未处理的异常会绕过 try/catch 块吗？

Question

I've this error, which occurs on a webapi I build:

An unhandled exception occurred and the process was terminated.

Application ID: /LM/W3SVC/1/ROOT/MyWebAPI

Process ID: 43144

Exception: IBM.Data.DB2.iSeries.iDB2SQLErrorException

Message: SQ20377 Character X'  3F' cannot be mapped to a valid XML character.

StackTrace:    at IBM.Data.DB2.iSeries.iDB2Exception.throwDcException(MpDcErrorInfo mpEI, MPConnection conn)
   at IBM.Data.DB2.iSeries.iDB2Command.reportDCError(Int32 rc)
   at IBM.Data.DB2.iSeries.iDB2Command.fetch()
   at IBM.Data.DB2.iSeries.iDB2DataReader.MPDataReader.FetchData(UInt32& rowsReturned, UInt32& blockNumber)
   at IBM.Data.DB2.iSeries.iDB2DataReader.MPDataReader.FetchThread()
   at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
   at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
   at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
   at System.Threading.ThreadHelper.ThreadStart()

Every query to DB2 are catched, so any error should be logged and managed. But instead, "sometimes" (not always) the whole application pool go down due to these errors.

I said sometimes because some of those errors on Event Viewers (which are the same) are logged, but don't stop the IIS pool.

Its running .NET v4.0.

What can it be? Can a try/catch be bypassed? Very weird...

EDIT:

most try/catch are generic:

try
{

}
catch (Exception ex)
{

}

some are specifics, such as:

int rowCount = 0;
SqlBuilder.Template template = null;

try
{
    template = CreateSQLTemplate(filters, "rowcount");

    using (iDB2Connection db2 = new iDB2Connection(Properties.Settings.Default.AS400Connection))
    {
        var rowCounts = db2.Query<int>(template.RawSql, template.Parameters);
        rowCount = rowCounts.Count() > 0 ? rowCounts.First() : 0;
    }
}
catch(iDB2SQLErrorException db2Sqlex)
{
    //
}
catch (Exception ex)
{
    //
}

This can be enough, can't be?

Answer 1

You try set EnablePreFetch=false in connection string?

https://www.ibm.com/mysupport/s/question/0D50z000060GNJx/threading-issue?language=en_US

https://social.msdn.microsoft.com/Forums/vstudio/en-US/8f487219-22ad-48cc-b743-aa15c8d7dd4f/threading-exception?forum=clr

Answer 2

The .NET Framework provides a couple events that can be used to catch unhandled exceptions. You only need to register for these events once in your code when your application starts up. For ASP.NET, you would do this in the Startup class or Global.asax

static void Application_ThreadException(object sender, ThreadExceptionEventArgs e)
{
     // Log the exception, display it, etc
     Debug.WriteLine(e.Exception.Message);
}

static void CurrentDomain_UnhandledException(object sender, UnhandledExceptionEventArgs e)
{
     // Log the exception, display it, etc
     Debug.WriteLine((e.ExceptionObject as Exception).Message);
}

Answer 3

Do you have tried to subscribe to this event? TaskScheduler.UnobservedTaskException Event

This behavior is changed since .NET framework 4.5 but you can enable it to have maybe more details for the origin of this exception.

The event is a static one, it's recommended to subscribe to this event as soon as possible at the start of your application.

Don't miss editing the configuration file

<runtime>
    <ThrowUnobservedTaskExceptions enabled="true"/>
</runtime>

This an example of use tpl-exception-handling

Notice this also Release mode

Hope this helps

Answer 4

Try turning on connection pooling in your DB connection:

var connb = new DB2ConnectionStringBuilder(ConfigurationManager.ConnectionStrings["ConnectionString"].ConnectionString);
connb.Pooling = true;
connb.MinPoolSize = 1;
connb.MaxPoolSize = 100;
var conn = new DB2Connection(connb.ConnectionString);

If you can't or don't want to do that, make sure to explicitly close every single connection to the db after you're done with it. Otherwise an unhandled exception may be thrown when the garbage collector picks up your open connection objects. This problem has been observed before with the DB2 provider.

Answer 5

According to the stack trace, this exception happens in a thread that DB2 creates automatically. It doesn't run any of your code so you can't catch this exception with a try block.

1. Configure the Visual Studio debugger to break on unhandled exceptions.
2. Try to find out where that strange-looking character comes from. Those two blanks in front of the 3F look suspicious.