April 2018
Intermediate to advanced
303 pages
4h 54m
Chinese
Content preview from Effective Modern C++（中文版）
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236
｜
第
7
章
在
C++14
中，对
reallyAsync
返回值进行推导型别的能力使函数声明得以简化：
template<typename F, typename... Ts>
inline
auto
// C++14
reallyAsync(F&& f, Ts&&... params)
{
return std::async(std::launch::async,
std::forward<F>(f),
std::forward<Ts>(params)...);
}
这一版本清清楚楚地显示，
reallyAsync
所做的一切，就是以
std::launch::async
启
动策略来调用了
std::async
。
要点速记
•
std::async
的默认启动策略既允许任务以异步方式执行，也允许任务以同
步方式执行。
•
如此的弹性会导致使用
thread_local
变量时的不确定性，隐含着任务可能
永远不会执行，还会影响运用了基于超时的
wait
调用的程序逻辑。
•
如果异步是必要的，则指定
std::launch::async
。
条款
37
：使
std::thread
型别对象在所有路径皆
不可联结
每个
std::thread
型别对象皆处于两种状态之一：可联结或不可联结。可联结的
std::thread
对应底层以异步方式已运行或可运行的线程。
std::thread
型别对象对应
的底层线程若处于阻塞或等待调度，则它可联结。
std::thread
型别对象对应的底层线 ...
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I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.