> For the complete documentation index, see [llms.txt](https://book.bsdcn.org/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://book.bsdcn.org/4.3-bsd-unix-cao-zuo-xi-tong-she-ji-yu-shi-xian/di-si-bu-fen-jin-cheng-jian-tong-xin/10.2.-shi-xian-jie-gou-yu-gai-shu.md).

# 10.2 实现结构与概述

如图 10.2 所示，进程间通信设施分层叠加在网络设施之上。数据从应用经套接字层流向网络支持，反之亦然。套接字层所需的状态完全封装在套接字层内，而协议相关的状态维护在支撑协议专有的辅助数据结构中。传输数据所用存储的责任由套接字层移交网络层；始终如一地遵守这条规则有助于简化存储管理的细节。套接字层内，套接字数据结构是一切活动的焦点。系统调用接口例程管理与一次 UNIX 系统调用相关的动作，收集系统调用参数（见 3.2 节），把用户数据转换成第二级例程期望的格式。套接字抽象的大部分在第二级例程中实现。所有第二级例程的名字都带 `so` 前缀，直接操纵套接字数据结构并管理异步活动之间的同步；这些例程列于表 10.1。

![图 10.2 进程间通信实现的分层](https://1991889543-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FilVST9xTgD47M0g8ham7%2Fuploads%2Fgit-blob-f8649a862ea8d80bdbecfc286fb17b0e65fcc157%2Ffig-10-2-figure-10-2-interprocess.png?alt=media)

表 10.1 套接字层支持例程

| 例程             | 功能            |
| -------------- | ------------- |
| `socreate()`   | 创建新套接字        |
| `sobind()`     | 把名字绑定到套接字     |
| `solisten()`   | 把套接字标记为监听连接请求 |
| `soaccept()`   | 接受套接字上的未决连接   |
| `soconnect()`  | 发起到另一套接字的连接   |
| `soconnect2()` | 在两个套接字之间创建连接  |
| `sosend()`     | 发送数据          |
| `soreceive()`  | 接收数据          |
| `soshutdown()` | 关闭数据发送或接收     |
| `sosetopt()`   | 设置套接字选项的值     |
| `sogetopt()`   | 读取套接字选项的值     |

本章余下部分集中于套接字层的实现。10.3 节讨论套接字层及以下网络子系统的内存管理；10.4 节讲套接字及相关数据结构；10.5 节给出连接建立的算法；10.6 节讨论数据传输；10.7 节描述连接关闭。本章中提到网络通信协议提供的支撑设施时一带而过，不作展开；网络协议与套接字层交互的完整描述见第 11 章，网络协议的内部在第 12 章呈现。


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