Cocoa mail archive
Re: Use of Mac OS X 10.5 / Leopards Garbage Collection Considered Harmful
FROM : Alastair Houghton
DATE : Wed Feb 06 20:12:07 2008
On 6 Feb 2008, at 17:52, Hamish Allan wrote:
> On Feb 6, 2008 2:59 PM, John Engelhart <john.<email_removed>>
> wrote:
>
>> "I'll take 'Not relevant' for $200 and 'Misunderstands the
>> fundamentals' for the win, Alex."
>
> Speaking of "not relevant" and "misunderstands the fundamentals":
>
> 1) UTF8String returns a non-__strong pointer.
__strong isn't a type qualifier, it's an attribute (in the sense of
the __attribute__ keyword). The distinction is perhaps a bit subtle,
especially as attributes can be attached to a typedef'd type, but it's
the reason that you can put __strong anywhere in a variable
declaration and it still has the same effect. It *isn't* like const
or volatile, and the ANSI C rules regarding type qualifiers absolutely
*do not* apply.
Furthermore I *think* (and this is from memory, based on some work I
did on GCC several years ago, so I might be wrong) that if you write
something like
void * __strong MyFunction(void);
you'll find that the __strong attribute is attached to the *function*
rather than to the type. In any case it's going to be ignored because
__strong only really affects variables, not types or functions.
> 2) You fail to copy the data at that pointer.
> 3) You cry foul when that data disappears.
Well the bug is *either* ignoring the bit in the -UTF8String docs
where it says you should copy the string (though that does read like
it was only intended to talk about the non-GC case---I just filed <rdar://5727581
> asking for a clarification), or not using __strong on the variable
you're storing the result in.
>> A garbage collection systems sine qua non is to free the programmer
>> from having to deal with the issues memory allocation.
>
> Exactly. So stop getting your knickers in a twist about whether or not
> UTF8String actually returns memory from NSAllocateCollectable(), and
> simply copy the result as required by the documentation for
> UTF8String.
Indeed, I rather wish I hadn't mentioned NSAllocateCollectable(),
since I think it's only muddied the waters further.
Kind regards,
Alastair.
--
http://alastairs-place.net
DATE : Wed Feb 06 20:12:07 2008
On 6 Feb 2008, at 17:52, Hamish Allan wrote:
> On Feb 6, 2008 2:59 PM, John Engelhart <john.<email_removed>>
> wrote:
>
>> "I'll take 'Not relevant' for $200 and 'Misunderstands the
>> fundamentals' for the win, Alex."
>
> Speaking of "not relevant" and "misunderstands the fundamentals":
>
> 1) UTF8String returns a non-__strong pointer.
__strong isn't a type qualifier, it's an attribute (in the sense of
the __attribute__ keyword). The distinction is perhaps a bit subtle,
especially as attributes can be attached to a typedef'd type, but it's
the reason that you can put __strong anywhere in a variable
declaration and it still has the same effect. It *isn't* like const
or volatile, and the ANSI C rules regarding type qualifiers absolutely
*do not* apply.
Furthermore I *think* (and this is from memory, based on some work I
did on GCC several years ago, so I might be wrong) that if you write
something like
void * __strong MyFunction(void);
you'll find that the __strong attribute is attached to the *function*
rather than to the type. In any case it's going to be ignored because
__strong only really affects variables, not types or functions.
> 2) You fail to copy the data at that pointer.
> 3) You cry foul when that data disappears.
Well the bug is *either* ignoring the bit in the -UTF8String docs
where it says you should copy the string (though that does read like
it was only intended to talk about the non-GC case---I just filed <rdar://5727581
> asking for a clarification), or not using __strong on the variable
you're storing the result in.
>> A garbage collection systems sine qua non is to free the programmer
>> from having to deal with the issues memory allocation.
>
> Exactly. So stop getting your knickers in a twist about whether or not
> UTF8String actually returns memory from NSAllocateCollectable(), and
> simply copy the result as required by the documentation for
> UTF8String.
Indeed, I rather wish I hadn't mentioned NSAllocateCollectable(),
since I think it's only muddied the waters further.
Kind regards,
Alastair.
--
http://alastairs-place.net
