Re: Speed Traps
Re: Speed Traps
- Subject: Re: Speed Traps
- From: Nat! <email@hidden>
- Date: Mon, 19 May 2003 23:22:20 +0200
Am Montag, 19.05.03 um 12:13 Uhr schrieb Marcel Weiher:
On Monday, May 19, 2003, at 02:20 Uhr, Kevin Elliott wrote:
With all due respect, how is "the performance is nearly the same"
very different than "the difference isn't all that noticeable"?
It is "very different" in that the difference is ONLY not all that
noticeable if you use NSObject's brain-dead refcount implementation,
which is in itself several times slower than an inline reference count
(almost 10 times for an optimized inline refcount). The reason it is
so slow is that every refcount operation requires a hash lookup and
possibly allocation/deallocation of the slot for the extra-refcount
inserted into the table. Nobody in their right mind uses that,
certainly Apple doesn't. All Apple-provided classes use some sort of
inline refcount.
I remember I actually once reverted back from inline ref counting to
the Apple way, when I wrote the MulleSybaseEOAdaptor. When I
implemented inline ref-counting on certain classes, things went slower,
when I was fetching a lot (really a lot!) of objects. Then I figured it
like this (It's been a while, but I think I stil got it about right)
If your objects stay at a retain count of 1, then the Apple code does
not need to create an entry in the hash table (1 being the default for
an object), this saves 32 bit. The decrease in speed I saw, was
probably due to the fact that (quite a few) more memory pages had to be
allocated from the OS, for the inline reference count overhead (my
objects were small).
The merit of the default implementation is still dubious IMO,
nevertheless it would be interesting to figure out how many objects
typically in their lifetime exceed a retain count of 1.
Ciao
Nat!
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and it's ending one minute at a time. -- Palahniuk
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