ASP.net HttpRequest 上的静态 HttpClient 线程安全

Question

我们正在为 HttpClient 创建一个包装器。因为我们将遵循 https://github.com/mspnp/performance-optimization 中的性能优化指南。我们想避免 anti-pattern - 该文档中提到的不正确的实例化。我将此指南推荐给了我的团队以使用静态 HttpClient。我得到的反馈是 thread-safety。每个请求都有一个 header 包含用户声明。由于我有一个静态的 HttpClient，它会是 thread-safe 吗？如果我们有多个请求同时命中代码（例如 GET），设置 header 是否会成为竞争条件？我们有如下实现。

public class HttpClientHelper{
private static readonly HttpClient _HttpClient;
static HttpClientHelper() {
        HttpClient = new HttpClient();
        HttpClient.Timeout = TimeSpan.FromMinutes(SOME_CONFIG_VALUE);
}

public async Task<HttpResponseMessage> CallHttpClientPostAsync(string requestUri, HttpContent requestBody)
{
    AddHttpRequestHeader(httpClient);
    var response = await httpClient.PostAsync(requestUri, requestBody); //Potential thread synchronization issue???
    return response;
}

public HttpResponseMessage CallHttpClientGet(string requestUri)
{
    AddHttpRequestHeader(httpClient);
    var response = httpClient.GetAsync(requestUri).Result; //Potential thread synchronization issue???
    return response;
}

private void AddHttpRequestHeader(HttpClient client)
{
    string HeaderName = "CorrelationId";
    client.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue(Properties.Settings.Default.HttpClientAuthHeaderScheme, GetTokenFromClaims()); //Race condition???
    if (client.DefaultRequestHeaders.Contains(HeaderName))
        client.DefaultRequestHeaders.Remove(HeaderName);
    client.DefaultRequestHeaders.Add(HeaderName, Trace.CorrelationManager.ActivityId.ToString());
}

}

Answer 1

您的团队是正确的，这远非线程安全。考虑这种情况：

线程 A 将 CorrelationId header 设置为 "foo"。
线程 B 将 CorrelationId header 设置为 "bar"。
线程A发送请求，其中包含线程B的CorrelationId。

更好的方法是让您的 CallXXX 方法创建新的 HttpRequestMessage objects, and set the header on those, and use HttpClient.SendAsync 来进行调用。

另请记住，re-using HttpClient 实例仅在您对同一主机进行多次调用时才有用。

ASP.net HttpRequest 上的静态 HttpClient 线程安全

Static HttpClient thread safe on ASP.net HttpRequest

asp.net

thread-safety

httprequest

static-libraries

dotnet-httpclient