GCDLock.swift

import Foundation

final class GCDLock<Value> {
    var value: Value
    let queue = DispatchQueue(label: "")
    init(value: Value) {
        self.value = value
    }

    func read() -> Value {
        var value: Value?
        queue.sync {
            value = self.value
        }
        return value!
    }

    func write(_ newValue: Value) {
        queue.async {
            self.value = newValue
        }
    }
}

// Example use case
final class Example {
    private var counterLock: GCDLock<Int> = GCDLock(value: 0)
    var counter: Int {
        get { return counterLock.read() }
        set { counterLock.write(newValue) }
    }
}