Swift异步请求循环复制

Question

我正在创建一个Xcode命令行实用程序应用程序，该应用程序应从JSON文件读取URL，并检查每个URL以查看其是否返回200 HTTP代码。到目前为止，我已经知道了：

  Services.shared.readJsonFile { file in

        if file == nil {
            print("File does not exist!")
            print(FileManager.default.currentDirectoryPath)
            exit(EXIT_SUCCESS)
        }

        let dispatchGroup = DispatchGroup()

            for servers in (file?.monitors)! {

                dispatchGroup.enter()

                let urlString = servers.url

                print("1")

                Services.shared.checkConnection(url: urlString, id: servers.component_id) { conresult in

                     print("2")

                    if conresult == .down {

                        print("\(urlString) is DOWN!")


                    } else {

                        print("\(urlString) is UP!")


                    }

                    dispatchGroup.leave()

                }

            }

            dispatchGroup.notify(queue: .main) {

                exit(EXIT_SUCCESS)
            }

    }

    dispatchMain()

它应该遍历每个URL并打印该URL是向上还是向下，但是输出如下：

1
1
2
https://esg3g2sdg32.com is DOWN!
2
https://esg3g2sdg32.com is DOWN!
logout

最终会打印1次，然后再打印2次，而不是一次打印1次和2次。

更新： 添加了信号灯：

Services.shared.readJsonFile { file in

    print(FileManager.default.currentDirectoryPath)

    if file == nil {
        print("File does not exist!")
        //print(FileManager.default.currentDirectoryPath)
        exit(EXIT_SUCCESS)
    }

    let semaphore = DispatchSemaphore(value: 1)
    let dispatchQueue = DispatchQueue(label: "taskQueue")
    let dispatchGroup = DispatchGroup()


        for servers in (file?.monitors)! {

        dispatchQueue.async {

            dispatchGroup.enter()
            semaphore.wait()

            let urlString = servers.url

            print("1")

            Services.shared.checkConnection(url: urlString, id: servers.component_id) { conresult in

                print("2")

                if conresult == .down {

                    print("\(urlString) is DOWN!")


                } else {

                    print("\(urlString) is UP!")

                }

                dispatchGroup.leave()
                semaphore.signal()
            }

        }
    }

        dispatchGroup.notify(queue: .main) {

            //exit(EXIT_SUCCESS)
        }

}

dispatchMain()

现在输出如下：

1
2
https://google.com is UP!
1
2
https://esg3g2sdg32.com is DOWN!
2
https://esg3g2sdg32.com is DOWN!
Illegal instruction: 4
logout

首先打印1,2个URL，然后再打印1,2个和第二个URL，然后又只打印2个和第二个URL。