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.我们将遵循https://github.com/mspnp/performance-optimization的性能优化指南.我们希望避免反模式 - 该文档中提到的不正确的实例化.我将此指南提交给我的团队使用静态HttpClient.我得到的反馈是线程安全性.每个请求都有一个包含用户声明的标头.由于我有一个静态的HttpClient,它是否是线程安全的？如果我们同时有多个请求命中代码(例如GET),那么设置标题是否会出现竞争条件？我们的实施如下.

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

你的团队是正确的,这远非线程安全.考虑这种情况:

• 线程A将CorrelationId标头设置为"foo".
• 线程B将CorrelationId标头设置为"bar".
• 线程A发送请求,其中包含线程B的CorrelationId.

一种更好的方法是让您的CallXXX方法创建新的HttpRequestMessage对象,并在这些对象上设置标头,并使用HttpClient.SendAsync进行调用.

请记住,重复使用HttpClient实例仅在您对同一主机进行多次调用时才有用.