Re: GNUstep and valgrind

[Richard Frith-Macdonald]

> On 16 Mar 2018, at 16:53, Richard Frith-Macdonald 
> <richard.frith-macdonald@theengagehub.com> wrote:
> 
> 
> 
>> On 16 Mar 2018, at 15:44, Fred Kiefer <fredkiefer@gmx.de> wrote:
>> 
>> 
>> 
>>> Am 16.03.2018 um 16:32 schrieb Richard Frith-Macdonald 
>>> <richard.frith-macdonald@theengagehub.com>:
>>> 
>>> 
>>> 
>>>> On 16 Mar 2018, at 15:18, amon <amon@vnl.com> wrote:
>>>> 
>>>> 
>>>>         [arglist release];
>>>> arglist = [[[NSMutableString stringWithCString: [cmdline cString]]
>>>>            componentsSeparatedByString: DELIM] retain];
>>>> 
>>>> This happens inside an init. arglist is release by the dealloc
>>>> method. However, NSMutableString insists on making it autoreleased.
>>>> I want to make it not do that. 
>>> 
>>> Portable GNUstep code would look like this:
>>> 
>>> CREATE_AUTORELEASE_POOL(pool);
>>> ASSIGN(arglist, [[[NSMutableString stringWithCString: [cmdline cString]] 
>>> componentsSeparatedByString: DELIM]);
>>> DESTROY(pool);
>>> 
>>> with no wasted/leaked memory.
>> 
>> I have to disagree. This will get rid of the intermediate NSMutableString 
>> but later on when the surrounding Foo object gets released the arglist ivar 
>> will get released as well, but the component strings in that array will 
>> still remain in what ever autorelease pool is active at that time and will 
>> only get freed when that pool is cleaned up.
> 
> That's (almost always) wrong.  Releasing a container does not put its 
> contents into an autorelease pool, it releases them all. so the components 
> get released/deallocated at the point when the array is deallocated.
> 
> Of course you can never guarantee that a class will behave normally (if you 
> don't have access to its source code), but generally when an object is 
> deallocated it releases all its instance variables.
> 
> In this instance I think it's fair to assume we are talking about the GNUstep 
> NSMutableString class generating components in a GNUstep NSArray, so we know 
> that we don't have some perverse implementation and the above three-line 
> solution is all that's needed to ensure no leaked objects.
> 
> However, I agree that if someone had for instance re-implemented 
> -componentsSeparatedByString: in a category of NSMutableString, and their 
> re-implementation had created an NSArray subclass which, on deallocation, 
> would put the array contents into an autorelease pool rather than releasing 
> them, then you could get the situation you describe where the components 
> would be placed in a pool at the point when the array ivar is released.

Of course your example:

       // zone used = n bytes
       CREATE_AUTORELEASE_POOL(pool);
       obj = [Foo new];
       // zone used = n+m bytes
       [obj release];
       DESTROY(pool);
       // zone used = n bytes.

is perfect if what you care about the end result after finishing with the 
instance of Foo.

The other:

CREATE_AUTORELEASE_POOL(pool);
ASSIGN(arglist, [[[NSMutableString stringWithCString: [cmdline cString]] 
componentsSeparatedByString: DELIM]);
DESTROY(pool);

is what you'd do in a setter method of Foo, where the instance of Foo is 
long-lived and you want to ensure that you don't increase memory usage duriung 
that long life.