问题描述
我正在使用.NET Framework 4.6.1。
I am using .NET Framework 4.6.1.
我的web api中有一个控制器，我有静态HttpClient来处理所有的http请求。我在IIS上托管我的应用程序后，大约每月一次，对于我的应用程序的所有传入请求，我收到以下异常：
I have a controller in my web api, where I have static HttpClient to handle all the http requests. After I hosted my app on IIS, approximately once in a month, I get the following exception for all the incoming request to my app:
System.ArgumentNullException: Value cannot be null.
at System.Threading.Monitor.Enter(Object obj)
at System.Net.Http.Headers.HttpHeaders.ParseRawHeaderValues(String name, HeaderStoreItemInfo info, Boolean removeEmptyHeader)
at System.Net.Http.Headers.HttpHeaders.AddHeaders(HttpHeaders sourceHeaders)
at System.Net.Http.Headers.HttpRequestHeaders.AddHeaders(HttpHeaders sourceHeaders)
at System.Net.Http.HttpClient.PrepareRequestMessage(HttpRequestMessage request)
at System.Net.Http.HttpClient.SendAsync(HttpRequestMessage request, HttpCompletionOption completionOption, CancellationToken cancellationToken)
at System.Net.Http.HttpClient.SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
at System.Net.Http.HttpClient.PutAsync(Uri requestUri, HttpContent content, CancellationToken cancellationToken)
at Attributes.Controllers.AttributesBaseController.<UpdateAttributes>d__6.MoveNext() in D:\Git\PortalSystem\Attributes\Controllers\AttributesBaseController.cs:line 42
如果我在IIS上重启应用程序池，一切都开始了工作再好。这是我的代码：
If I restart the app pool on IIS, everything starts to work fine again. Here is the code that I have:
public class AttributesBaseController : ApiController
{
[Inject]
public IPortalsRepository PortalsRepository { get; set; }
private static HttpClient Client = new HttpClient(new HttpClientHandler { Proxy = null, UseProxy = false })
{ Timeout = TimeSpan.FromSeconds(double.Parse(WebConfigurationManager.AppSettings["httpTimeout"])) };
private static readonly Logger logger = LogManager.GetCurrentClassLogger();
protected async Task UpdateAttributes(int clientId, int? updateAttrId = null)
{
try
{
Client.DefaultRequestHeaders.Accept.Clear();
Client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));
#region Update Client Dossier !!! BELOW IS LINE 42 !!!!
using (var response = await Client.PutAsync(new Uri(WebConfigurationManager.AppSettings["dossier"] + "api/dossier?clientId=" + clientId), null))
{
if (!response.IsSuccessStatusCode)
{
logger.Error($"Dossier update failed");
}
}
#endregion
#region Gather Initial Info
var checkSystems = PortalsRepository.GetCheckSystems(clientId);
var currentAttributes = PortalsRepository.GetCurrentAttributes(clientId, checkSystems);
#endregion
List<Task> tasks = new List<Task>();
#region Initialize Tasks
foreach (var cs in checkSystems)
{
if (!string.IsNullOrEmpty(cs.KeyValue))
{
tasks.Add(Task.Run(async () =>
{
var passedAttributes = currentAttributes.Where(ca => ca.SystemId == cs.SystemId && ca.AttributeId == cs.AttributeId &&
(ca.SysClientId == cs.KeyValue || ca.OwnerSysClientId == cs.KeyValue)).ToList();
if (cs.AttributeId == 2 && (updateAttrId == null || updateAttrId == 2))
{
await UpdateOpenWayIndividualCardsInfo(passedAttributes, cs, clientId);
}
else if (cs.AttributeId == 3 && (updateAttrId == null || updateAttrId == 3))
{
await UpdateEquationAccountsInfo(passedAttributes, cs, clientId);
}
else if (cs.AttributeId == 8 && (updateAttrId == null || updateAttrId == 8))
{
await UpdateOpenWayCorporateInfo(passedAttributes, cs, clientId);
}
else if (cs.AttributeId == 9 && (updateAttrId == null || updateAttrId == 9))
{
await UpdateEquationDealsInfo(passedAttributes, cs, clientId);
}
else if (cs.AttributeId == 10 && (updateAttrId == null || updateAttrId == 10))
{
await UpdateOpenWayIndividualCardDepositsInfo(passedAttributes, cs, clientId);
}
else if (cs.AttributeId == 16 && (updateAttrId == null || updateAttrId == 16))
{
await UpdateOpenWayBonusInfo(passedAttributes, cs, clientId);
}
else if (cs.AttributeId == 17 && (/*updateAttrId == null ||*/ updateAttrId == 17))
{
await UpdateExternalCardsInfo(passedAttributes, cs, clientId);
}
if (cs.AttributeId == 18 && (updateAttrId == null || updateAttrId == 18))
{
await UpdateCRSInfo(passedAttributes, cs, clientId);
}
else if (cs.AttributeId == 22 && (updateAttrId == null || updateAttrId == 22))
{
await UpdateCardInsuranceInfo(passedAttributes, cs, clientId);
}
}));
}
}
#endregion
// Run all tasks
await Task.WhenAny(Task.WhenAll(tasks.ToArray()), Task.Delay(TimeSpan.FromSeconds(double.Parse(WebConfigurationManager.AppSettings["taskWaitTime"]))));
}
catch (Exception ex)
{
logger.Error(ex);
}
}
}
任何人都可以给我建议/有助于弄清楚问题？我只是不知道问题是否与我使用HttpClient执行任务或IIS上发生的不良事情有关。
Can anyone give me advice/help to figure out the problem? I just don't know whether the problem is in the way I am using HttpClient with tasks or something bad happens on IIS.
