打开SqlConnection时"句柄无效"错误

Question

此错误已经开始偶尔发生并且莫名其妙,特别是在连接到会话状态数据库时.这是错误:

   Exception type: COMException 
    Exception message: The handle is invalid. (Exception from HRESULT: 0x80070006 (E_HANDLE))
   at System.Runtime.InteropServices.Marshal.ThrowExceptionForHRInternal(Int32 errorCode, IntPtr errorInfo)
   at System.Data.ProviderBase.DbConnectionPool.TryGetConnection(DbConnection owningObject, UInt32 waitForMultipleObjectsTimeout, Boolean allowCreate, Boolean onlyOneCheckConnection, DbConnectionOptions userOptions, DbConnectionInternal& connection)
   at System.Data.ProviderBase.DbConnectionPool.TryGetConnection(DbConnection owningObject, TaskCompletionSource`1 retry, DbConnectionOptions userOptions, DbConnectionInternal& connection)
   at System.Data.ProviderBase.DbConnectionFactory.TryGetConnection(DbConnection owningConnection, TaskCompletionSource`1 retry, DbConnectionOptions userOptions, DbConnectionInternal oldConnection, DbConnectionInternal& connection)
   at System.Data.ProviderBase.DbConnectionInternal.TryOpenConnectionInternal(DbConnection outerConnection, DbConnectionFactory connectionFactory, TaskCompletionSource`1 retry, DbConnectionOptions userOptions)
   at System.Data.SqlClient.SqlConnection.TryOpenInner(TaskCompletionSource`1 retry)
   at System.Data.SqlClient.SqlConnection.TryOpen(TaskCompletionSource`1 retry)
   at System.Data.SqlClient.SqlConnection.Open()

在Windows事件查看器中有时会出现可能相关的错误:

Application: w3wp.exe
Framework Version: v4.0.30319
Description: The process was terminated due to an unhandled exception.
Exception Info: System.Threading.SemaphoreFullException
Stack:
   at System.Threading.Semaphore.Release(Int32)
   at System.Data.ProviderBase.DbConnectionPool.CleanupCallback(System.Object)
   at System.Threading.ExecutionContext.RunInternal(System.Threading.ExecutionContext, System.Threading.ContextCallback, System.Object, Boolean)
   at System.Threading.ExecutionContext.Run(System.Threading.ExecutionContext, System.Threading.ContextCallback, System.Object, Boolean)
   at System.Threading.TimerQueueTimer.CallCallback()
   at System.Threading.TimerQueueTimer.Fire()
   at System.Threading.TimerQueue.FireNextTimers()

编辑:另一种例外情况如下:

Exception Type: System.ComponentModel.Win32Exception
Error message: An operation was attempted on something that is not a socket
No Stack Trace Available
Exception Type: System.Data.SqlClient.SqlException
Error message: A transport-level error has occurred when sending the request to the server. (provider: TCP Provider, error: 0 - An operation was attempted on something that is not a socket.)
at System.Data.SqlClient.TdsParser.TdsExecuteRPC(_SqlRPC[] rpcArray, Int32 timeout, Boolean inSchema, SqlNotificationRequest notificationRequest, TdsParserStateObject stateObj, Boolean isCommandProc, Boolean sync, TaskCompletionSource`1 completion, Int32 startRpc, Int32 startParam)
at System.Data.SqlClient.SqlCommand.RunExecuteReaderTds(CommandBehavior cmdBehavior, RunBehavior runBehavior, Boolean returnStream, Boolean async, Int32 timeout, Task& task, Boolean asyncWrite, SqlDataReader ds)
at System.Data.SqlClient.SqlCommand.RunExecuteReader(CommandBehavior cmdBehavior, RunBehavior runBehavior, Boolean returnStream, String method, TaskCompletionSource`1 completion, Int32 timeout, Task& task, Boolean asyncWrite)
at System.Data.SqlClient.SqlCommand.RunExecuteReader(CommandBehavior cmdBehavior, RunBehavior runBehavior, Boolean returnStream, String method)
at System.Data.SqlClient.SqlCommand.ExecuteReader(CommandBehavior behavior, String method)
at System.Data.SqlClient.SqlCommand.ExecuteReader(CommandBehavior behavior)
at System.Web.SessionState.SqlSessionStateStore.SqlExecuteReaderWithRetry(SqlCommand cmd, CommandBehavior cmdBehavior)
Exception Type: System.Web.HttpException
Error message: Unable to connect to SQL Server session database.
at System.Web.SessionState.SqlSessionStateStore.SqlExecuteReaderWithRetry(SqlCommand cmd, CommandBehavior cmdBehavior)
at System.Web.SessionState.SqlSessionStateStore.DoGet(HttpContext context, String id, Boolean getExclusive, Boolean& locked, TimeSpan& lockAge, Object& lockId, SessionStateActions& actionFlags)
at System.Web.SessionState.SqlSessionStateStore.GetItem(HttpContext context, String id, Boolean& locked, TimeSpan& lockAge, Object& lockId, SessionStateActions& actionFlags)
at System.Web.SessionState.SessionStateModule.GetSessionStateItem()
at System.Web.SessionState.SessionStateModule.BeginAcquireState(Object source, EventArgs e, AsyncCallback cb, Object extraData)
at System.Web.HttpApplication.AsyncEventExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute()
at System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously)

