C ++中的内存模型：顺序一致性和原子性 [英] Memory Model in C++ : sequential consistency and atomicity

问题描述

我有一些问题与C ++ 11中的内存模型有关。

在 https://www.think-cell.com/en/career/talks/pdf/think-cell_talk_memorymodel.pdf 29.幻灯片是写的

C ++内存模型保证顺序一致性

但是，在我以前的帖子中，我了解到C ++内存具有弱内存模型 - 编译器可以按需要重新排序 - 他必须满足 规则。 p>

解决方案

我想通过阅读早期的幻灯片，我想出了这张幻灯片正在谈论的内容：

幻灯片12：
顺序一致性[Leslie Lamport，1979]

任何执行的结果是相同的as-if

1. 所有主题的操作都以
   顺序执行

slide14：
无数据竞争程序的顺序一致性

SC -DRF：

• 我们注意我们的计划不包含数据竞赛


• 系统保证顺序一致的执行

在幻灯片29上，作者们说一旦你使用 std :: atomic 避免数据族UB，程序就会以程序顺序运行。

这是一个有趣的方式来看看C ++的弱内存模型。

第二部分
$ b

请不要一次性提出两个完全不同的问题。

这个CPU怎么做？问题将更适合作为您稍后问题的一部分： x86上的Atomicity

我已经写了大部分的答案，我会把它放在那里。

I have some questions connected with memory model in C++11.

On https://www.think-cell.com/en/career/talks/pdf/think-cell_talk_memorymodel.pdf on the 29. slide is written

The C++ memory model guarantees sequential consistency

But, in my previous posts I learnt that C++ memory has weak memory model- the compiler can make reorder as he wants- he has to satisfy as if rule.

解决方案

I think I figured out what that slide is talking about, from reading the earlier slides:

slide 12: sequential consistency [Leslie Lamport, 1979]
the result of any execution is the same as-if

1. the operations of all threads are executed in some sequential order
2. the operations of each thread appear in this sequence in the order specified by their program

slide14: sequential consistency for data-race-free programs
SC-DRF:

• We take care our program does not contain data races
• The system guarantees sequentially consistent execution

So on slide 29, the authors are saying that once you avoid data-race UB using std::atomic, the program runs as-if everything happened in program order.

This is an interesting way to look at C++'s weak memory model. This looks like a good set of slides.

---

Part two

Please don't make a habit of asking two very different questions at once.

This "how does the CPU do it?" question would be a better fit as part of your later question: Atomicity on x86

I have most of an answer to it already written, which I'll put there instead.

这篇关于C ++中的内存模型：顺序一致性和原子性的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！