update docs and tests for weak cas! and lock! operations
#731
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burgerrg
requested changes
Oct 18, 2023
The `vector-cas!`, `box-cas!`, and `ftype-lock!` operations are "weak" in the sense that they may spuriously fail on an architecture (like AArch64) with a weak memory model. Also, they do not necessarily imply any overall memory ordering, so using `memory-order-acquire` and `memory-order-release` may be needed. The documentation did not make this clear, and some tests did not handle spurious failure. Closes cisco#720
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One of the tests triggered the error near line 1176 of mats/misc.ms. The call |
Thanks - I'll work on that in another PR in the near future, since it's unrelated to the change here. |
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Thank you for this helpful update! |
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This PR is intended to close #720.
The
vector-cas!,box-cas!, andftype-lock!operations are "weak" in the sense that they may spuriously fail on an architecture (like AArch64) with a weak memory model. Also, those operation do not necessarily imply any overall memory ordering, so usingmemory-order-acquireandmemory-order-releasemay be needed. The documentation did not make this clear, and some tests did not handle spurious failure.As noted in the discussion for #720, a good case could be made that these operations should be "strong", which could mean both avoiding spurious failure and ensuring more memory ordering. The approach here is conservative: it keeps the current implementation and allows access to the underlying machine's behavior, but it's also compatible with the possibility that we decide to strengthen guarantees in the future.