[PATCH] Want feedback for potential implementation of P2643R2 atomic features

[Teodor Spæren]

Hello!

Earlier I sent an email about wanting to try to implement the new 
features described in 
https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2024/p2643r2.html

I've now gone and done that. I've added the support for all the commands 
for floats, and integer values, as well as atomic_flag. I've added tests 
for atomic_integer. I will of course finish all the types and add tests 
for all the types, but I wanted to know if this is work that is wanted 
or if it's to early to implement, and I also wanted some feedback.

I have a couple of questions:

1. How should I feature test for this to be enabled or not? For the 
`wait` and `notify` functionality #if __glibcxx_atomic_wait is used,
should I guard this behind a new type of flag?


2. How is the formatting? Is there a command to format all the files?


3. What timeout values should I use for tests? I don't want the waiting 
to take 2seconds, but I also don't want the tests to fail 
intermittently. I've tried to use 60ms buffer now, but this seems like a 
lot to me.

4. Why does "__atomic_wait_address_for_v" take the "old" parameter by 
rvalue reference? Immediately we call a function which takes the 
parameter by value. Is this just an oversight or is there some semantics 
here that I'm not aware of?


I've attached the patches in what I hope is a good format, I hope that 
I've not butchered this completely!

Best regards,
Teodor Spæren
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