DispatchGroup无法与URLSession.shared.dataTask一起使用

Question

我正在尝试通过URLSession.shared单例实现许多并发api调用。我想要的是它们是同时进行的，所以当我收到所有响应时，然后执行完成处理程序（我以这个示例为例：https://medium.com/@oleary.audio/simultaneous-asynchronous-calls-in-swift-9c1f5fd3ea32）：

init(completion: (()->Void)? = nil) throws {
    self.myToken = myToken

    let group = DispatchGroup()

    group.enter()
    print("Downloading User")

    self.downloadUser(completion: { userObject in
        self.userObject = userObject
        group.leave()
    })

    group.enter()
    print("Downloading Tickets")

    self.downloadTickets(completion: { ticketsObject in
        if let ticketsObject   = ticketsObject {
            self.ticketsObject = ticketsObject
        }
        group.leave()
    })

    group.wait()

    completion?()
}

然后实现api调用的函数如下：

private func downloadUser( completion: @escaping ((myUsuario)->Void )) {
    let url = URL(string: "\(Globals.laravelAPI)me")
    var request = URLRequest(url: url!)
    let task = URLSession.shared.dataTask(with: request) {
        (data:Data?, response:URLResponse?, error:Error?) in

        if let error = error {
            ...
        }
        guard let httpResponse = response as? HTTPURLResponse,(200...299).contains(httpResponse.statusCode) else { ... }
        if let data = data {
            do {
                let user = try JSONDecoder().decode(myUsuario.self, from: data)
                completion(user)
            } catch {
                print("USER PARSING ERROR: \(error)")
                fatalError()
            }
        }
    }
    task.resume()
}

当我运行该程序时，它会进行调用，但从未得到响应，因此group.wait()从未执行。