Disable GC entirely

[Manu]

On 7 April 2013 20:59, Paulo Pinto <pjmlp at progtools.org> wrote:

> I am not giving up speed. It just happens that I have been coding since
> 1986 and I am a polyglot programmer that started doing system programming
> in the Pascal family of languages, before moving into C and C++ land.
>
> Except for some cases, it does not matter if you get an answer in 1s or
> 2ms, however most single language C and C++ developers care about the 2ms
> case even before starting to code, this is what I don't approve.
>

Bear in mind, most remaining C/C++ programmers are realtime programmers,
and that 2ms is 12.5% of the ENTIRE AMOUNT OF TIME that you have to run
realtime software.
If I chose not to care about 2ms only 8 times, I'll have no time left. I
would cut off my left nut for 2ms most working days!
I typically measure execution times in 10s of microseconds, if something
measures in milliseconds it's a catastrophe that needs to be urgently
addressed... and you're correct, as a C/C++ programmer, I DO design with
consideration for sub-ms execution times before I write a single line of
code.
Consequently, I have seen the GC burn well into the ms on occasion, and as
such, it is completely unacceptable in realtime software.

The GC really needs to be addressed in terms of performance; it can't stop
the world for milliseconds at a time. I'd be happy to give it ~150us every
16ms, but NOT 2ms every 200ms.
Alternatively, some urgency needs to be invested in tools to help
programmers track accidental GC allocations.

I cope with D in realtime software by carefully avoiding excess GC usage,
which, sadly, means basically avoiding the standard library at all costs.
People use concatenations all through the std lib, in the strangest places,
I just can't trust it at all anymore.
I found a weird one just a couple of days ago in the function
toUpperInPlace() (!! it allocates !!), but only when it encountered a utf8
sequence, which means I didn't even notice while working in my language! >_<
Imagine it, I would have gotten a bug like "game runs slow in russian", and
I would have been SOOOO "what the ****!?", while crunching to ship the
product...

That isn't so say I don't appreciate the idea of the GC if it was efficient
enough for me to use. I do use it, but very carefully. If there are only a
few GC allocations it's okay at the moment, but I almost always run into
trouble when I call virtually any std library function within loops. That's
the critical danger in my experience.

Walter's claim is that D's inefficient GC is mitigated by the fact that D
produces less garbage than other languages, and this is true to an extent.
But given that is the case, to be reliable, it is of critical importance
that:
a) the programmer is aware of every allocation they are making, they can't
be hidden inside benign looking library calls like toUpperInPlace.
b) all allocations should be deliberate.
c) helpful messages/debugging features need to be available to track where
allocations are coming from. standardised statistical output would be most
helpful.
d) alternatives need to be available for the functions that allocate by
nature, or an option for user-supplied allocators, like STL, so one can
allocate from a pool instead.
e) D is not very good at reducing localised allocations to the stack, this
needs some attention. (array initialisation is particularly dangerous)
f) the GC could do with budgeting controls. I'd like to assign it 150us per
16ms, and it would defer excess workload to later frames.

Of course I think given time D compilers will be able to achieve C++ like
> performance, even with GC or who knows, a reference counted version.
>
> Nowadays the only place I do manual memory management is when writing
> Assembly code.
>

Apparently you don't write realtime software. I get so frustrated on this
forum by how few people care about realtime software, or any architecture
other than x86 (no offense to you personally, it's a general observation).
Have you ever noticed how smooth and slick the iPhone UI feels? It runs at
60hz and doesn't miss a beat. It wouldn't work in D.
Video games can't stutter, audio/video processing can't stutter. These are
all important tasks in modern computing.
The vast majority of personal computers in the world today are in peoples
pockets running relatively weak ARM processors, and virtually every user of
these devices appreciates the smooth operation of the devices interfaces.
People tend to complain when their device is locking up or stuttering.
These small, weak devices are increasingly becoming responsible for _most_
personal computing tasks these days, and apart from the web, most personal
computing tasks are realtime in some way (music/video, skype, etc).
It's not a small industry. It is, perhaps, the largest computing industry,
and sadly D is yet not generally deployable to the average engineer... only
the D enthusiast prepared to take the time to hold it's hand until this is
important issue is addressed.
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