Exception handling: Is finally executed after throw?

Question

Assume you have the following code:

Instead of doing:

Try
    '
    ' Initialize some objects
    '

    '
    ' do something that fails
    '

    '
    ' Clean up-code that gets not reached because exception
    '
Catch e As Exception
    '
    'Clean up initialized objects
    '

    Throw e
End Try

I would like to do:

Try
    '
    ' Initialize some objects
    '

    '
    ' do something that fails
    '
Catch e As Exception
    Throw e
Finally
    '
    'Clean up initialized objects
    '
End Try

So my simple question is: In case of an exception is the finally block reached even if there is a throw some lines before?

[EDIT] Thanks for your fast answers.

In first line there will be NullReference-, COM- and FileNotFound-Exceptions I think.

Ok, I will go for this code:

Try
    '
    ' Initialize some objects
    '

    '
    ' do something that fails
    '
Catch e As Exception      ' or just "Catch"??        
    Throw
Finally
    '
    'Clean up initialized objects
    '
End Try

All the best!

Inno

Answer 1

So my simple question is: In case of an exception is the finally block reached even if there is a throw some lines before?

Yes. The Finally block is always¹⁾ executed and exists precisely for clean-up. In your code, remove the Catch block, it does nothing. Worse, it actually destroys the stack trace because you don’t re-throw the original exception, you throw a new one.

If you really need a Catch block that then re-throws the exception, use the following:

Catch e As XyzException
    ' … do some stuff. '
    Throw
End Try

---

¹⁾: Caveat emptor: there are some exceptions such as StackOverflowException (how fitting …) which require special attention and may not trigger the Finally block. Handling them correctly is usually quite difficult.

Answer 2

Yes it does, finally is executed in any case. (there are only few exceptions - Response.Redirect and some cases with multithreading)

Answer 3

No, it is NOT guaranteed to run. There are certain exceptions - for example StockOverflowException and OutOfMemoryException - where the execution of a finally block is not guaranteed.

Answer 4

In almost all cases, a Finally will execute in a Try/Catch block (notable exceptions including when a StackOverflowException or OutOfMemoryException occur). I am curious though, why you didn't try this out for yourself. A valuable way to learn things is to actually try them out for yourselves - after all, you could end up accepting an answer that is wrong or misleading, and you will labour under this falsehood from that point on.

Answer 5

NOTE: System.Environment.FastFail method was kill current process/thread immediatly, without execute finally sections.