c++ - 为什么没有数据竞赛？

Question

我正在 Memory Model 上阅读 Bjarne 的常见问题解答, 这是一段话

So, C++11 guarantees that no such problems occur for "separate memory locations.'' More precisely: A memory location cannot be safely accessed by two threads without some form of locking unless they are both read accesses. Note that different bitfields within a single word are not separate memory locations, so don't share structs with bitfields among threads without some form of locking. Apart from that caveat, the C++ memory model is simply "as everyone would expect.''

However, it is not always easy to think straight about low-level concurrency issues. Consider:

start with x==0 and y==0

if (x) y = 1; // Thread 1

if (y) x = 1; // Thread 2

Is there a problem here? More precisely, is there a data race? (No there isn't).

我的问题是，为什么没有数据竞争？对我来说很明显，显然存在数据竞争，因为线程 1 是 y 的编写器，而线程 2 是 y 的读取器，同样是 x 。

Answer 1

x 和 y 是 0 因此 if 后面的代码将不会被执行没有写入，因此不会有数据竞争。