.NET Core 3.1 HttpClient 间歇性抛出异常：SocketException: I/O 操作已被中止，因为线程退出或

Question

我偶尔会遇到以下异常：

IOException：无法从传输连接中读取数据： 由于线程退出或 申请要求..

SocketException: I/O 操作已被中止，因为 线程退出或应用程序请求。

系统正在查询外部资源，有时会发生异常，但似乎没有任何异常。我试图为HttpClient 设置更长的超时时间，但没有帮助。在异常发生之前，它可能是 5000-50000 次搜索，但我仍然想减轻它。如果我在出现异常后直接重试相同的搜索，它会起作用，因此即使我无法访问该应用程序日志，接收方似乎也没有问题。在.NET Core 3.1 上运行。

MyService.cs

public class MyService
{

    private readonly HttpClient _httpClient;

    public MyService(HttpClient client)
    {
        client.BaseAddress = new Uri("https://example.com/");
        client.Timeout = TimeSpan.FromMinutes(5);
        _httpClient = client;
    }
    
    private async Task<List<string>> GetValuesFromSearch(string search)
    {
        //Exception is thrown here
        var response = await _httpClient.GetAsync("search/" + search);

        using var responseStream = await response.Content.ReadAsStreamAsync();
        
        response.EnsureSuccessStatusCode();

        var searchResultList = await JsonSerializer.DeserializeAsync
            <List<string>>(responseStream);

        return searchResultList;
    }
}

这样称呼：

var myService = new MyService(new HttpClient());

foreach (var search in listToIterate)
{
    //Can be called up to 200 000 times
    var result = await myService.GetValuesFromSearch(search);
}

Answer 1

问题可能是由socket exhaustion 引起的。这是 HttpClient 的一个已知问题，解决方案是使用 HttpClientFactory。我没有对此进行测试，但这里是您的 MyService 类的快速重写：

public class MyService
{
    private readonly IHttpClientFactory _httpClientFactory;

    public MyService(IHttpClientFactory httpClientFactory)
    {
        _httpClientFactory = httpClientFactory ??
            throw new ArgumentNullException(nameof(httpClientFactory));
    }

    private async Task<List<string>> GetValuesFromSearch(string search)
    {
        var _httpClient = _httpClientFactory.CreateClient("MyClient");

        _httpClient.BaseAddress = new Uri("https://example.com/");
        _httpClient.Timeout = TimeSpan.FromMinutes(5);

        // You could also set the above in Startup.cs or wherever you add your services:
        //services.AddHttpClient("MyClient", c => {
        //    c.BaseAddress = new Uri("https://example.com/");
        //    c.Timeout = TimeSpan.FromMinutes(5);
        //});

        //Exception is thrown here
        var response = await _httpClient.GetAsync("search/" + search);

        using var responseStream = await response.Content.ReadAsStreamAsync();

        response.EnsureSuccessStatusCode();

        var searchResultList = await JsonSerializer.DeserializeAsync
            <List<string>>(responseStream);

        return searchResultList;
    }
}

Answer 2

如果您的请求未能返回 HttpResponseMessage，HttpClient 将把它作为 TaskCancelledException 类型的内部异常堆栈跟踪抛出。要确认，请尝试使用 Polly 添加 TimeoutAsync 策略；异常应更改为 TimeOutRejectedException。

在类似的用例中，我发现的最佳解决方案是：

• 使用 HttpClientFactory，使用客户端时使用 skip the using statement。
• use Polly to build in some additional resiliency。
• 将 HttpClient 代码包装在 try/catch 块中，这样您的进程就不会在没有 HttpResponseMessage 可使用的情况下崩溃（这是实际的“修复”，另外两个部分是为了防止异常经常投掷）：

private async Task<List<string>> GetValuesFromSearch(string search)
    {
        try
            {
                //Exception is thrown here
                var response = await _httpClient.GetAsync("search/" + search);

                var responseStream = await response.Content.ReadAsStreamAsync();

                response.EnsureSuccessStatusCode();

                var searchResultList = await JsonSerializer.DeserializeAsync
                    <List<string>>(responseStream);

                return searchResultList;
            }
        catch (Exception ex)
            {
                // Log the exception. 
                // Do what you want, or return null and handle a dropped request in your calling method.
            }
    }