Thread

1. wahern · 1789747013 · focus · HN ↗

   > When both conditions are met, the loop body is replaced with a call to std::this_thread::yield(). This gives execution of the loop the forward-progress semantics it previously lacked.

   That's the epitome of the hidden code downside that Linus and many others dislike about C++. For constructors and destructors it's somewhat unavoidable and not so random, though Rust does better at limiting the blast radius of non-local code, at least in the drop case.

   If they didn't want to adopt the C11 rule, the C++ committee should've explored a rule that required the compiler to emit a diagnostic or error for trivial loops (whether as defined by C11 or otherwise), requiring the programmer to explicitly insert ::yield or similar. No hidden code, and less opportunity for the compiler to do surprising things.

   The C committee has been rigorously enumerating UB cases in the standard and addressing each case in turn, often by requiring a diagnostic, error, or by turning it into implemention defined behavior. But inserting code like that would be unthinkable.

   1. IsTom · 1789747710 · focus · HN ↗

      > should've explored a rule that required the compiler to emit a diagnostic or error for trivial loops (whether as defined by C11 or otherwise), requiring the programmer to explicitly insert ::yield or similar

      It wouldn't work when this kind of loop is generated by macros/templates in some unreachable case left after const folding.

      1. rcxdude · 1789748275 · focus · HN ↗

         If it's truly unreachable then it's not likely to be a problem. If it is reachable and it's emerging from some macros and templates then I would be more inclined want a warning for it.

         1. IsTom · 1789748683 · focus · HN ↗

            Yeah, but then you need compiler to somehow know if it's truly unreachable to know when to emit the warning and when to not do that.

            1. krupan · 1789751797 · focus · HN ↗

               If it's a warning and not an error then emit it whether it's unreachable or not

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