[Mono-list] Exceptions and error codes.

[Thong (Tum) Nguyen]

Hi Paolo,

It is an interesting point!  It seems like a good idea not to throw
exceptions from methods invoked by native code.

You can still throw exceptions before and after invoking native code
(outside of call-backs) so the problem doesn't affect the recommendation
I made that public methods in GTK# should throw exceptions rather than
use error codes ;-).

All the best,

^Tum

> -----Original Message-----
> From: mono-list-admin@lists.ximian.com [mailto:mono-list-
> admin@lists.ximian.com] On Behalf Of Paolo Molaro
> Sent: Wednesday, 26 March 2003 12:30 a.m.
> To: mono-list@lists.ximian.com
> Subject: Re: [Mono-list] Exceptions and error codes.
> 
> On 03/21/03 Thong (Tum) Nguyen wrote:
> > > You make some good arguments, but I think most of it is irrelevant
> > > since, in order to remain compatible with .NET, Mono must behave
the
> > > same way with respect to returning (or not) exceptions. The MSDN
docs
> > > describe exactly what exceptions/return codes File.Exists and
> > File.Open
> > > should return, Mono should do the same (unless the docs are in
error).
> > A
> > > lot of work has already been done on this. You'll notice that many
of
> > > the test cases test whether or not the correct exception is being
> > > returned.
> >
> >
> > Definitely.  I was more referring to our own class libraries (such
as
> > GTK#).
> 
> I just want to add another data point to the ones already explained
> about the use of error codes or exceptions, especially as it relates
to
> Gtk+, but this also applies to other libraries that are P/invoked from
> the CLR.
> C code has no notions of exceptions and of the way exception handling
> can unwind the stack (yes, on windows people use SEH in C code, but
it's
> non-standard and I don't even know if the MS CLR deals with SEH in C
> code). So what may happen is:
> 
> 	C# code with a try block
> 	-> Gtk+ code (takes a lock and calls a delegate)
> 	-> C# code that trows an exception
> 	-> exceptions handling triggers and gets the stack back to the
try
> block
> 	-> next time Gtk+ is called again and it needs the lock (that
> 	could be not unlocked by the exception code, since it's not
> 	aware of it) you get a nice deadlock
> 
> lupus
> 
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