为什么在使用 ContinueWith 执行任务时 Windows 表单 UI 被阻塞？

Question

我花了几天时间在 Google 中搜索并试图理解为什么在我的情况下 Windows 表单 UI 被阻止 在 Tasks 中执行 ping。我看到了很多类似的案例，但其中 none 解释了我的具体案例。

问题描述：

我有一个异步发送 ping 的应用程序。每个 ping 都在任务内部发送。我使用 .ContinueWith 接收 ping 的结果并将其打印到文本框而不阻塞 UI 线程。 如果我启动所有 ping 一次就可以正常工作。 如果我添加一个 while {run} 循环使它们永远运行我的 UI 变得无响应并被阻止， none 的结果打印到文本框。

有问题的代码：

Action action2 = () => {
        for (int i = 0; i < ipquantity; i++)
        {
            int temp1 = i;
            string ip = listView1.Items[temp1].SubItems[1].Text;

            if (finished[temp1] == true) // Variable helps to check if ping reply was received and printed
                continutask[temp1] = Task<string>.Run(() => PingStart(ip, temp1)).ContinueWith(antecedent => PrintResult(antecedent.Result, temp1));
        }
};

while (run)
{
    action2();
    Thread.Sleep(1000);
}

问题：

为什么 UI 被 while 循环阻塞，为什么没有它就不会被阻塞？
我如何修改我的代码以仍然能够在不阻塞 UI 的情况下使用 Tasks 进行 ping？
有没有更好的方法可以同时向多个 IP 地址发起无限 ping？

完整代码：

private async void buttonStart_Click(object sender, EventArgs e)
{
    run = true;

    int count = listView1.Items.Count;
    task = new Task<string>[count];
    result1 = new string[count];
    finished = new bool[count];
    continutask = new Task[count];
    for (int i = 0; i < count; i++)
    {
        finished[i] = true;
    }

        Action action2 = () =>
    {
        for (int i = 0; i < count; i++)
        {
            int temp1 = i;
            string ip = listView1.Items[temp1].SubItems[1].Text;


            if (finished[temp1] == true)
                continutask[temp1] = Task<string>.Run(() => PingStart(ip, temp1)).ContinueWith(antecedent => PrintResult(antecedent.Result, temp1));

        }
    };
    while (run)
    {
        action2();
        //await Task.Delay;
        //Thread.Sleep(1000);
    }
}

public void PrintResult(string message, int seqnum)
{
    Action action = () =>
    {
        textBox1.AppendText(message);
        textBox1.AppendText(Environment.NewLine);
        textBox1.AppendText("");
        textBox1.AppendText(Environment.NewLine);
    };
    if (InvokeRequired)
        Invoke(action);
    else
        action();
    finished[seqnum] = true;
}

public string PingStart(string ip, int seqnum)
{
    finished[seqnum] = false;

    Ping isPing = new Ping();
    PingReply reply;
    const int timeout = 2000;
    const string data = "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa";
    var buffer = Encoding.ASCII.GetBytes(data);
    PingOptions options = new PingOptions();
    // Use the default Ttl value which is 128,
    options.DontFragment = false;

    reply = isPing.Send(ip, timeout, buffer, options);
    string rtt = (reply.RoundtripTime.ToString());

    string success = "N/A";

    if (reply.Status == IPStatus.Success)
    {
        success = $"{ip}" + " Success!" + $" rtt: [{rtt}]" + $"Thread: {Thread.CurrentThread.GetHashCode()} Is pool thread: {Thread.CurrentThread.IsThreadPoolThread}";
    }
    else if (reply.Status != IPStatus.Success)
    {
        success = $"{ip}" + $" Not Successful! Status: {reply.Status}" + $"Thread: {Thread.CurrentThread.GetHashCode()} Is pool thread: {Thread.CurrentThread.IsThreadPoolThread}";
    }

    return success;
}

Answer 1

Thread.Sleep(n) 阻塞当前线程 n 毫秒。如果我正确理解代码，它会执行 action2 然后暂停 calling 线程一秒钟。如果该线程是主 (UI) 线程，您的 UI 将被阻塞。

