Add a "relaxed" memory order - #8984
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The memory order is not the C++ relaxed memory order, but rather the slightly stronger load-store ordered memory order, which prevents out-of-thin-air values by forbidding earlier atomic loads from being reordered past later atomic stores. This makes it impossible to construct the self-justifying causality cycle that gives rise to out-of-thin-air values. The name of the memory order in both the implementation and the text format is likely to change in the future to become more descriptive.
| } | ||
| // Shared location accesses cannot be reordered after (but may be able to be | ||
| // reordered before) release stores. | ||
| if (other.writeOrder >= MemoryOrder::AcqRel && |
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Looks like this was a bug before the MemoryOrder enum ordering changed in this PR? Ditto for line 381. Currently before this PR AcqRel > SeqCst.
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Yeah, thankfully I think the bug was harmless because we fell through to the explicit handling of MemoryOrder::SeqCst below, which still gave us the correct behavior.
stevenfontanella
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Looks like the atomics.js test fails on the emscripten CI, is that related to this change? And second, do we plan to add this to the fuzzer and C + JS APIs in a future PR?
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Yeah, this PR had attempted to add support to the JS API, but 1) the syntax was wrong and 2) support was missing in the C API. Both are fixed in the last commit. |
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The memory order is not the C++ relaxed memory order, but rather the slightly stronger load-store ordered memory order, which prevents out-of-thin-air values by forbidding earlier atomic loads from being reordered past later atomic stores. This makes it impossible to construct the self-justifying causality cycle that gives rise to out-of-thin-air values. The name of the memory order in both the implementation and the text format is likely to change in the future to become more descriptive.