为什么在使用 ContinueWith 执行任务时 Windows 窗体 UI 被阻止? [英] Why is the Windows Forms UI blocked when executing Task with ContinueWith?
问题描述
我花了几天时间在 Google 中搜索并试图了解为什么在我的情况下，在 任务 中执行 ping 时，Windows 窗体 UI 被阻止.我看到了很多类似的案例，但没有一个能解释我的具体案例.
I spent a couple of days searching in Google and trying to understand why in my case Windows Forms UI is blocked when executing pings in Tasks. I saw a lot of similar cases, but none of them explains my specific case.
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.如果我一次启动所有 ping 就可以正常工作.如果我添加一个 while {run} 循环让它们永远运行，我的 UI 变得无响应并被阻止，并且没有任何结果打印到文本框.
I have an application which sends pings asynchronously. Each ping is send inside of a Task. I use .ContinueWith to receive result of a ping and print it to textbox without blocking UI thread. It works OK if I launch all pings once. If I add a while {run} loop to make them run forever my UI becomes unresponsive and blocked, and none of the results are printed to the textbox.
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 会被
while循环阻塞，为什么没有它就不会被阻塞? - 如何修改我的代码，以便在不阻塞 UI 的情况下仍然能够使用 Tasks 进行 ping 操作?
- 有没有更好的方法可以同时向多个 IP 地址发起无休止的 ping 操作?
- Why is the UI blocked with a
whileloop and why is it not blocked without it? - How can I modify my code to be still able to use Tasks for pings without blocking the UI?
- Is there a better way to launch endless pings to several IP addresses simultaneously?
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;
}
推荐答案
由于您已经创建(并保存)了您的任务，最简单的解决方法是在 while 循环的每次迭代中等待它们:
Since you already create (and save) your tasks, the easiest fix would be to await them for each iteration of your while loop:
while (run)
{
action2();
foreach (Task t in continutask)
await t;
}
这样，当所有 ping 完成(成功与否)后，您将再次开始整个过程 - 毫不拖延.
That way, when all pings completed (successful or not) you start the entire process again - without delay.
还有一件事:你可以添加一个 textBox1.ScrollToEnd(); 到 PrintResult
One more thing: You could add a textBox1.ScrollToEnd(); to 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恢复它.
Since there is a lot of room for improvement, below is a rewritten and simplified example. I've removed a lot of unused variables (e.g. seqnum) and made the PingStart method completely asynchronous. I also replaced your ListBox with a TextBox for easier testing, so you might want to revert that in your code.
这仍然不是所有可能实现中最干净的(主要是因为全局run)，但它应该向您展示如何做more异步" :)
This still isn't the cleanest of all possible implementations (mainly because of the global run) but it should show you how to do things "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，每个 IP 都会有一个循环，该循环将彼此独立地继续，直到 run 设置为 false.
This way you will have a loop for each IP that will continue independently of each other until run is set to false.
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