protocol AppModelRequest {
    func execute(model: SpecificAppModel)
}

protocol AppModel: AnyObject {
    func perform(_ request: AppModelRequest)
}

class SpecificAppModel: AppModel {
    private let queue = DispatchQueue(label: "AppModelQueue")
    public func perform(_ request: AppModelRequest) {
        queue.async {
            request.execute(model: self)
        }
    }
}