也许将 while 循环移动到另一个线程可以解决问题。

Answer 2

由于您已经创建（并保存）了任务，最简单的解决方法是在 while 循环的每次迭代中等待它们：

while (run)
{
    action2();

    foreach (Task t in continutask)
        await t;
}

这样，当所有 ping 完成（成功与否）后，您将立即重新开始整个过程。

还有一件事：您可以将 textBox1.ScrollToEnd(); 添加到 PrintResult

由于还有很大的改进空间，下面是一个重写和简化的例子。我删除了许多未使用的变量（例如 seqnum）并使 PingStart 方法完全异步。我还将您的 ListBox 替换为 TextBox 以便于测试，因此您可能希望在代码中还原它。

这仍然不是所有可能实现中最干净（主要是因为全局run）但它应该向您展示如何做事"more async" :)

private async void buttonStart_Click(object sender, EventArgs e)
{
    // If the ping loops are already running, don't start them again
    if (run)
        return;

    run = true;

    // Get all IPs (in my case from a TextBox instead of a ListBox
    string[] ips = txtIPs.Text.Split(new[] {"\r\n"}, StringSplitOptions.RemoveEmptyEntries);

    // Create an array to store all Tasks
    Task[] pingTasks = new Task[ips.Length];

    // Loop through all IPs
    for(int i = 0; i < ips.Length; i++)
    {
        string ip = ips[i];

        // Launch and store a task for each IP
        pingTasks[i] = Task.Run(async () =>
            {
                // while run is true, ping over and over again
                while (run)
                {
                    // Ping IP and wait for result (instead of storing it an a global array)
                    var result = await PingStart(ip);

                    // Print the result (here I removed seqnum)
                    PrintResult(result.Item2);

                    // This line is optional. 
                    // If you want to blast pings without delay, 
                    // you can remove it
                    await Task.Delay(1000);
                }
            }
        );
    }

    // Wait for all loops to end after setting run = false.
    // You could add a mechanism to call isPing.SendAsyncCancel() instead of waiting after setting run = false
    foreach (Task pingTask in pingTasks)
        await pingTask;
}

// (very) simplified explanation of changes:
// async = this method is async (and therefore awaitable)
// Task<> = This async method returns a result of type ...
// Tuple<bool, string> = A generic combination of a bool and a string
// (-)int seqnum = wasn't used so I removed it
private async Task<Tuple<bool, string>> PingStart(string ip)
{
    Ping isPing = new Ping();
    const int timeout = 2000;
    const string data = "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa";
    var buffer = Encoding.ASCII.GetBytes(data);
    PingOptions options = new PingOptions {DontFragment = false};

    // await SendPingAsync = Ping and wait without blocking
    PingReply reply = await isPing.SendPingAsync(ip, timeout, buffer, options);
    string rtt = reply.RoundtripTime.ToString();

    bool success = reply.Status == IPStatus.Success;
    string text;

    if (success)
    {
        text = $"{ip}" + " Success!" + $" rtt: [{rtt}]" + $"Thread: {Thread.CurrentThread.GetHashCode()} Is pool thread: {Thread.CurrentThread.IsThreadPoolThread}";
    }
    else
    {
        text = $"{ip}" + $" Not Successful! Status: {reply.Status}" + $"Thread: {Thread.CurrentThread.GetHashCode()} Is pool thread: {Thread.CurrentThread.IsThreadPoolThread}";
    }

    // return if the ping was successful and the status message
    return new Tuple<bool, string>(success, text);
}

这样，您将为每个 IP 建立一个循环，该循环将彼此独立地继续，直到 run 设置为 false。

为什么在使用 ContinueWith 执行任务时 Windows 表单 UI 被阻塞？

Why is the Windows Forms UI blocked when executing Task with ContinueWith?

c#

winforms

task-parallel-library

blocked

continuewith

问题描述：

问题：

完整代码：