4 ms·

According to a comment in the blog post, the sementic had changed in C++20: > If your compiler predates C++20, however, the consume memory order is almost cert

According to a comment in the blog post, the sementic had changed in C++20: > If your compiler predates C++20, however, the consume memory order is almost certainly treated as acquire (legal, just not faster). C++17 temporarily discouraged the use of the consume order because the semantics were impossible to use correctly, and thus all compilers were implementing it as acquire. > > The revisions in C++20 took some very smart people a lot of effort, and changed the definitions subtly so that you can use consume and get weaker memory ordering than acquire without immediately invoking our good friend UB.

tialaramex 3y ago
That is what the comment says, but, it doesn't seem to match reality. "To verify comments I saw on Raymond Chen's blog" isn't enough justification for me to pay ISO's fees for the actual ISO C++ 20 standard document, but the draft the committee members work from still says of Consume: > Implementations have found it infeasible to provide performance better than that of memory_order :: acquire. I suspect that the comment is well-meant but is referring to some proposal that may have been made at some point in the last say five years, and which isn't in the ISO standard. Plenty of people have proposed that Consume could be fixed, but there are big gaps between proposing a fix, agreeing it among all interested parties and writing that fix into the standard, and actually shipping compilers with working Consume memory order.