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.
