On 31.07.2013, at 22:01, Greg Parker <gpar...@apple.com> wrote:
> On Jul 31, 2013, at 12:28 PM, Vincent Habchi <vi...@macports.org> wrote:
>> David Duncan wrote:
>>> Why would there be? Your just asking for a mutable copy of an empty string.
>>> It should be equivalent to [[NSMutableString alloc] initWithString:@« »]
>>
>> But much slower I expect, since it creates a NSString, takes a mutable copy,
>> then implicitly releases the constant empty NSString.
>
> For giggles I tried some NSMutableString allocation patterns into my
> microbenchmark test harness.
>
> Simple alloc/init is the fastest:
>
> 100 [[[NSMutableString alloc] init] release]
> 102 [[NSMutableString new] release]
> 109 [NSMutableString string] // ARC enabled
> 117 [[@"" mutableCopy] release]
> 119 @autoreleasepool { [NSMutableString string]; } // ARC disabled
> 129 [[[NSMutableString alloc] initWithString:@""] release]
>
> (Smaller numbers are better. Numbers are getrusage(RUSAGE_SELF) time for
> 10000000 iterations, normalized to fastest=100. Your mileage may vary.)
How much time contributes the allocation of the raw storage? I would guess that
initializing an empty string is quite fast (while generally NSString is
disappointing slow in almost all other functions).
What's also interesting is the time it takes to *deallocate* an object. Since
ARC and weak pointers, this time increased dramatically (due to the requirement
to remove the object from the "sparse array").
In those micro-benchmarks its also interesting how this benchmark affects the
behavior of the heap. It's likely we see a particular edge case which is either
fast or slow. I would expect that allocating and deallocating the same object
in a loop leads to faster allocation times. As opposed to the case where
differrent objects are allocated and deallocated in random order.
Andreas
>
> ARC and non-ARC scores are the same within measurement noise, except for
> [NSMutableString string] where ARC can optimize the autoreleased return value
> so the test doesn't need to spin the autorelease pool. Note th
>
>
>> BTW, what’s the difference between [[NSMutableString alloc] init] and
>> [[NSMutableString alloc] initWithString:@“”]?
>
> Semantically there's no difference: you get the same string with the same
> retain count.
>
>
> --
> Greg Parker gpar...@apple.com Runtime Wrangler
_______________________________________________
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
