> On Aug 10, 2017, at 11:13 AM, Charles Srstka <cocoa...@charlessoft.com> wrote: >> On Aug 10, 2017, at 9:44 AM, Alastair Houghton >> <alast...@alastairs-place.net> wrote: >> >> On 10 Aug 2017, at 15:24, Jeremy Hughes <moon.rab...@virginmedia.com >> <mailto:moon.rab...@virginmedia.com>> wrote: >>> >>>> On 10 Aug 2017, at 15:15, Alastair Houghton <alast...@alastairs-place.net >>>> <mailto:alast...@alastairs-place.net>> wrote: >>>> >>>> On 10 Aug 2017, at 15:09, Charles Srstka <cocoa...@charlessoft.com >>>> <mailto:cocoa...@charlessoft.com>> wrote: >>>>> >>>>> They’re equivalent syntactically, but performance-wise, +array and >>>>> friends will cause the object to be put into an autorelease pool. >>>>> Therefore, +new is better for performance. >>>> >>>> Not with ARC they don’t. The ARC logic circumvents the autorelease pool >>>> in that case. >>> >>> Are you sure? >> >> Yes, I’m sure. At the call site, ARC causes the compiler to emit a call to >> objc_retainAutoreleasedReturnValue() or >> objc_unsafeClaimAutoreleasedReturnValue(), while in the method itself, ARC >> will use objc_autoreleaseReturnValue() or >> objc_retainAutoreleaseReturnValue(). The latter looks at the code for the >> call site and, assuming it matches, it will *not* do the autorelease and >> will set a flag that causes objc_retainAutoreleasedReturnValue() to >> eliminate the retain. > > The frameworks (and thus, the implementation of +array) are not built using > ARC. The -autorelease method is called manually, and the object is put in the > autorelease pool. You can see this for yourself by making a small test app > that calls [NSMutableArray array] and running it in Instruments, where the > autorelease will be clearly visible.
Autoreleases done by -autorelease can still be reclaimed by objc_retainAutoreleasedReturnValue. The autorelease-reclaim optimization is not reliable, and there are a number of caveats that make testing it tricky. That is why we generally refer to it as an optimization, rather than claiming it as a semantic guarantee. In your test app, you are almost certainly running into a well-known problem where the first attempt to reclaim an autorelease fails on x86-64 (because of a detail of dynamic linking). John. _______________________________________________ Cocoa-dev mailing list (Cocoa-dev@lists.apple.com) Please do not post admin requests or moderator comments to the list. Contact the moderators at cocoa-dev-admins(at)lists.apple.com Help/Unsubscribe/Update your Subscription: https://lists.apple.com/mailman/options/cocoa-dev/archive%40mail-archive.com This email sent to arch...@mail-archive.com
