Am 15.07.2014 22:58, schrieb deadalnix:
On Tuesday, 15 July 2014 at 20:03:15 UTC, Chris wrote:
From the link above:
"It’s a common but false belief that reference counting (using shared
pointers in particular) is better than garbage collection. There is
actual research* showing that the two approaches are just two sides of
the same coin. You should realize that deleting a shared pointer may
lead to an arbitrary long pause in program execution, with similar
performance characteristics as a garbage sweep. It’s not only because
every serious reference counting algorithm must be able to deal with
cycles, but also because every time a reference count goes to zero on
a piece of data a whole graph of pointers reachable from that object
has to be traversed. A data structure built with shared pointers might
take a long time to delete and, except for simple cases, you’ll never
know which shared pointer will go out of scope last and trigger it."
* http://www.cs.virginia.edu/~cs415/reading/bacon-garbage.pdf
Yes but D's GC is crap. I actually wanted to a a quick hack in it
recently to avoid going through the lock every time for every
operation, but ended up giving up. Also the API between the GC
and the compiler need to be reworked.
Which boils down to having to improve the GC implementation, not that GC
in general is bad.
Finally someone posted here a research paper from ibm if memory
serve. It show that ref counting is a win for single threaded
code, but is a net loose when sharing across thread, because of
the synchronization overhead (especially the hammering of the
cache line containing the reference count).
Which given the fact that most computers nowadays, even embedded ones,
are becoming at very least dual core, is quite important fact.
--
Paulo
