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c++c++11stdstdatomic

Is atomic<T*> always lock free?

On my MAC OS, atomic<T*> is lock free.

#include <iostream>
#include <atomic>

int main() {
    std::cout << std::atomic<void*>().is_lock_free() << std::endl;
    return 0;
}

output: 1

I want to know if atomic<T*> is always lock free?

Is there a reference to introduce it?

Solution

  • The standard allows implementing any atomic type (with exception of std::atomic_flag) to be implemented with locks. Even if the platform would allow lock-free atomics for some type, the standard library developers might not have implemented that.

    If you need to implement something differently when locks are used, this can be checked at compile time using ATOMIC_POINTER_LOCK_FREE macro.