class ThreadSafeDictionary<K: Hashable, T> {
    private var dictionary: [K: T] = [:]
    private let queue = DispatchQueue(label: "threadSafeDictionaryQueue", attributes: .concurrent)

    subscript(key: K) -> T? {
        get {
            return queue.sync { dictionary[key] }
        }
        set {
            queue.async(flags: .barrier) { self.dictionary[key] = newValue }
        }
    }
}