C++ What atomic operations we can use on trival user defined data type

Question

I am trying to understand std::atomic types and atomic operations. Below is my code:

#include <atomic>
#include <iostream>

class A
{
public:
    int x;
    void Show() {}
};

int main()
{
    std::atomic<A> fooA;
    // fooA.Show(); -- gives me std::atomic<A> has no member Show()
}

What are the atomic operations we can do when we define a user type - like Mtype.load() etc - how can we use Mtype with load() atomic operations - where load atomically obtains the value of the atomic object?

You cannot call the member functions directly on the atomic. You have to first get the value. You have to use either `std::atomic_load` or a member function `load`. See [docs](https://en.cppreference.com/w/cpp/atomic/atomic) — Croolman, Sep 01 '20 at 06:40

score 0 · Accepted Answer · answered Sep 02 '20 at 19:13

An atomic operation only makes sense whereby you can perform a compare-and-swap exchange on the given data type. This means the data must be "trivially copyable".

For anything bigger than an integral type, you're better off using a mutex to protect the elements of a structure which are accessible from multiple threads - "shared mutable state".

For more information see this post: How to use std::atomic<> effectively for non-primitive types?

C++ What atomic operations we can use on trival user defined data type

1 Answers1