Re: Atomic caching of smart pointers

Am 16.09.2024 um 08:01 schrieb Paavo Helde:

On 15.09.2024 23:15, Chris M. Thomasson wrote:

On 9/15/2024 11:54 AM, Paavo Helde wrote:
[...]

So, what do you think? Should I just use std::atomic<std::shared_ptr> instead? Any other suggestions? Did I get the memory order parameters right in compare_exchange_weak()?

>
Keep in mind that you need to make sure that std::atomic<std::shared_ptr> is actually lock-free...
>
Make sure to investigate is_always_lock_free on your various arch's:
>
https://en.cppreference.com/w/cpp/atomic/atomic/is_always_lock_free

 I already checked this, it is returning false at least on one of my target platforms (Visual Studio 2022, Windows x86_64). IIRC Bonita claimed this might be a false negative though.

Yes, no implementation of atomic<shared_ptr<>> of MSVC, libstdc++ and
libc++ is currently lock-free. And even if: it needs the shortcut-opti-
mization which checks if a central atomic<shared_ptr<>> is unchanged
against a shared_ptr<>. With that even a futex'd solution woul  be fast
enough for RCU-like patterns, i.e. when the atomic<shared_ptr<>> is
rarely updated.