我不确定原因，但是当我在高负载下加载测试RavenDB进行并发写入时，我遇到以下异常：“集合已被修改;枚举操作可能无法执行。”
高负荷，我说每秒1000个请求，更新100个文件。为了对此进行一些上下文，我将使用RavenDB来记录MVC站点上的操作，并且我正在运行测试工具来调用log方法以查看它是否可以处理记录这么多事情。每个文档代表用户在网站上的会话中的操作。
如果有帮助，那么具有相同请求数的文档就会运行得很少。每秒请求数量相应较多的文档也较少也可以正常运行。
我从研究中看到，在线程之间共享IDocumentSession有时是负责任的，但我不相信我的代码会这样做。
这是相关的记录逻辑：
public class ActivityLogger : IActivityLogger
{
private static ActivityLogger _instance;
public static ActivityLogger Instance
{
get
{
if (_instance == null)
{
_instance = new ActivityLogger();
}
return _instance;
}
set { _instance = value; }
}
private static DocumentStore docStoreInstance;
// keeping this as a singleton - we only ever want one as it's expensive
private static DocumentStore DocumentStore
{
get
{
if (docStoreInstance == null)
{
docStoreInstance = new DocumentStore() {ConnectionStringName = "RavenLogging"};
docStoreInstance.Initialize();
}
return docStoreInstance;
}
}
...
/// <summary>
/// Logs the given LogItem to Raven, to the given UserSession
/// </summary>
public void Log(LogItem item, UserSession userSession)
{
if (userSession == null)
{
return;
}
if (!userSession.Activities.Contains(item))
{
userSession.Activities.Add(item);
if (Cache != null)
Cache.AddToSession(CachedObjects.USER_LOGGING_SESSION, userSession);
}
// done in a task since we don't want the app to wait for us to finish logging
Task.Factory.StartNew(() =>
{
using (var session = DocumentStore.OpenSession())
{
try
{
session.Store(userSession);
session.SaveChanges();
}
catch (Raven.Abstractions.Exceptions.ConcurrencyException ce)
{
if (ce.ExpectedETag != ce.ActualETag)
{
// the user session is stale, reload it and try again
userSession = session.Load<UserSession>(userSession.Id);
Log(item, userSession);
}
}
}
});
}
}
以下是我的测试工具中的代码
public void Begin()
{
startTime = DateTime.Now;
DateTime endTime = startTime.AddSeconds(Duration);
int itemsLoggedThisSecond, secondsRemaining = 0;
while (DateTime.Now < endTime)
{
// if we're still on the same second somehow, wait
if (endTime.Subtract(DateTime.Now).Seconds == secondsRemaining)
{
Thread.Sleep(10);
continue;
}
itemsLoggedThisSecond = 0;
while (itemsLoggedThisSecond < RequestsPerSecond)
{
int innerItemsLoggedThisSecond = itemsLoggedThisSecond;
Parallel.ForEach(Sessions, (session, state) =>
{
if (innerItemsLoggedThisSecond == RequestsPerSecond)
{
state.Break();
}
var item = MakeRandomLogItem();
ActivityLogger.Instance.Log(item, session);
if (!session.Activities.Contains(item))
{
session.Activities.Add(item);
}
innerItemsLoggedThisSecond++;
});
itemsLoggedThisSecond = innerItemsLoggedThisSecond;
}
secondsRemaining = (int) endTime.Subtract(DateTime.Now).TotalSeconds;
Console.Write("\r" + secondsRemaining + " seconds remaining ");
}
}
如果它有帮助，这是例外。
System.InvalidOperationException was unhandled by user code
HResult=-2146233079
Message=Collection was modified; enumeration operation may not execute.
