Reference to instance variables inside a block

Question

Suppose I have a class (non-ARC environment):

@interface SomeObject : NSObject {
    UILabel *someLabel;
    dispatch_queue_t queue;
}
- (void)doAsyncStuff;
- (void)doAnimation;
@end

@implementation SomeObject

- (id)init {
    self = [super init];
    if (self) {
        someLabel = [[UILabel alloc] init];
        someLabel.text = @"Just inited";
        queue = dispatch_queue_create("com.me.myqueue", DISPATCH_QUEUE_SERIAL);
    }
    return self;
}

- (void)doAsyncStuff {
    dispatch_async(queue, ^{
        ...
        // Do some stuff on the current thread, might take a while
        ...
        dispatch_async(dispatch_get_main_queue(), ^{
            someLabel.text = [text stringByAppendingString:@" in block"];
            [self doAnimation];
        }
    }
}

- (void)doAnimation {
    ...
    // Does some animation in the UI
    ...
}

- (void)dealloc {
    if (queue) {
        dispatch_release(queue);
    }
    [someLabel release];
    [super dealloc];
}

If my block gets kicked off and then everything else holding a reference to the instance of this object releases it, am I guaranteed that dealloc won't be called because the nested block refers to an instance variable (and to self) -- that dealloc will happen after the nested block exits? My understanding is that my block has a strong reference to self, so this should be kosher.

Answer 1

This is fine, for the reasons you've stated.

The important thing to note is that you would create a retain cycle, if the class (represented by self) retained the block in any way. Because you're defining it in-line, and passing it to dispatch_async, you should be ok.