谁能建议:

1. 这是什么意思？
2. 是什么导致这种情况(这是一个非常稳定地运行了很长时间的应用程序,在此之前没有发生重大的基础设施变化)？
3. 可以做些什么来解决它？

Answer 1

事实证明,我们将错误跟踪到使用Json.Net反序列化CancellationToken.

当代码仍在尝试使用已释放的OS句柄时,会出现潜在的问题.当然,当您的代码直接使用句柄时,就会发生这种情况.我们的代码没有这样做,但事实证明,这可能发生在Json.Net上.这是如何做:

我们有一个课程如下:

public class MyClass
{
   ...
}

// in one part of the code, this class was serialized & deserialized using Json.Net:
JsonConvert.SerializeObject(...);
JsonConvert.DeserializeObject<MyClass>(...);

有人向MyClass添加了一个CancellationToken类型的属性时出现问题:

public class MyClass
{
    ...
    public CancellationToken Token { get; set; }
}

这是问题所在.序列化时,CancellationToken如下所示:

{"IsCancellationRequested":false,"CanBeCanceled":true,"WaitHandle":{"Handle":{"value":1508},"SafeWaitHandle":{"IsInvalid":false,"IsClosed":false}}}

注意,这样做是懒惰的 - 创建令牌的WaitHandle属性,并序列化其底层OS句柄的值(1508).

当我们反序列化令牌时,Json.Net将以new CancellationToken()(相当于CancellationToken.None)开头.然后,它将使用保存的值继续填充该Handle令牌的属性.这使得事情出错的一个显而易见的方法是默认的CancellationToken的WaitHandle现在指向一个可能无效的句柄.但是,更大的问题是更新句柄会取消引用WaitHandle的原始SafeHandle,从而允许垃圾收集器运行其终结器并进行清理.然后,您可以成为以下一系列事件的受害者:WaitHandleIntPtr

1. 句柄123被分配给池化数据库连接
2. 反序列化将句柄123分配给默认取消令牌的WaitHandle
3. 第二次反序列化将新句柄值分配给默认取消令牌的WaitHandle
4. 垃圾收集器运行并最终确定已释放的123安全句柄值
5. 数据库连接现在指向无效句柄

以下是一些使用以下方法故意复制问题的代码FileStream:

// serialize 2 tokens
var source = new CancellationTokenSource();
var serialized = JsonConvert.SerializeObject(source.Token);
var serialized2 = JsonConvert.SerializeObject(new CancellationTokenSource().Token);
var handle = source.Token.WaitHandle.Handle;
source.Dispose(); // releases source's handle

// spin until the OS gives us back that same handle as
// a file handle
FileStream fileStream;
while (true)
{
    fileStream = new FileStream(Path.GetTempFileName(), FileMode.OpenOrCreate);
    if (fileStream.Handle == handle) { break; }
}

// deserialize both tokens, thus releasing the conflicting handle
var deserialized = JsonConvert.DeserializeObject<CancellationToken>(serialized);
var deserialized2 = JsonConvert.DeserializeObject<CancellationToken>(serialized2);

GC.Collect();
GC.WaitForPendingFinalizers();

fileStream.WriteByte(1);
fileStream.Flush(); // fails with IOException "The handle is invalid"

Answer 2

在搜索答案一段时间后，没有成功，唯一解决此错误的是iisreset。