Source=mscorlib
StackTrace:
at System.ThrowHelper.ThrowInvalidOperationException(ExceptionResource resource)
at System.Collections.Generic.List`1.Enumerator.MoveNextRare()
at System.Collections.Generic.List`1.Enumerator.MoveNext()
at Raven.Imports.Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.SerializeList(JsonWriter writer, IWrappedCollection values, JsonArrayContract contract, JsonProperty member, JsonContainerContract collectionContract, JsonProperty containerProperty) in c:\Builds\RavenDB-Stable\Imports\Newtonsoft.Json\Src\Newtonsoft.Json\Serialization\JsonSerializerInternalWriter.cs:line 524
at Raven.Imports.Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.SerializeValue(JsonWriter writer, Object value, JsonContract valueContract, JsonProperty member, JsonContainerContract containerContract, JsonProperty containerProperty) in c:\Builds\RavenDB-Stable\Imports\Newtonsoft.Json\Src\Newtonsoft.Json\Serialization\JsonSerializerInternalWriter.cs:line 129
at Raven.Imports.Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.SerializeObject(JsonWriter writer, Object value, JsonObjectContract contract, JsonProperty member, JsonContainerContract collectionContract, JsonProperty containerProperty) in c:\Builds\RavenDB-Stable\Imports\Newtonsoft.Json\Src\Newtonsoft.Json\Serialization\JsonSerializerInternalWriter.cs:line 383
at Raven.Imports.Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.SerializeValue(JsonWriter writer, Object value, JsonContract valueContract, JsonProperty member, JsonContainerContract containerContract, JsonProperty containerProperty) in c:\Builds\RavenDB-Stable\Imports\Newtonsoft.Json\Src\Newtonsoft.Json\Serialization\JsonSerializerInternalWriter.cs:line 124
at Raven.Imports.Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.Serialize(JsonWriter jsonWriter, Object value) in c:\Builds\RavenDB-Stable\Imports\Newtonsoft.Json\Src\Newtonsoft.Json\Serialization\JsonSerializerInternalWriter.cs:line 62
at Raven.Imports.Newtonsoft.Json.JsonSerializer.SerializeInternal(JsonWriter jsonWriter, Object value) in c:\Builds\RavenDB-Stable\Imports\Newtonsoft.Json\Src\Newtonsoft.Json\JsonSerializer.cs:line 627
at Raven.Imports.Newtonsoft.Json.JsonSerializer.Serialize(JsonWriter jsonWriter, Object value) in c:\Builds\RavenDB-Stable\Imports\Newtonsoft.Json\Src\Newtonsoft.Json\JsonSerializer.cs:line 599
at Raven.Json.Linq.RavenJToken.FromObjectInternal(Object o, JsonSerializer jsonSerializer) in c:\Builds\RavenDB-Stable\Raven.Abstractions\Json\Linq\RavenJToken.cs:line 83
at Raven.Json.Linq.RavenJObject.FromObject(Object o, JsonSerializer jsonSerializer) in c:\Builds\RavenDB-Stable\Raven.Abstractions\Json\Linq\RavenJObject.cs:line 159
at Raven.Client.Document.EntityToJson.GetObjectAsJson(Object entity) in c:\Builds\RavenDB-Stable\Raven.Client.Lightweight\Document\EntityToJson.cs:line 74
at Raven.Client.Document.EntityToJson.ConvertEntityToJson(String key, Object entity, RavenJObject metadata) in c:\Builds\RavenDB-Stable\Raven.Client.Lightweight\Document\EntityToJson.cs:line 41
at Raven.Client.Document.InMemoryDocumentSessionOperations.EntityChanged(Object entity, DocumentMetadata documentMetadata) in c:\Builds\RavenDB-Stable\Raven.Client.Lightweight\Document\InMemoryDocumentSessionOperations.cs:line 1033
at Raven.Client.Document.InMemoryDocumentSessionOperations.<PrepareForEntitiesPuts>b__14(KeyValuePair`2 pair) in c:\Builds\RavenDB-Stable\Raven.Client.Lightweight\Document\InMemoryDocumentSessionOperations.cs:line 908
at System.Linq.Enumerable.WhereEnumerableIterator`1.MoveNext()
at System.Linq.Buffer`1..ctor(IEnumerable`1 source)
at System.Linq.Enumerable.ToArray[TSource](IEnumerable`1 source)
at Raven.Client.Document.InMemoryDocumentSessionOperations.PrepareForEntitiesPuts(SaveChangesData result) in c:\Builds\RavenDB-Stable\Raven.Client.Lightweight\Document\InMemoryDocumentSessionOperations.cs:line 908
at Raven.Client.Document.InMemoryDocumentSessionOperations.PrepareForSaveChanges() in c:\Builds\RavenDB-Stable\Raven.Client.Lightweight\Document\InMemoryDocumentSessionOperations.cs:line 901
at Raven.Client.Document.DocumentSession.SaveChanges() in c:\Builds\RavenDB-Stable\Raven.Client.Lightweight\Document\DocumentSession.cs:line 694
at Pendragon.Infrastructure.ActivityLogger.<>c__DisplayClass2.<Log>b__1() in c:\Users\me\repos\project\project\Infrastructure\Logger.cs:line 103
at System.Threading.Tasks.Task.InnerInvoke()
at System.Threading.Tasks.Task.Execute()
我这里没有任何线索，所以任何帮助都表示感谢。
答案 0 :(得分：1)
在某个级别，一个线程正在枚举一个集合，然后另一个线程会更改该集合。简而言之，ActivityLogger.Instance不是线程安全的。
至少每个线程我会有一个乌鸦连接。您可以考虑不共享连接，并且每个请求都有一个连接，特别是因为您在托管时将获得一个MVCController，因此这将提供更准确的压力测试。
简单的解决方案可能是松开单ActivityLogger.Instance并在Parallel.ForEach内创建一个新的。即。
ActivityLogger.Instance.Log(item, session);
变为：
new ActivityLogger().Log(item, session);
（假设没有其他单身人士在场？）