> On 5 Dec 2016, at 1:53 AM, Andrew Trick <atr...@apple.com> wrote: > >> >> On Nov 30, 2016, at 5:40 AM, Anders Ha via swift-users >> <swift-users@swift.org <mailto:swift-users@swift.org>> wrote: >> >> Hi guys >> >> I have recently started adopting lock-free atomics with memory fences, but >> it seems Swift at this moment does not have any native instruments. >> >> Then I read a thread in the Apple Developer Forum >> (https://forums.developer.apple.com/thread/49334 >> <https://forums.developer.apple.com/thread/49334>), which an Apple staff >> claimed that all imported atomic operations are "not guaranteed to be >> atomic". But for my tests with all optimizations enabled (-Owholemodule and >> -O), the OSAtomic primitives and stdatomic fences do not seem going wild. >> >> Is these `atomic_*` and `OSAtomic*` primitives really unsafe in Swift as >> claimed? It doesn't seem like the Swift compiler would reorder memory >> accesses around a C function call that it wouldn't be able to see through. > > Did you get an answer to this? I’m not sure what led you to believe the > primitives are unsafe in Swift. Importing them doesn’t change their semantics. > > -Andy
I wrote to ask because I have stumbled on the posts (which I linked) of a colleague of yours working on Core Audio, with the specific quote of "even using functions imported from C is not guaranteed to be atomic". To some extent I believe it is true, since the Swift compiler does not define a memory model to say it doesn't reorder stuff in this or that situation. But it doesn't seem to be a problem in practice, as stuff apparently isn't being reordered around the function calls in generated code. So I guess the answer is "Swift does not have a memory model and you are relying on a unconstrained aspects of the compiler not to fail you". Hmm? Regards, Anders > >> P.S. Is any of these primitives available on Linux? It seems the glibc >> modulemap does not export an `stdatomic` submodule at all. >> >> Best Regards, >> Anders >> >> _______________________________________________ >> swift-users mailing list >> swift-users@swift.org <mailto:swift-users@swift.org> >> https://lists.swift.org/mailman/listinfo/swift-users >> <https://lists.swift.org/mailman/listinfo/swift-users>
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