Here is a trick to help you better understand how to use autorelease pools
correctly. Put this in a header somewhere:
static inline void subpool(void (^block)(void))
{
NSAutoreleasePool *_pool = [[NSAutoreleasePool alloc] init];
block();
[pool drain];
}
… and use it like so:
subpool(^{
// do stuff
});
And if you need to get stuff out of a subpool:
__block NSThingy *t = nil;
subpool(^{
t = [other getThingy];
[t retain]; // because getThingy might return autoreleased
});
[t doSomething];
[t release]; // balance the earlier retain
t = nil;
On May 14, 2011, at 6:19 PM, Nick Zitzmann wrote:
>
> On May 14, 2011, at 5:43 PM, Martin Batholdy wrote:
>
>> I still have trouble understanding the autorelease pool.
>>
>> Lets assume an object Z has a method where it gets a string y and returns
>> another string x.
>>
>> Now when an instance of this object is created and the method is invoked,
>> x is returned and is used somewhere else.
>>
>> Now this method of object Z should not be the owner of x right?
>> Because x is used elsewhere.
>>
>>
>> So I add x to the autorelease-pool to declare that I am not the owner (and
>> won't send it a release message);
>>
>> x = [[[NSString alloc] init] autorelease];
>>
>>
>> but where do I release the pool?
>> And to which pool is it added?
>
> Pay attention to the memory management rules:
> <http://developer.apple.com/library/mac/#documentation/Cocoa/Conceptual/MemoryMgmt/Articles/mmRules.html>
>
>> I thought I would create my own pool in the init-method of Z and send it a
>> [pool release] message in the alloc-method.
>>
>> But I haven't seen that so far in sample code ...
>
> Don't ever do that. You'll wind up popping objects that aren't supposed to be
> popped yet, which will lead to a crash. Autorelease pools should never be
> used as ivars, globals, or static variables.
>
> In general, you shouldn't create your own autorelease pools, unless (1) you
> are using NSThread or pthread to create new threads, or (2) you have written
> a loop that generates a great deal of temporary objects that need to be
> popped from time to time to keep memory usage from spiking, and you know what
> you're doing.
>
>> can someone explain me what happens when I add x to the autorelease pool?
>
> Read the autorelease pools article in the memory management programming guide
> (see link above) and it will clear things up.
>
> Nick Zitzmann
> <http://www.chronosnet.com/>
>
>
>
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