写入数组中的不同偏移量总是定义良好 [英] Writing to different offsets in array always well defined

问题描述

在这个问题中，有人提出同时在char数组中写入两个不同的偏移量将意味着数据竞争. ，由于某些处理器(例如Alpha)没有按字节寻址，因此很难实现这一点.

In this question it was brought up that writing to two different offsets in a char array concurrently would imply a data race, since some processors such as Alpha don't have byte-wise addressing so it'd be hard to implement this.

我当然知道这会大大减慢在alpha处理器上写入字节的速度(基本上涉及LL/SC)，但是据我了解C ++标准，数组中的每个字段都是其自己的内存位置(尽管从§1.7读取) ，我还可以将整个数组视为一个内存位置-这可能就是这个问题的原因.

I certainly see that this would very much slow down writing bytes on alpha processors (basically involving a LL/SC), but as I understand the C++ standard every field in an array is its own memory location (although from reading §1.7, I could also see the whole array as one memory location - that's probably what this question boils down to).

下面的伪代码基本上是

char arr[10]; // global field
Thread 1:
arr[1] = 0;
Thread 2:
arr[0] = 1;

定义是否符合C ++ 14标准?

well defined according to the C++14 standard or not?

推荐答案

根据C ++ 14标准(1.7/3):

From the C++14 standard (1.7/3):

两个或多个执行线程(1.10)可以更新和访问单独的内存位置，而不会互相干扰.

Two or more threads of execution (1.10) can update and access separate memory locations without interfering with each other.

先前定义的位置(强调我的位置)

Where it previously defines (emphasis mine)

存储位置可以是标量类型的对象，也可以是相邻位字段的最大序列，所有这些位都具有 非零宽度.

A memory location is either an object of scalar type or a maximal sequence of adjacent bit-fields all having non-zero width.

因此数组的char是内存位置，但是数组本身不是；因此，写入不同char的单独线程不会互相干扰.

So the chars of the array are memory locations, but the array itself is not; therefore, separate threads writing to different chars do not interfere with each other.

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