Mac Apps That Use Garbage Collection Must Move to ARC

[H. S. Teoh via Digitalmars-d]

On Wed, Feb 25, 2015 at 04:36:22PM -0800, Walter Bright via Digitalmars-d wrote:
> On 2/25/2015 1:50 PM, deadalnix wrote:
> >On Wednesday, 25 February 2015 at 21:44:05 UTC, Andrei Alexandrescu wrote:
> >>>You seeing this completely one sided. Even if write barries make
> >>>code slower by 10% its a non issue if the GC collections get faster
> >>>by 10% as well. Then in average the program will run at the same
> >>>speed.
> >>
> >>Hmmmm... not sure the math works out that way. -- Andrei
> >
> >Yeah the math are wrong, but the general idea remains.
> >
> >I don't think it make sens to completely discard the idea of
> >barriers, especially when it come to write barrier on the immutable
> >heap. At least that should certainly pay off.
> 
> Part of the equation is D simply does not use GC anywhere near as
> pervasively as Java does, so the benefit/cost is greatly reduced for
> D.

Do you have data to back that up?

I don't know how typical this is, but in my own D code I tend to use
arrays a lot, and they do tend to add significant GC load. A recent
performance improvement attempt in one of my projects found that
collection cycles take up to 40% of total running time (it's a CPU-bound
process). Turning off GC collections and manually triggering them at
strategic points with lower frequency gave me huge performance
improvements, even though the collection cycles are still pretty slow.

I'm not sure how write barriers would play into this scenario, though.
The overall performance outside of GC collections would probably suffer
a bit, but it might be more than made up for by more accurate collection
cycles that take only a fraction of the time -- most of the scanned data
is live, only a small subset needs to be collected. A generational GC
would also greatly improve this particular use case, but that seems
really remote in D right now. In any case, a bit more investigation into
the actual costs/benefits of write barriers might give us more concrete
data to base decisions on, instead of just a blanket dismissal of the
whole idea.


T

-- 
It always amuses me that Windows has a Safe Mode during bootup. Does that mean that Windows is normally unsafe?