John Carmack applauds D's pure attribute

foobar foo at
Sun Feb 26 23:43:58 PST 2012

On Monday, 27 February 2012 at 04:17:24 UTC, Andrew Wiley wrote:
> On Sun, Feb 26, 2012 at 11:05 AM, Paulo Pinto 
> <pjmlp at> wrote:
>> Am 26.02.2012 17:34, schrieb so:
>>> On Sunday, 26 February 2012 at 15:58:41 UTC, H. S. Teoh wrote:
>>>> Would this even be an issue on multicore systems where the 
>>>> GC can run
>>>> concurrently? As long as the stop-the-world parts are below 
>>>> some given
>>>> threshold.
>>> If it is possible to guarantee that i don't think anyone 
>>> would bother
>>> with manual MM.
>> Well, some game studios seem to be quite happy with XNA, which 
>> implies using
>> a GC:
> I don't really see why you keep bringing up these examples. 
> This is a
> performance issue, which means you can certainly ignore it and 
> things
> will still work, just not as well. I've seen 3d games in Java, 
> but
> they always suffer from an awkward pause at fairly regular 
> intervals.
> This is why the AAA shops are still writing most of the engines 
> in
> C++.
> You will always be able to find examples of developers that 
> simply
> chose to ignore the issue for one reason or another.
> To make it clear, I'm not trying to antagonize you here. I 
> agree that
> GC is in general a superior technical solution to manual memory
> management, and given the research going into GC technology, 
> I'm sure
> that long term it's probably a good idea.
> However, I disagree with your statement that "the main issue is 
> that
> the GC needs to be optimized, not that manual memory management 
> is
> required."
> Making a GC that can run fast enough to make this sort of thing 
> a
> non-issue is currently so hard that it can only be used in 
> certain
> niche situations. That will probably change, but it will 
> probably
> change over the course of several years. Manual memory 
> management,
> however, is here now and dead simple to use so long as the 
> programmer
> understands the semantics. Programming in that model is harder, 
> but
> not nearly as bad as, say, thread-based concurrency with race
> conditions and deadlock. Manual memory management is much 
> simpler to
> deal with than many other things programmers already take on
> voluntarily.
> When you want your realtime application to behave in a certain 
> way,
> would you rather spend months or years working on the GC and 
> program
> in a completely difficult style to deal with the issue, or use 
> manual
> memory management *now* and deal with the slightly more 
> difficult
> programming model? Cost/benefit wise, GC just doesn't make a 
> lot of
> sense in this sort of scenario unless you have a lot of 
> resources to
> burn or a specific reason to choose a GC-mandatory platform.
> Again, I'm not saying GC is bad, I'm saying that in this area, 
> the
> cost/benefit ratio doesn't say you should spend your time 
> improving
> the GC to make things work. For everyone else, GC is great, and 
> I
> applaud David Simcha's efforts to improve D's GC performance.

It does take years but please note that those referenced papers 
are already several years old. Some are from 2005-6.
It doesn't mean D shouldn't support manual memory management but 
claiming that GC doesn't work for real-time is a [religious] 
myth. Clearly the cost of research has already been spent years 
ago and the algorithms were already documented and tested.

OT: one of the papers was written at my university.

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