All atomic exchanges with _Api_level should be acq_rel

[AZero13]

As _Api_level is not always accessed with sequential ordering, and _Level is thread-local, acq_rel is good enough for all compare_exchange successes. However, this means we need to explicitly mention acquire for the failure case.

[AZero13]

@CaseyCarter Fixed!

[frederick-vs-ja]

Hmm... I wonder what happened to your environment. Is there anything enforcing to force-push a single commit?

[StephanTLavavej]

Thanks, this is a good change, and is consistent with the very similar code in tzdb.cpp:

STL/stl/src/tzdb.cpp

Lines 57 to 58 in 87580ca

	while (!_Icu_functions._Api_level.compare_exchange_weak(
	_Level, _Icu_api_level::_Detecting, _STD memory_order_acq_rel)) {

I'd still like to understand why you keep force-pushing and ignoring our requests to avoid doing so, but that shouldn't block merging this change. At least GitHub started providing a "Compare" button, although it's still harder to see what's changed over time than with the ordinary commits that everyone else uses.

[StephanTLavavej]

I'm mirroring this to the MSVC-internal repo - please notify me if any further changes are pushed.

[StephanTLavavej]

Thanks for improving the consistency of these atomic operations by avoiding full sequential consistency! 😹 ☢️ 🎉