[jira] Commented: (XERCESC-1368) Catch-all handler are problematic on Windows

["Michael Fuller (JIRA)" <xe...@xml.apache.org>]

     [ http://issues.apache.org/jira/browse/XERCESC-1368?page=comments#action_60399 ]
     
Michael Fuller commented on XERCESC-1368:
-----------------------------------------

We've run into this issue elsewhere in code we maintain.  We too make
extensive use of catch(...).

Under Unix, this isn't an issue because segmentation faults, div. by
zero, etc.  get turned into signals.  If an application wants to try
to cope with these faults, it should set up the appropriate signal
handler.

Under Windows, they get turned into pseudo-exceptions.  The right way
to cope with these pseudo-exceptions is to use a vectored exception handler.
An application that cares about DIV0, SEGV, etc. should set up a
vectored exception handler:
  http://msdn.microsoft.com/library/default.asp?url=/library/en-us/debug/base/vectoredhandler.asp

(For older versions of Windows, you have to use _set_se_translator()
instead.)

In either case, it's an application level decision how to cope with
SEGV, DIV0, etc.  Under Unix, you use a signal handler; or not.
Under Windows, you use a VectoredHandler; or not.
A library -- such as Xerces -- should *not* make that decision.
Any application that wants to can install a VectoredHandler;
The Xerces library shouldn't take that decision away from the
application developer.

I suggest we should close this issue as a "not broken, won't fix".

Michael

> 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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