这个错误已经开始偶尔发生，而且令人费解，特别是在连接到会话状态数据库时。错误如下：
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()
Windows事件查看器中有时会出现一个可能相关的错误：
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)
有人能建议：
这是什么意思？
什么原因会导致这种情况（这是在一个运行了很长一段时间非常稳定的应用程序中，在这种情况开始出现之前没有发生重大的基础设施更改）？
如何解决？
最佳答案：
事实证明，我们跟踪到了用json.net反序列化cancellationtoken的错误。
当代码仍在尝试使用已释放的操作系统句柄时，就会出现底层问题。当然，这可能发生在您的代码直接与句柄一起工作时。我们的代码不这样做，但事实证明，这可能发生在Json.Net身上。以下是如何：
我们上了一节课，内容如下：
public class MyClass
{
...
}
// in one part of the code, this class was serialized & deserialized using Json.Net:
JsonConvert.SerializeObject(...);
JsonConvert.DeserializeObject<MyClass>(...);
当有人将属性添加到类型为CancellationToken的MyClass时出现问题：
public class MyClass
{
...
public CancellationToken Token { get; set; }
}
这就是问题所在。序列化时，CancellationToken如下所示：
{"IsCancellationRequested":false,"CanBeCanceled":true,"WaitHandle":{"Handle":{"value":1508},"SafeWaitHandle":{"IsInvalid":false,"IsClosed":false}}}
注意，这样做会创建令牌的waithandle属性，并序列化其底层os handle（1508）的值。
当我们反序列化令牌时，json.net将以
new CancellationToken()CancellationToken.NoneHandleWaitHandle句柄123分配给池数据库连接
反序列化将句柄123分配给默认取消令牌的waithandle
第二次反序列化将新的句柄值分配给默认取消令牌的waithandle
垃圾收集器运行并完成释放的123安全句柄值
数据库连接现在指向一个无效的句柄
下面是一些代码，它们故意使用
IntPtr// 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"