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());
}
}
解决方法
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.
更好的方法是使用CallXXX方法创建新的HttpRequestMessage对象,并在其上设置标题,并使用HttpClient.SendAsync进行调用.
请记住,重新使用HttpClient实例仅在您对同一主机进行多次调用时才有用.
