c++

std::atomic

看到有人讨论atomic是不是lockfree的

取决于硬件指令
The C++ standard recommends (but does not require) that lock-free atomic operations are also address-free, that is, suitable for communication between processes using shared memory.
https://en.cppreference.com/w/cpp/atomic/atomic_is_lock_free

测试实现

#include <iostream>
#include <utility>
#include <atomic>
#include <memory>
 
struct A { int a[4]; };
struct B { int x, y; };
struct C { std::shared_ptr<int> p; };
struct D { int a[5]; };

int main()
{
    std::atomic<A> a;
    std::atomic<B> b;
    std::atomic<C> c;
    std::atomic<D> d;
    std::cout << std::boolalpha
              << "std::atomic<A> is lock free? "
              << std::atomic_is_lock_free(&a) << '\n'
              << "std::atomic<B> is lock free? "
              << std::atomic_is_lock_free(&b) << '\n'
              << "std::atomic<C> is lock free? "
              << std::atomic_is_lock_free(&c) << '\n'
              << "std::atomic<D> is lock free? "
              << std::atomic_is_lock_free(&d) << '\n';
}

g++ a.cpp -std=gnu++11 -latomic

std::atomic<A> is lock free? true
std::atomic<B> is lock free? true
std::atomic<C> is lock free? true
std::atomic<D> is lock free? false