Smart pointers instead of GC?

[Adam Wilson]

On Fri, 31 Jan 2014 23:35:44 -0800, Manu <turkeyman at gmail.com> wrote:

> On 1 February 2014 16:26, Adam Wilson <flyboynw at gmail.com> wrote:
>
>> On Fri, 31 Jan 2014 21:29:04 -0800, Manu <turkeyman at gmail.com> wrote:
>>
>>  On 26 December 2012 00:48, Sven Over <dlang at svenover.de> wrote:
>>>
>>>   std.typecons.RefCounted!T
>>>>
>>>>>
>>>>> core.memory.GC.disable();
>>>>>
>>>>>
>>>> Wow. That was easy.
>>>>
>>>> I see, D's claim of being a multi-paradigm language is not false.
>>>>
>>>
>>>
>>> It's not a realistic suggestion. Everything you want to link uses the  
>>> GC,
>>> and the language its self also uses the GC. Unless you write software  
>>> in
>>> complete isolation and forego many valuable features, it's not a  
>>> solution.
>>>
>>>
>>>  Phobos does rely on the GC to some extent. Most algorithms and ranges  
>>> do
>>>
>>>> not though.
>>>>>
>>>>>
>>>> Running (library) code that was written with GC in mind and turning GC
>>>> off
>>>> doesn't sound ideal.
>>>>
>>>> But maybe this allows me to familiarise myself more with D. Who knows,
>>>> maybe I can learn to stop worrying and love garbage collection.
>>>>
>>>> Thanks for your help!
>>>>
>>>>
>>> I've been trying to learn to love the GC for as long as I've been  
>>> around
>>> here. I really wanted to break that mental barrier, but it hasn't
>>> happened.
>>> In fact, I am more than ever convinced that the GC won't do. My  
>>> current #1
>>> wishlist item for D is the ability to use a reference counted  
>>> collector in
>>> place of the built-in GC.
>>> You're not alone :)
>>>
>>> I write realtime and memory-constrained software (console games), and  
>>> for
>>> me, I think the biggest issue that can never be solved is the
>>> non-deterministic nature of the collect cycles, and the unknowable  
>>> memory
>>> footprint of the application. You can't make any guarantees or  
>>> predictions
>>> about the GC, which is fundamentally incompatible with realtime  
>>> software.
>>> Language-level ARC would probably do quite nicely for the miscellaneous
>>> allocations. Obviously, bulk allocations are still usually best  
>>> handled in
>>> a context sensitive manner; ie, regions/pools/freelists/whatever, but  
>>> the
>>> convenience of the GC paradigm does offer some interesting and  
>>> massively
>>> time-saving features to D.
>>> Everyone will always refer you to RefCounted, which mangles your types  
>>> and
>>> pollutes your code, but aside from that, for ARC to be useful, it  
>>> needs to
>>> be supported at the language-level, such that the language/optimiser is
>>> able to optimise out redundant incref/decref calls, and also that it is
>>> compatible with immutable (you can't manage a refcount if the object is
>>> immutable).
>>>
>>
>> The problem isn't GC's per se. But D's horribly naive implementation,
>> games are written on GC languages now all the time (Unity/.NET). And  
>> let's
>> be honest, games are kind of a speciality, games do things most programs
>> will never do.
>>
>> You might want to read the GC Handbook. GC's aren't bad, but most, like
>> the D GC, are just to simplistic for common usage today.
>
>
> Maybe a sufficiently advanced GC could address the performance
> non-determinism to an acceptable level, but you're still left with the
> memory non-determinism, and the conundrum that when your heap approaches
> full (which is _always_ on a games console), the GC has to work harder  
> and
> harder, and more often to try and keep the tiny little bit of overhead
> available.
> A GC heap by nature expects you to have lots of memory, and also lots of
> FREE memory.
>
> No serious console game I'm aware of has ever been written in a language
> with a GC. Casual games, or games that don't attempt to raise the bar may
> get away with it, but that's not the industry I work in.

That's kind of my point. You're asking for massive changes throughout the  
entire compiler to support what is becoming more of an edge case, not less  
of one. For the vast majority of use cases, a GC is the right call and D  
has to cater to the majority if it wants to gain any significant mindshare  
at all. You don't grow by increasing specialization...

-- 
Adam Wilson
GitHub/IRC: LightBender
Aurora Project Coordinator