同步非阻塞、異步阻塞、異步非阻塞

1.同步

同步就是多個事物不能同時工作，只能依次排隊進行

2.異步

多個事物可以同時工作，不用依次進行

3.阻塞

線程需要停止等待

4.非阻塞

線程可以運行工作

5.四者關聯

同步/異步，關注的是能不能同時工作

阻塞/非阻塞，關注的是能不能動

同步阻塞：不能同時工作，也不能動。比如只有一條小道，一次只能過一輛車，可悲的是都堵上了。
同步非阻塞，不能同時開工，但可以動。比如只有一條小道，一次只能過一輛車，幸運的是可以正常通行。
異步阻塞，可以同時開工，但不可以動。有多條路，每條路都可以跑車，可氣的是全都堵上了。
異步非阻塞，可以工時開工，也可以動。有多條路，每條路都可以跑車，很爽的是全都可以正常通行。

回到程序中對應線程就是

同步阻塞，相當于一個線程在等待。
同步非阻塞，相當于一個線程在正常運行。
異步阻塞，相當于多個線程都在等待。
異步非阻塞，相當于多個線程都在正常運行。

??2.IO與上述四者的關聯

1.IO、阻塞IO、非阻塞IO

IO: 指的就是读入/写出數據的过程，和等待读入/写出數據的过程。一旦拿到數據后就变成了數據操作了，就不是IO了
- 阻塞IO：用戶線程被阻塞在等待數據上或拷貝數據上
- 非阻塞IO：用戶線程没有因为IO的事情出现阻塞

2.同步IO、同步阻塞IO

在IO中，同步与非阻塞是互斥的，即不存在同步非阻塞IO，而同步非阻塞即存在的，但那不叫IO，叫操作數據

同步IO：必须拿到IO的數據，才可以继续执行。对应代碼中读取文件然后操作
非阻塞IO：发起IO请求后，代碼就可以往下执行。即一定不是同步。

所以，同步IO一定是阻塞IO，同步IO等于同步阻塞IO。且不存在同步非阻塞IO

3.異步IO、異步阻塞IO、異步非阻塞IO

异步IO：异步IO是指发起IO请求后，不用拿到IO的數據就可以继续执行
- 异步阻塞IO：发起IO请求后，在拷貝數據这个过程中，线程发生了阻塞。
- 异步非阻塞IO：发起IO请求后，收到通知，數據处理好了，且这个过程没发生阻塞。

【面試】詳解同步/異步/阻塞/非阻塞/IO含義與案例

標簽：用戶線程 src href 代碼 bat people 同步數據拷貝

原文地址：https://www.cnblogs.com/meditation5201314/p/14999000.html

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