Disadvantages of ARC

[Andrei Alexandrescu]

On 2/6/14, 7:11 AM, ponce wrote:
> On Thursday, 6 February 2014 at 11:37:59 UTC, Max Klyga wrote:
>> Anti-GC crowd tries to promote ARC as an deterministic alternative for
>> memory management.
>> I noticed that people promoting ARC do not provide any disadvantages
>> for proposed approach.
>>
>> The thing is in gamedev and other soft-realitime software background
>> only a handfull types of resources are really managed by RC and memory
>> usage patterns are VERY specific to their domain (mostly linear
>> allocation/deallocation and objects with non deterministic lifetime
>> are preallocated in pools).
>>
>> Trying to use RC as a general method of memory management leads to
>> some problems.
>> A pretty detailed view by John Harrop (He is somewhat known for
>> trolling in PL community, but nonetheless knows what he is talking
>> about) -
>> http://www.quora.com/Computer-Programming/How-do-reference-counting-and-garbage-collection-compare/answer/Jon-Harrop-1?srid=3Gvg&share=1#
>>
>>
>>
>> So RC could also introduce unpredictable pause times at undesired places.
>>
>> This is also confirmed by research from HP -
>> http://www.hpl.hp.com/personal/Hans_Boehm/popl04/refcnt.pdf
>>
>> My point is that we should not ruin the language ease of use. We do
>> need to deal with Phobos internal allocations, but we should not
>> switch to ARC as a default memory management scheme. In practice
>> people promoting ARC will probably not use phobos anyway. Currently
>> its just an excuse to not use D.
>>
>> Look at c++ and STL, etc. People will roll their own solutions no
>> matter what you try.
>
> I think of RC as a greater evil that GC. From what I've seen it does
> creates leaking cycles in tree structures AND pauses. From a low-level
> point of view, RC pointers are ugly (separate counter that will trash
> your cache) and do atomics all over the place (ie. memory barriers).
> That they don't have to because of shared is TBD.
>
> It is comforting to me to know that a GC pointer is still just a
> pointer. If we go the RC route, we will have to constantly think about
> the higher cost of RC pointer vs weak-ref, instead of thinking about
> other things instead
> Right now a GC pointer is the same size as a non-GC one, it's liberating.
>
> It looks like we want to solve a PR problem more than a real one.

Though I partly agree with your considerations, let me note that PR 
problems are real.

Andrei