April 2018
Intermediate to advanced
303 pages
4h 54m
Chinese
Content preview from Effective Modern C++（中文版）
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228
第
7
章
并发
API
C++11
的至伟功勋之一，就是将并发融入了语言和库中。熟悉其他线程
API
（例如，
pthread
或
Windows
线程库）的程序员有时会对
C++
提供的相对斯巴达式地简练的特
性集感觉惊讶，但这是因为，
C++
对并发的支持中有一大部分是以对编译器厂商实施
约束的形式提供的。由此得到的一系列语言层面的保障，意味着在
C++
的历史上，程
序员首次可以跨越所有平台撰写具有标准行为的多线程程序。这就为建立富有表达力
的库奠定了坚实的基础，而标准库中的并发元素（任务、期值、线程、互斥量、条件
变量和原子对象等）仅仅是个开端，今后在开发并行
C++
软件时，肯定会有一套越来
越丰富的工具集。
在本章随后的条款中请牢记，标准库中为期值准备了两个模板：
std::future
和
std::shared_future
。在很多情况下，它们之间的区别并不重要，所以我经常仅仅谈
论期值概念，意思是指可以对这两种都适用。
条款
35
：优先选用基于任务而非基于线程的程序
设计
如果你想以异步方式运行函数
doAsyncWork
，有两种基本选择。你可以创建一个
std::thread
，并在其上运行
doAsyncWork
，因此这是基于线程（
thread-based
）的途径：
int doAsyncWork();
std::thread
t(doAsyncWork);
抑或，你可以把
doAsynWork
传递给
std::async
，这种策略叫做基于任务（
task-based
）：
并发
API
｜
229
auto fut =
std::async ...
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