[openbeos] Re: C++ in the kernel
- From: "Axel Dörfler" <axeld@xxxxxxxxxxxxxxxx>
- To: openbeos@xxxxxxxxxxxxx
- Date: Sun, 23 Feb 2003 19:37:42 +0100 CET
"Michael Phipps" <mphipps1@xxxxxxxxxxxxxxxx> wrote:
> Exceptions (in C++) are not a really good paradigm for kernel work
> anyway, unless you have a completely C++ kernel. Why, you may ask?
Well, let me share an experience from VM2.
> I am using exceptions in VM2, WHILE IT IS IN USER LAND, to emulate
> signal handling.
> I recently ran into a situation where the whole VM hung with no
> explanation. It turned out that I had a semaphore locked and threw an
exception. When another thread tried to run, it was completely blocked.
>
> The solution is one of:
> 1) A "finally" clause, like in Java, where no matter what code path
> occurs, exception or not, certain things happen.
> 2) A constructed class (like a BAutoLocker) that will go out of scope
> when the exception occurs
> 3) Don't use exceptions
> 4) Replicate all of the "normal exit" code before throwing.
>
> 1 isn't an option. 2 could be done. 3 was my final choice and 4 was
> my interim solution.
Yes, I agree, 3) does fine for me :-)
> >Virtuals are possible - just RTTI needs some bits from the C++ link
> >library that you would have to implement yourself. Of course, that
> >would make the kernel dependent on a specific compiler version which
> > we
> >want to avoid for the time being.
> Yes. Also the performance issues.
There is no real performance issue - for most compilers (incl. gcc)
it's just a matter of dereferencing a pointer (and compare that value
to another :).
> >> - STL: not sure why
> >Only because it uses features that need aren't provided in the
> > kernel C
> >++ runtime library. But it's possible to find your way around it, as
> >outlined above.
> STL has potential to be a performance issue. This is not a criticism
> of it, as such,
> but STL makes it very easy to do bad (slow) things. It also makes
> doing good
> things easier.
Yes, I would also not recommend to use the STL in the kernel (too much
of a big thing ;-)).
> Templates. Hmph. :-)
Templates are a great way to overcome the OO limitations of C++ :-)
Adios...
Axel.
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