Synchronize Properties in Swift 3 using GCD

Question

I watched this years WWDC GCD talk lately and I think there is a code snippet something is wrong with. It is about making a property thread-safe using D

Answer 1

I'd like just to show another approach that makes you able to read concurrently, but block everything while writing by using a dispatch barrier.

class MyObject {
private var internalState: Int
private let internalQueue = DispatchQueue(label: "reader-writer", attributes: .concurrent)

var state: Int {
    get {
        return internalQueue.sync { internalState }
    }

    set (newState) {
        internalQueue.async(flags: .barrier) { internalState = newState }
    }
  }
}

With that approach, reads can occur concurrently on the queue, but writes are executed exclusively, due to the barrier.

This is just a Swift 3 conversion of an approach explained in the book Effective Objective C 2.0, written by Matt Galloway.