On Friday, May 30, 2003, at 12:38 America/Denver, Chuck Messenger wrote:
Gregory Colvin wrote:Thanks, but your description of cyclic_ptr is pretty far off the mark.
Sorry -- hopefully you'll forgive my ignorance. I'm just throwing out what I understand to be the case, in the hopes that someone (such as yourself) would set me straight...
It does not maintain a global map, and copying cyclic_ptr cost the same
as copying shared_ptr.
OK, I'll have to review the old messages again. I thought someone had said cyclic_ptr used a global map. Sorry. I suppose better yet would be for me to study your actual *code*...
Larry's analysis gives a better explanation than I could.
Do you do a raw scan of memory, like sp_collector, then? (i.e. not perfect discovery)
No. The self-assignment trick is precise, unless it is foiled by a user-written operator=.
The special assignment mode is used only during the mark phase of a collection, and costs more or less the same as any other discovery method.
Suppose I have the structure:
struct Image { char huge_image[ONE_ZILLION]; cyclic_ptr<whatever> ptr; };
As I understand it, in order to discover 'ptr', you'd invoke operator=() on each Image structure you came to. Correct, or incorrect?
Correct. So it would be smart to write an operator= for Image that avoids copying huge_image to itself. And it would best if the uber-pointer used a less intrusive discovery method. I think sp_collector is on the right track, if it could be made precise.
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