[Issue 3463] Integrate Precise Heap Scanning Into the GC

d-bugmail at puremagic.com d-bugmail at puremagic.com
Thu Apr 14 19:10:06 PDT 2011


http://d.puremagic.com/issues/show_bug.cgi?id=3463



--- Comment #117 from Vladimir <thecybershadow at gmail.com> 2011-04-14 19:06:29 PDT ---
(In reply to comment #116)
> Yes, they do. It's called the frame rate. (Though I'd guess to be technical, 
> this a soft-realtime requirement.)

That's exactly what I meant. Hard realtime means that missing a deadline is
equivalent to a complete system failure. Heap allocation is indeed not an
option in that case.

> Why do you think the GC will get slower? One of the major points of a precise
> GC is that it does less total work than a conservative GC. Why? Because
> following a pointer, even if it goes nowhere, is an expensive operation (I'd
> guess O(log Heap_Size)) to say nothing of the cost of keeping around and
> tracing the excess garbage. And the more precision the GC has, the less
> pointers it has to trace per unit memory and the total memory traced is reduced
> as well. So it's win-win.

I hope it is as you say it is, but without benchmarks it's hard to say
anything, and this talk of state machines etc. is disconcerting. Note that the
current GC does a quick check for each possible pointer if it's between the low
and high address range of all GC pages - for small heaps, this weeds out most
false pointers.

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