What about `withUnsafeMutablePointer` on a stored object property, marked with `final`? e.g. `withUnsafeMutablePointer(to: &object.lock, os_unfair_lock_lock)`.
The generated object code with `-Owmo` shows that it is optimised to an address calculation immediately followed by a call to `os_unfair_lock_lock`. But I am not quite sure about its behaviour with no optimisation flag. Regards, Anders > On 6 Dec 2016, at 1:27 AM, Joe Groff <jgr...@apple.com> wrote: > >> >> On Dec 4, 2016, at 4:53 PM, Andrew Trick via swift-users >> <swift-users@swift.org <mailto:swift-users@swift.org>> 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. > > If you apply them to memory you allocated manually with malloc/free on > UnsafeMutablePointer's allocation methods, then yeah, they should work as > they do in C. That's the safest way to use these functions today. Passing a > Swift `var` inout to one of these functions does not guarantee that accesses > to that var will maintain atomicity, since there may be bridging or > reabstracting conversions happening under the hood. > > -Joe
_______________________________________________ swift-users mailing list swift-users@swift.org https://lists.swift.org/mailman/listinfo/swift-users
