多个 HTTP 请求触发 HTTP Client 超时 [英] Multiple HTTP requests trigger HTTP Client timeout

问题描述

我有一个应用异步发送 500 个 HTTP 请求.由于 HTTP 客户端超时， 15 秒后处理的所有请求都会失败，即使请求的端点已经返回 200 OK.

I have an app that's sending 500 HTTP requests asynchronously. All requests processed after 15 seconds fail because of the timeout on the HTTP Client, even when the requested endpoint already returned a 200 OK.

代码非常简单.这里我们获取一大块请求 (500)，并异步执行它们.需要注意的是，下面的函数是运行在基于消费的计划上的Azure函数.

The code is very straight-forward. Here we take a chunk of requests (500), and execute them asynchronously. It should be noted that the function below is an Azure function running on the consumption-based plan.

    public async Task RunBatch(List<Request> requests)
    {
        if (requests != null && requests .Count > 0)
        {
            var tasks = new Task[requests.Count];
            var i = 0;
            foreach (var request in requests)
            {
                var request = new HttpRequestMessage(HttpMethod.Post, new Uri(request.Url));
                request.Content = new StringContent(request.BodyString, Encoding.UTF8, "application/json");
                tasks[i] = _httpClient.SendAsync(request);
                i++;
            }

            await Task.WhenAll(tasks);
        }
    }

以下代码存在于我的构造函数中

The following code exists in my constructor

_httpClient = new HttpClient();
_httpClient.Timeout = new TimeSpan(0, 0, 15); // 15 seconds

这是来自 Azure 的日志.

Here are logs from Azure.

我希望每个请求的超时时间为 15 秒.但是，每当我的服务器开始处理等待的请求时，我都需要它给我一个准确的响应代码.这可能吗?

I'd like each request to have a timeout of 15 seconds. However, I need it to give me an accurate response code whenever my server gets around to processing the awaited request. Is this possible?

我应该注意:使用更高的 Http 超时(1 分钟)，所有请求都会成功.

I should note: with a higher Http timeout (1 min), all requests succeed.

推荐答案

就我个人而言，我认为尝试发出 500 个并发请求总是容易出错.您提到您是异步执行的，但实际上，当您启动 500 个热"程序时，您的代码中并没有很多异步.任务然后等待它们全部完成.

Personally, I think attempting to issue 500 concurrent requests is always going to be error prone. You mention that you're doing it asynchronously, but in reality there's not a whole lot of asynchrony in your code as you fire-up 500 "hot" tasks then wait for them all to finish.

我会使用信号量来控制一次可以发出多少请求.您可能需要玩弄数字才能找到最佳位置.

I would use a semaphore to control how many requests can be made at once. You may have to play with the numbers to find the sweet spot.

以下代码在 LINQPad 中运行良好(尽管 bing 很快注意到奇数个请求并开始向页面添加验证码):

The following code works well in LINQPad (although bing quickly notices the odd number of requests and starts adding a CAPTCHA to the page):

// using System.Threading;
async Task Main()
{
    var httpClient = new HttpClient();
    var urls = Enumerable.Range(1, 500).Select(e => "https://www.bing.com/").ToList();
    
    // 10 concurrent requests - tweak this number
    var semaphore = new SemaphoreSlim(10, 10);
    
    var tasks = urls.Select(u => MakeRequest(u, semaphore, httpClient));
        
    var allResponses = await Task.WhenAll(tasks);
    
    // Do something with allResponses
}

private async Task<string> MakeRequest(string url, SemaphoreSlim semaphore, HttpClient httpClient)
{
    try
    {
        await semaphore.WaitAsync();
        var request = new HttpRequestMessage(HttpMethod.Get, new Uri(url));
        var response = await httpClient.SendAsync(request);
        
        // Add an optional delay for further throttling:
        //await Task.Delay(TimeSpan.FromMilliseconds(100));
        
        return await response.Content.ReadAsStringAsync();
    }
    finally
    {
        semaphore.Release();
    }
}

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