Question

References to local variables (including ivars) inside blocks are automatically retained to make sure it remains valid throughout the execution of the block.

That said, would this code lead to a premature deallocation of self.message, since the first block does not reference it, even though the second block does? Or is it smart enough to know it should be retained?

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
    /* snip */
    dispatch_async(dispatch_get_main_queue(), ^{
        if ([self.message.ID isEqualToString:@"foobar"]) {
            /* snip */
        }
    });
});

Answer 1

A block captures all variables inside it, including nested blocks. In short: it does the “right” thing.

In this particular case, note that it’s self that’s being captured, not self.message.