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Re: [4diac-dev] Migrating forte to +11
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Hi Alois,
On 10.06.20 21:02, Alois Zoitl wrote:
I have rather mixed feelings here. At first I see the cool features of modern C++ (e.g., lambdas, const expr) which can help to improve code quality and flash
size.
Also think of more limited devices that cannot run forte yet (Cortex-M
with 128k flash?). With these features, it would become easier to
address such resource-constrained devices. Lots of compile-time
optimisation beyond constexpr, much better control over memory through
polymorphic memory resources. std::string with short string
optimisation, the list of useful features is long.
Also think of security: Programming according to the C++ Core Guidelines
will go a long way to eliminate accidental memory errors -- although
forte does not show any obvious flaws in this area, it hasn't been
audited or penetration-tested, or has it?
However I also see that we have a very diverse community with many different OSes (e.g., I hear that ThreadX is coming back via some Microsoft initiative),
different CPUs and memory capacity. While I thought most of our hardware will be arm and Linux based by now it looks not like that will come. Also RAM is still
a crucial thing in many devices of our users. Just have a look at the current discussion in the forum.
I would expect RAM usage to be lower with C++11 or later. But rare
platforms are a problem indeed.
Unlike the current cross-platform approach, I don't see an easy way to
use C++11/14/17 features in a way that allows fallback implementations
for platforms that don't have full library support for C++11 -- for
example, there's a big difference between using constexpr and
std::thread on FreeRTOS. I'd expect the former to be Just Working, the
latter to require explicit FreeRTOS support in the standard library.
On the other hand, we already need C++ support. My experience is that
people resist C++ on exotic platforms because of the misconception that
it is inefficient or bloated, but we are already beyond that. Getting
C++11 support as an upgrade should be much easier than getting C++
support in the first place. Generically speaking, I think it is
reasonable to require support for an almost 10 year old standard. We're
not the only ones who want to use modern C++.
As for C++ beyond 11, there is https://abseil.io, which maps C++14/17
features to 11 if the compiler doesn't support the newer versions, and
uses the native implementation if it does. That might be a pragmatic
compromise.
We should probably begin by checking all platforms that forte officially
supports. Do we even have access to all of them, or are some of them
orphaned? We should maybe also explicitly ask users on which kind of
systems they use forte, so we can discover exotic platforms we happen to
support without knowing it.
Therefore, in order to not limit the applicability of 4diac FORTE I think we should proceed here with great caution. Also I don't think we should spend our
limited resources on the transformation because of transformation. Especially because of our great set of test case. Thanks to all who worked on that.
I agree that if we do this step (which I really hope to become true), we
should be fully aware what we break, that there are upgrade options for
all users, and that these options are reasonable.
There are places where I see some immediate benefits (e.g., replacing our single linked list with STL vector), which can reduce our memory usage further. But it
would need some experiments to see if STL is not bringing other drawbacks regarding memory (e.g., memory blocked by support functions).
When talking about the big three (gcc, clang, Microsoft), using library
features are highly likely to be better than a hand-coded solution.
Regarding STL vector, polymorphic memory resources are very interesting
for memory-constrained platforms (std::pmr:vector). That is a C++17
feature, however.
Regards,
--
Dipl.-Inform. Jörg Walter
Senior Researcher
R&D Group Distributed Computation and Communication
OFFIS e.V. - Institut für Informatik
FuE Bereich Produktion | R&D Division Manufacturing
Escherweg 2, 26121 Oldenburg - Germany
Phone/Fax.: +49 441 9722-729 / -282
E-Mail: joerg.walter@xxxxxxxx
URL: http://www.offis.de
Registergericht: Amtsgericht Oldenburg VR 1956
Vorstand: Prof. Dr.-Ing. Wolfgang H. Nebel (Vorsitzender),
Prof. Dr. techn. Susanne Boll-Westermann, Prof. Dr.-Ing. Axel Hahn,
Prof. Dr.-Ing. Andreas Hein, Prof. Dr. Sebastian Lehnhoff
