线程池友好的睡眠方法？

Question

我想在 ASP.net 应用程序中插入一个睡眠（又名节流、延迟、缓缓、停留）（想象一下类似失败的登录尝试升级延迟）。

protected void Page_Load(object sender, EventArgs e)
{
    Int32 sleepyTime = GetSleepyTime(Request);

    if (sleepyTime > 0)
        System.Threading.Thread.Sleep(sleepyTime);


    //...Continue normal processing
}

我希望所有剩余的处理继续正常进行；我只是想让用户代理受苦。

问题是 ASP.net 使用线程池来处理请求。如果我要 Sleep 5、10、30 秒，我就会吃掉宝贵的有限资源。

我想它应该是这样的：

protected void Page_Load(object sender, EventArgs e)
{
    Int32 sleepyTime = GetSleepyTime(Request);

    if (sleepyTime > 0)
       ABetterKindOfSleep(sleepyTime);

    //...Continue normal processing
}

private void ABetterKindOfSleep(int milliseconds)
{
   await SleepAsync(milliseconds);
}

private async void SleepAsync(int milliseconds)
{
   System.Threading.Thread.Sleep(milliseconds);
}

但从未编写过任何 async/await 代码，也不了解 async 和 await 去向、原因或原因背后的逻辑，即使它可以用于运行异步代码：不知道能不能用来[=44=]异步代码

红利阅读

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Asynchronous Thread.Sleep()

Answer 1

async 等价于 Thread.Sleep 是 await Task.Delay:

if (sleepyTime > 0)
  await Task.Delay(sleepyTime);

请注意，这必须在 async 方法的上下文中使用，并且在可以使用 async 的地方存在限制（特别是在 WebForms 上）。有关详细信息，请参阅我的 article on async ASP.NET and the official tutorial on async WebForms.

Answer 2

很简单。

首先你创建一个 IHttpModule class:

class TarpitHttpModule : IHttpModule
{
}

然后通过在 web.config:

中注册让 IIS 知道这个模块

<configuration>
   <system.webServer>
      <modules runAllManagedModulesForAllRequests="true">
         <add name="Tarpit" type="TarpitHttpModule"/>

如果你是卡西尼，加到：

<configuration>
   <system.web>
      <httpModules>
         <add name="Tarpit" type="TarpitHttpModule"/>

只要有 http 请求进来，IIS 就会调用您的 .Init 方法。这是您将使用以下方式注册异步事件处理程序的地方：

Application.AddOnBeginRequestAsync: Adds the specified BeginRequest event to the collection of asynchronous BeginRequest 当前请求的事件处理程序。

代码：

public void Init(HttpApplication application)
{
    //This is the synchronous event handler; which we don't want
    //application.BeginRequest += new EventHandler(this.Application_BeginRequest);

    //EventHandlerTaskAsyncHelper requires .NET 4.5
    //https://brockallen.com/2013/07/27/implementing-async-http-modules-in-asp-net-using-tpls-task-api/ 
    //  Archive: http://archive.is/Cdvle
    //
    //Normally you'd have to write a pair of methods:
    //    application.AddOnBeginRequestAsync(OnBegin, OnEnd);
    //
    //and then we'd have to write an OnBegin which returns IAsyncResult, and then OnEnd which takes the IAsyncResult.
    //The modern way is to use Tasks, and use the IAsyncResult that a Task **is**.
    //Fortunately the .NET team wrote a handy class that wraps up the boilerplate catching faults, etc,
    //and created the EventHandlerTaskAsyncHelper class

    var beginTaskHelper = new EventHandlerTaskAsyncHelper(BeginRequestAsync);
    application.AddOnBeginRequestAsync(beginTaskHelper.BeginEventHandler, beginTaskHelper.EndEventHandler);
}

所以现在我们必须提供 BeginRequestAsync 异步处理程序：

async Task BeginRequestAsync(object sender, EventArgs e)
{
    var application = (HttpApplication)sender;
    var context = application.Context;

    // In reality i would use the context.Request to come up with a unique key 
    // for this user agent e.g. 
    String key = SHA256(UserHostAddress+UserAgent+AcceptTypes+UserLanguages).ToBase64();
    // And use that as a cache key store information about this user agent
    Object tarpitInfo = context.Cache.Get(agentIdentity);
    if (ti == null)
        return;

    // But in this SO demo, i'm just going to unconditionally sleep
    Boolean waitPerformed = await PerformDelay(context, tarpitInfo);
    if (waitPerformed)
    {
        context.Response.StatusCode = 429;
        context.Response.StatusDescription = "Too Many Requests";
        context.Response.End();
        return;
    }
}

然后是睡觉的工作：

async Task<Boolean> PerformDelay(HttpContext context, TarInfo ti)
{
    int delayMs = 3000;
    Task delay = Task.Delay(delayMs);
    await delay;
    return true;
}

Answer 3

我还想阻止机器人流量攻击登录端点，我担心如果我只是等待，我会达到最大并发请求或运行内存不足。我还没有找到使用 Windows 和 Asp.Net.

执行此操作的低开销方法

我喜欢它 done here 的方式，它改变了 TCP/IP 堆栈的行为以缩小 window 大小而不是 ACK 后续数据包，这使得远程以指数方式返回关闭，只发送少量数据。

我可能会在前面添加一些 Linux 虚拟机运行ning HAProxy 以利用其 DDOS capabilities

线程池友好的睡眠方法？

Thread-pool friendly approach to Sleep?

.net

asp.net

iis

httpmodule

红利阅读