Re: ThreadPool - C# Discussion Boards

27-Apr-08 19:40

Hello everyone,

Two simple questions about C# threadpool.

1. C# CLR only has one thread pool per process, means the asynchronous method call (implicit using thread pool) and the explicit using thread pool by ThreadPool.QueueUserWorkItem will share the same thread pool?

2. For the exceptions occured in asynchronous method call, when we call EndInvoke, if exception is thrown and we can catch the exception. But when we use the the thread pool explicitly by ThreadPool.QueueUserWorkItem, we can not catch any exception occured?

thanks in advance,
George

Zoltan Balazs27-Apr-08 21:48

27-Apr-08 21:48

These are not simple questions Wink | ;)

1. using directly the ThreadPool by QueueUserWorkItem or indirectly by asynchronous methods will share the same thread pool.
2. In .NET 2.0 any unhandled exception on any thread shuts down the application (see here[^])
The solution is to
- use a try/catch block in every thread entry method (in order to avoid application shutdown in case of an unhandled exception)
- or use the application domain AppDomain.UnhandledException event.

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George_George27-Apr-08 23:30

27-Apr-08 23:30

Thanks Zoltan,

I have read the link, looks cool! One simple question, what means "The common language runtime or a host process terminates the thread by throwing an internal exception." Could you show me a sample please?

regards,
George

Zoltan Balazs28-Apr-08 1:29

28-Apr-08 1:29

It means that if the thread method does not contain a try/catch block the application will be terminated.
Example (try it with/without the try/catch)

public static void Main()
{
    new Thread(TestMethod).Start();
}

static void TestMethod()
{
    int i=0;
    double result;

    try { result = 100/i; }
    catch (DivideByZeroException exc)
    { Console.Write(exc.Message); }
}

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George_George28-Apr-08 1:43

28-Apr-08 1:43

Thanks Zoltan!

What means "internal exception"? Which exception in your sample is internal exception? (Is internal exception something that is CLR internal used exception type, which is not exposed?)

regards,
George

Zoltan Balazs28-Apr-08 2:49

28-Apr-08 2:49

The DivideByZero is the internal exception. I guess the term internal means in this context that the exception will be one of the type derived from System.Exception.

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George_George28-Apr-08 3:50

28-Apr-08 3:50

Thanks Zoltan,

I read the documents you referred before again, there is a statement "provides a backstop for certain unhandled exceptions", backstop means?

regards,
George

Zoltan Balazs28-Apr-08 4:29

28-Apr-08 4:29

google it![^]
You don't need to understand each word in a documentation. Try to understand the principles and the rest will follow in time.

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George_George28-Apr-08 4:51

28-Apr-08 4:51

Thanks Zoltan,

I understand what is the meaning of backstop in English. But I do not understand what means "provides a backstop for certain unhandled exceptions" in the context. Does it mean for the scenarios listed in the MSDN page, CLR will prevent process will termination by a backstop? I do not think so, I have tested uncaught exception will cause process terminated. So, what makes me confused is what means "provides a backstop for certain unhandled exceptions". Smile | :)

Any ideas?

--------------------
- A ThreadAbortException is thrown in a thread because Abort was called.

- An AppDomainUnloadedException is thrown in a thread because the application domain in which the thread is executing is being unloaded.

- The common language runtime or a host process terminates the thread by throwing an internal exception.
--------------------

regards,
George

Zoltan Balazs28-Apr-08 4:58

28-Apr-08 4:58

Follow the text:
"If any of these exceptions are unhandled in threads created by the common language runtime, the exception terminates the thread, but the common language runtime does not allow the exception to proceed further."
So it's exactly what is said there: backstop meaning that the application will be terminated.

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George_George29-Apr-08 1:31

29-Apr-08 1:31

Thanks Zoltan,

I have made some self-tests and I want to confirm with you that (sorry for my bad English), "the application will be terminated" means process termination because of unhandled exception from a thread?

regards,
George

Zoltan Balazs29-Apr-08 1:47

29-Apr-08 1:47

It means process termination if you prefer that way, with an error dialog showing up. You know! Wink | ;)

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George_George29-Apr-08 2:13