c# - 如何限制与 Async HttpClient C# 的连接

Question

我正在尝试限制与端点之间的最大连接数，我通过设置 ServicePointManager.DefaultConnectionLimit 来执行此操作，但它不起作用。为了对此进行测试，我设置了一个休眠 5 秒然后返回的端点。

这是我的代码:

class Program
{
    private static Uri uri = new Uri("http://myservice.com?sleepForMillisecond=5000"));

    static void Main(string[] args)
    {
        ServicePointManager.DefaultConnectionLimit = 1;
        MainAsync().Wait();
    }

    static async Task MainAsync()
    {
        var watch = Stopwatch.StartNew();
        var tasks = new List<Task>()
            {
                Task.Run(async () => await MakeCallWithHttpClient()),
                Task.Run(async () => await MakeCallWithHttpClient()),
                Task.Run(async () => await MakeCallWithHttpClient())
            };

        await Task.WhenAll(tasks);
        watch.Stop();
        Console.WriteLine("Elapsed Time For HttpClient: " + watch.Elapsed);

        watch.Restart();
        tasks = new List<Task>()
            {
                Task.Run(async () => await MakeCallWithWebClient()),
                Task.Run(async () => await MakeCallWithWebClient()),
                Task.Run(async () => await MakeCallWithWebClient())
            };

        await Task.WhenAll(tasks);
        watch.Stop();
        Console.WriteLine("Elapsed Time For WebClient: " + watch.Elapsed);
        Console.WriteLine("Press Enter To Exit.");
        Console.ReadLine();
    }

    private static async Task MakeCallWithHttpClient()
    {
        var client = new HttpClient();
        await client.GetStringAsync(uri);
        Console.WriteLine("Done");
    }

    private static async Task MakeCallWithWebClient()
    {
        var client = new WebClient();
        await client.DownloadStringTaskAsync(uri);
        Console.WriteLine("Done");
    }
} 

下面是输出:

Done
Done
Done
Elapsed Time For HttpClient: 00:00:05.0953943
Done
Done
Done
Elapsed Time For WebClient: 00:00:15.0450096

如您所见，异步 HttpClient 不受最大连接数 1 的限制，因为并行调用 3 次需要 5 秒，而异步 WebClient 受连接数 1 的限制，因为并行调用 3 次需要 15 秒。

我的问题是...如何使用异步 HttpClient 限制最大连接数？

谢谢。

Answer 1

对所有请求使用相同的 HttpClient 实例，连接限制将按预期工作。