On Thu, Jun 22, 2023, at 5:02 AM, Andrew Tropin wrote: > On 2023-06-22 01:21, Philip McGrath wrote: >> >> In any case, the current documentation for >> atomic-box-compare-and-swap! is clear that the comparison is eq?: it >> just means that, when the behavior of eq? is unreliable, so is the >> behavior of atomic-box-compare-and-swap!. > > Good. Than implementation of atomic-box-update! looks correct to me. > Any thoughts on including it in (ice-9 atomic)? > >> >> Tangentially, does atomic-box-compare-and-swap! handle spurious >> failures on architectures like ARM, or does it expose machine >> semantics to the programmer? Maybe that's covered by details of the >> C11 memory model, but I don't think "sequential consistency" alone is >> enough to answer the question. >>
I think your implementation is correct. If atomic-box-compare-and-swap! does not handle spurious failures, I think your implementation is still correct, but a more efficient implementation could retry without an extra call to the update procedure. Someone with a better sense of Guile performance might have a view about whether `apply` is likely to be expensive: alternatively, the update procedure could be restricted to a single argument, or `case-lambda` could provide a specialized entry-point. -Philip
