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Date: Tue, 8 Mar 2005 07:47:55 +0100 (CET)
From: "David Bertoni (JIRA)" <xerces-c-dev@xml.apache.org>
To: xerces-c-dev@xml.apache.org
Subject: [jira] Commented: (XERCESC-1368) Catch-all handler are problematic on
 Windows
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     [ http://issues.apache.org/jira/browse/XERCESC-1368?page=comments#action_60407 ]
     
David Bertoni commented on XERCESC-1368:
----------------------------------------

First of all, I think you are misinterpreting what I'm saying.  I'm not proposing Xerces-C should add any platform-specific code, or some make some decision about how an application handles exceptions.

What I'm saying is Xerces-C as a library should:

1. Catch the exceptions it knows about and avoid gratuitously catching exceptions it doesn't.

2. As a result of 1, it should avoid using catch-all handlers solely for the purpose of releasing an acquired resource.  This is better handled through RAII (resource allocation is initialization).

3. Neve use a catch-all handler that doesn't re-throw the exception that was caught.  This actually happens in many places.

I really think this will lead to a library which is more portable.  It will certainly lead to a library which has cleaner code.

> Catch-all handler are problematic on Windows
> --------------------------------------------
>
>          Key: XERCESC-1368
>          URL: http://issues.apache.org/jira/browse/XERCESC-1368
>      Project: Xerces-C++
>         Type: Bug
>   Components: Miscellaneous
>     Versions: 2.6.0
>  Environment: Windows XP with Visual Studio .NET 2003
>     Reporter: David Bertoni

>
> Exception handlers of the form "catch(...)" are causing problems in our product code on Windows, because they are catching hardware exceptions, such as access violations.
> There is an article in the MSDN Knowledge Base that describes how this has changed between Visual Studio 6, and Visual Studio .NET:
> http://msdn.microsoft.com/library/default.asp?url=/library/en-us/vclang/html/_core_exception_handling.3a_.default_synchronous_exception_model.asp
> However, my experience with Xerces-C using Visual Studio .NET 2003 is that hardware exceptions (asynchronous exceptions, in the Microsoft parlance) are still being caught in Xerces-C in catch-all handlers.  This is problematic because it interferes with normal diagnosis of hardware faults, and can lead to code being executed in Xerces-C when the system is in an unknown state.  It is also a makes it difficult to write code that will behave the same on other platforms.
> Looking into the code reveals multiple places where a catch-all handler resets some object (or some other similar behavior), then rethrows the same exception.  I'd like to propose that we try to eliminate as many of these catch handlers as possible by replaces these actions with stack objects that perform these actions automatically whether or not an exception is thrown (auto_ptr-like behavior).  This will also have the benefit of simplifying the code.  From a "philosophical" perspective, I also think its better for code to catch the exceptions it's concerned with, and avoid catch-all handlers except when absolutely necessary.
> I will attach a proposed patch for a class that does this sort of thing, and some modified code that uses this class.  I would also like to see if anyone else has observed this behavior in their Windows applications.

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