GCD barrier in iOS

gcd_barrier.swift

  class MutiReadSingleWriteObject<T> {
        
        let queue = DispatchQueue(label: "com.readwrite.concurrency", attributes: .concurrent)
        var _object:T?
        
        var object: T? {
            @available(*, unavailable)
            get {
                fatalError("You cannot read from this object.")
            }
            
            set {
                queue.async(flags: .barrier) {
                    self._object = newValue
                }
            }
        }
        
        func getObject(_ closure: @escaping (T?) -> Void) {
            queue.async {
                closure(self._object)
            }
        }
    }
    
    func testMutiReadSingleWriteObject() {
        let store = MutiReadSingleWriteObject<Int>()
        let queue = DispatchQueue(label: "com.come.concurrency", attributes: .concurrent)
        
        for i in 0...100 {
            queue.async {
                store.getObject { obj in
                    print("\(i) -- \(String(describing: obj))")
                }
            }
        }
        print("pre --- ")
        store.object = 1
        print("after ---")
        store.getObject { obj in
            print("finish result -- \(String(describing: obj))")
        }
        
    }