On 23/11/2012, Basile Starynkevitch <bas...@starynkevitch.net> wrote: > On Thu, Nov 22, 2012 at 09:29:43PM +0100, Florian Weimer wrote: >> On 11/18/2012 07:06 PM, NightStrike wrote: >> >> >What's wrong with std::shared_ptr? >> >> The pointer needs two words, and the per-object overhead for the >> reference counts etc. is four words, if I'm counting correctly. >> >> (Other forms of reference counting have less overhead, of course, >> but you were asking about std::shared_ptr.) > > > Actually, this observation may favor a real garbage collector. Marking GC as > simple as ggc+gengtype usually have one (or a few) mark bits, so can consume > only a few bits (or perhaps a byte in some mark array) per object. Copying > GC could avoid consuming any more storage per object. Of course useless > object may stay in memory for a while -until the GC deletes them or reuse > their memory-
The research shows significantly higher memory usage when relying on GC in large systems. > but that observation is also true with traditional C++ "GC" > techniques like shared_ptr .... An object may be freed later than what > should be possible. Only if the code has a bug. Destructors are predictable, immediate and deterministic. > And some GC techniques are quite friendly with L1 or L2 caches on the > processor chip. And so are some reference counting techniques with intrusive counts, or using std::make_shared(), so the object and refcount are adjacent in memory.