推荐答案
查看 DefaultRequestHeaders 的实现，我们可以看到它使用简单的词典来存储标题：
Looking at the implementation of DefaultRequestHeaders, we can see that it uses a simple Dictionary to store the headers:
private Dictionary<string, HttpHeaders.HeaderStoreItemInfo> headerStore;
DefaultRequestHeaders.Accept.Clear 只是删除了来自字典的密钥，没有任何同步：
DefaultRequestHeaders.Accept.Clear just removes the key from the dictionary, without any kind of synchronization:
public bool Remove(string name)
{
this.CheckHeaderName(name);
if (this.headerStore == null)
return false;
return this.headerStore.Remove(name);
}
Dictionary.Remove 如果您在此操作期间访问字典，则不会发生线程安全，不可预测的行为。
Dictionary.Remove isn't thread-safe, unpredictable behavior can happen if you access the dictionary during this operation.
现在，如果我们查看 ParseRawHeaderValues 方法：
Now if we look at the ParseRawHeaderValues method in your stacktrace:
private bool ParseRawHeaderValues(string name, HttpHeaders.HeaderStoreItemInfo info, bool removeEmptyHeader)
{
lock (info)
{
// stuff
}
return true;
}
我们可以看到错误是由引起的info 为null。现在看看来电者：
We can see that the error would be cause by info to be null. Now looking at the caller:
internal virtual void AddHeaders(HttpHeaders sourceHeaders)
{
if (sourceHeaders.headerStore == null)
return;
List<string> stringList = (List<string>) null;
foreach (KeyValuePair<string, HttpHeaders.HeaderStoreItemInfo> keyValuePair in sourceHeaders.headerStore)
{
if (this.headerStore == null || !this.headerStore.ContainsKey(keyValuePair.Key))
{
HttpHeaders.HeaderStoreItemInfo headerStoreItemInfo = keyValuePair.Value;
if (!sourceHeaders.ParseRawHeaderValues(keyValuePair.Key, headerStoreItemInfo, false))
{
if (stringList == null)
stringList = new List<string>();
stringList.Add(keyValuePair.Key);
}
else
this.AddHeaderInfo(keyValuePair.Key, headerStoreItemInfo);
}
}
if (stringList == null)
return;
foreach (string key in stringList)
sourceHeaders.headerStore.Remove(key);
}
长话短说，我们在 DefaultRequestHeaders中迭代字典（即 sourceHeaders.headerStore ）并将标题复制到请求中。
Long story short, we iterate the dictionary in DefaultRequestHeaders (that's sourceHeaders.headerStore) and copy the headers into the request.
汇总它，同时我们有一个线程迭代字典的内容，和另一个添加/删除元素。这可能会导致您看到的行为。
Summing it up, at the same time we have a thread iterating the contents of the dictionary, and another adding/removing elements. This can lead to the behavior you're seeing.
要解决此问题，您有两种解决方案：
To fix this, you have two solutions:
-
在静态构造函数中初始化
DefaultRequestHeaders，然后永远不要更改它：
Initialize
DefaultRequestHeadersin a static constructor, then never change it:
static AttributesBaseController
{
Client = new HttpClient(new HttpClientHandler { Proxy = null, UseProxy = false })
{
Timeout = TimeSpan.FromSeconds(double.Parse(WebConfigurationManager.AppSettings["httpTimeout"]))
};
Client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));
}
使用 SendAsync 使用您的自定义标题而不是 PutAsync ：
Use SendAsync with your custom headers instead of PutAsync:
var message = new HttpRequestMessage(HttpMethod.Put, new Uri(WebConfigurationManager.AppSettings["dossier"] + "api/dossier?clientId=" + clientId));
message.Headers.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));
using (var response = await Client.SendAsync(message))
{
// ...
}
只是为了好玩，一个小的复制品：
Just for fun, a small repro:
var client = new HttpClient();
client.DefaultRequestHeaders.Accept.Clear();
client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));
var storeField = typeof(HttpHeaders).GetField("headerStore", BindingFlags.Instance | BindingFlags.NonPublic);
FieldInfo valueField = null;
var store = (IEnumerable)storeField.GetValue(client.DefaultRequestHeaders);
foreach (var item in store)
{
valueField = item.GetType().GetField("value", BindingFlags.Instance | BindingFlags.NonPublic);
Console.WriteLine(valueField.GetValue(item));
}
for (int i = 0; i < 8; i++)
{
Task.Run(() =>
{
int iteration = 0;
while (true)
{
iteration++;
try
{
foreach (var item in store)
{
var value = valueField.GetValue(item);
if (value == null)
{
Console.WriteLine("Iteration {0}, value is null", iteration);
}
break;
}
client.DefaultRequestHeaders.Accept.Clear();
client.DefaultRequestHeaders.Accept.Add(new Net.Http.Headers.MediaTypeWithQualityHeaderValue("application/json"));
}
catch (Exception) { }
}
});
}
Console.ReadLine();
输出：
迭代137，值为空
重现问题可能需要几次尝试，因为线程在同时访问字典时会陷入无限循环（如果它发生在您的Web服务器上，ASP.NET将在超时后中止线程） ）。
Reproducing the issue may take a few tries because threads tend to get stuck in an infinite loop when accessing the dictionary concurrently (if it happens on your webserver, ASP.NET will abort the thread after the timeout elapses).
这篇关于在异步方法中使用时，HttpClient标头变为空的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！