limit on using autorelease pools in ios

Question

How many autorelease you can create in your application? Is there any limit?

I searched for an answer in google, but didn't get any useful info.

And

int main(){

NSAutoreleasepool *pool = [NSAutoreleasepool alloc]init];

NSString *str = [NSString alloc]init];

[pool drain];
}

In google, i found this sample in almost all the articles. With the above code, if we do analyze in Xcode it throws memory leak. Instead if we alloc str in this way NSString *str = [NSString alloc]init]autorelease;

then it does not throw any memory leak.

Which way is correct.

Also in the above code, i found that when [pool drain] statement is executed, then the variable str is released. When we write the same code using "@autorelease" keyword instead of NSAutoreleasePool, what happens. I mean there won't be any statement like [pool drain] if we use @autorelease.

I mean in this way

int main(){

@autorelease{
NSString *str = [NSString alloc]init];
}
}

Thanks Jithen

Answer 1

The use of an NSAutoreleasePool or @autorelease is not for fixing memory leaks. Their use is to help control the scope of when autoreleased objects are released. You need to do proper memory management regardless of whether you use any autorelease pools or not.

In the first block of code you posted, you get a memory leaks because you allocate a string but you never call release on the object. In this case, str is not an autoreleased object. The autorelease pool has no effect on this object.

When you added the call to autorelease on the string, then the object gets queued to be autoreleased at some point. Draining the autorelease pool triggers that release.

Your last code using @autorlease is identical to the first block of code. You don't properly release str so it will leak. But again, this has nothing to do with the autorelease pool.

Enabling ARC would fix your issue for the first and last blocks of code you posted. ARC would take care of releasing str for you.

Edit: And as stated in the comment above, you can have as many autorelease pools as you need to control when autoreleased objects are actually released.