为什么libc ++的shared_ptr实现使用完整的内存屏障而不是宽松的内存? [英] Why does libc++'s implementation of shared_ptr use full memory barriers instead of relaxed?

问题描述

在 shared_ptr 的boost实现中，它使用

In boost's implementation of shared_ptr, it uses relaxed memory ordering to increment its reference count. This appears safe as decrements use acquire/release to make sure that any previous decrements are visible to the thread before releasing memory. This method seems correct and appears in Herb Sutters talk on atomics

在libc ++的实现中，使用完整的内存屏障

In libc++'s implementation uses full memory barriers

template <class T>
inline T
increment(T& t) _NOEXCEPT
{
    return __sync_add_and_fetch(&t, 1);
}

template <class T>
inline T
decrement(T& t) _NOEXCEPT
{
    return __sync_add_and_fetch(&t, -1);
}

}  // name

有此决定的原因吗?两者之间在性能或安全性方面有区别吗?

Is there a reason for this decision? Are there any performance or safety differences between them?

推荐答案

由于我编写该代码时，编译器(clang)尚未实现C ++ 11原子.而且我从来没有回过头来清理它.

Because when I wrote that code, the compiler (clang) had not yet implemented C++11 atomics. And I never got back to it to clean it up.

这里没有什么微妙的地方.:-)

Nothing subtle here. :-)

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