Using queues.swift

let queue = dispatch_queue_create("QUEUE", DISPATCH_QUEUE_CONCURRENT)

var holder: Int = 10

func readSafe() -> Int {
    var read: Int!
    dispatch_sync(queue) {
        read = holder
    }
    return read
}

func writeSafe(value: Int) {
    dispatch_barrier_async(queue) {
        holder = value
    }
}