[Issue 3463] Integrate Precise Heap Scanning Into the GC

[d-bugmail at puremagic.com]

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



--- Comment #125 from Walter Bright <bugzilla at digitalmars.com> 2011-04-14 20:33:11 PDT ---
(In reply to comment #120)
> I understand the advantages of a moving GC - heap compaction allowing for an
> overall smaller managed heap etc., but I hope you understand that sacrificing
> speed for these goals is not an unilateral improvement for everyone.

In a gc, speed really is the paramount consideration. (The problem with
excessive memory consumption is speed, after all.)

Unfortunately, the speed of any gc strategy cannot be determined in advance.
One has to try it, profile it, and tune it to see if it is an overall
improvement.

The theoretical speed improvement of more precise gc comes from:

1. the collector doing less work because it knows where the actual pointers are
rather than having to scan for them

2. not following and scanning memory that is falsely pointed to by an integer

3. reducing the working set of memory, meaning less work for scanning

The theoretical speed decrease comes from:

1. more work to read the pointer tables

2. possibly a large hit from using a virtual function

How this will play out will require actually trying it.

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