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
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