Or allocate a pointer for it. The other alternative would be NSLock but that might be swatting flies with sledgehammers. We had a similar issue implementing NSLock in swift-corelibs-foundation where taking the address of a pthread mutex corrupted the structure for when another thread would attempt to grab it.
Sent from my iPhone > On Oct 12, 2016, at 4:45 PM, Shawn Erickson <[email protected]> wrote: > > So we would have to drop down to C code, etc. to safely leverage OSAtomic? > >> On Wed, Oct 12, 2016 at 8:32 AM Philippe Hausler via swift-users >> <[email protected]> wrote: >> I was under the impression that taking the address was more than a single >> load instruction and would emit a placeholder invalid value: which would >> make that technically unsafe in a threaded context. >> >> Sent from my iPhone >> >>> On Oct 12, 2016, at 8:18 AM, Daniel Dunbar via swift-users >>> <[email protected]> wrote: >>> >>> I suspect one of the actual compiler people might tell me I shouldn't trust >>> this, but in practice it works: >>> -- >>> import Darwin.C >>> >>> public class AtomicInt32 { >>> public fileprivate (set) var value : Int32 = 0 >>> >>> /// Create a new atomic integer with the specified initial value. >>> public init(_ value: Int32 = 0) { >>> self.value = value >>> } >>> >>> /// Add one to the value. >>> public func increment () { >>> OSAtomicIncrement32(&value) >>> } >>> } >>> >>> public func +=(int: AtomicInt32, value: Int32) { >>> OSAtomicAdd32(value, &int.value) >>> } >>> -- >>> >>> Would also love to know if compiler guarantees I *can* trust this. >>> >>> Note that this has to be a class for this to be in any way safe, which >>> means it is also rather inefficient if the use case was having a lot of >>> them. >>> >>> - Daniel >>> >>>> On Oct 12, 2016, at 12:47 AM, Gerriet M. Denkmann via swift-users >>>> <[email protected]> wrote: >>>> >>>> >>>> How to translate this to Swift: >>>> >>>> __block atomic_uint_fast64_t counter = ATOMIC_VAR_INIT(0); >>>> dispatch_apply( nbrInterations, queue, ^void(size_t idx) >>>> { >>>> uint64_t tCount = 0; >>>> ... do some counting ... >>>> atomic_fetch_add_explicit( &counter, tCount, memory_order_relaxed ); >>>> } >>>> ) >>>> >>>> Currently I am using: >>>> >>>> var counter: UInt64 = 0 >>>> let dsema = DispatchSemaphore(value: 1) >>>> DispatchQueue.concurrentPerform( iterations: nbrInterations ) >>>> { ( idx: size_t) -> Void in >>>> >>>> var tCount: UInt64 = 0 >>>> ... do some counting ... >>>> _ = dsema.wait(timeout: .distantFuture) >>>> counter += tCount; >>>> dsema.signal() >>>> } >>>> >>>> Is there a better way? >>>> >>>> Gerriet. >>>> >>>> _______________________________________________ >>>> swift-users mailing list >>>> [email protected] >>>> https://lists.swift.org/mailman/listinfo/swift-users >>> >>> _______________________________________________ >>> swift-users mailing list >>> [email protected] >>> https://lists.swift.org/mailman/listinfo/swift-users >> _______________________________________________ >> swift-users mailing list >> [email protected] >> https://lists.swift.org/mailman/listinfo/swift-users
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