On 10/9/13 6:06 AM, Michel Fortin wrote:
On 2013-10-09 07:33:29 +0000, Manu <[email protected]> said:
Is there more to it? Cleaning up circular references I guess... what does
Apple do?
Apple implemented auto-nulling weak pointers for ARC (as well as
__unsafe_unretained ones if you are not afraid of dangling pointers).
Yah, the rub being the programmer must use weak pointers judiciously.
The difficulty is in "judiciously" :o).
It's an uncommon edge case, so there's gotta be heaps of room for
efficient
solutions to that (afaik) one edge case. Are there others?
I don't know about you, but circular references are not rare at all in
my code.
Nor Facebook's. I can't give away numbers, but the fraction of cycles
per total memory allocated averaged over all of Facebook's PHP programs
(PHP being reference counted) is staggering. Staggering!
If PHP didn't follow a stateless request model (which allows us to use
region allocation and reclaim all memory upon the request's end), we'd
be literally unable to run a server for more than a few minutes.
Another solution that could be used for circular references is to have
the stop-the-world GC we have now collect them. Reference counting could
be used to free GC memory in advance (in the absence of circular
references), so the GC would have less garbage to collect when it runs.
Yah, that seems to be a good approach for us.
Andrei
