Memory management and performSelectorInBackground:

Question

Which is right? This:

NSArray* foo = [[NSArray alloc] initWithObjects:@\"a\", @\"b\", nil];
[bar performSelectorInBackground:@selector(baz:) withObject:foo];         


        

Answer 1

First is wrong.

performSelectorInBackground:withObject: retains both bar and foo until task is performed. Thus, you should autorelease foo when you create it and let performSelectorInBackground:withObject take care of the rest. See documentation

Latter is correct because you autorelease foo when you create it. Autorelease pool that you create inside baz has nothing do with correctness of foo's memory management. That autorelease pool is needed for autoreleased objects inside pool allocation and release in baz, it doesn't touch foo's retain count at all.

Answer 2

The correct approach now would in fact be to do:

NSArray* foo = [[[NSArray alloc] initWithObjects:@"a", @"b", nil] autorelease];
[bar performSelectorInBackground:@selector(baz:) withObject:foo];

- (void)baz:(NSArray*)foo {
    @autoreleasepool {
        ...
    }
}