Question

This code down below works as expected, cleans things up without Zombies. The class in which this method exists, is the owner of the Nodes, which are being released, yet, upon “Analyze” the following 2 issues show up.

If possible, could you help me understand why?

- (void) dealloc {  
    NSLog(@"Releasing [Doubly Linked List] .. ");

    Node *thisNode = [self firstNode]; 
    Node *nextNode = [thisNode next];

    while (nextNode != nil) {

        // If "Next node" is not nil, it means that
        //   "previous node" can now be released

        NSLog(@"    - releasing node \"%c\"", [[nextNode previous] charData]);
        [[nextNode previous] release];

        nextNode = [nextNode next];
    }

    [[self lastNode] release];
    [super dealloc];
}

Answer 1

Click on the icon on the left of the message, it will show the path through the code that produces the error.

You are releasing something, [nextNode previous] that you do not own. In particular you did not alloc or retain it nor obtain it from a method that begins with new or copy so you do not have ownership of it and should not release it.

It is also very uncommon to release something not in your class, [[nextNode previous] release].

Now: [[self lastNode] release];

As above you did not obtain an ownership on the object you are releasing.

If lastNode is a property with retain you are subverting the setter and when later a value is assigned to lastNode via the setter there will be an extra release on the object and probably a crash. If it is not a property again this it very non-standard to release something that is returned by a method call.

Any releases with code of this form [[self lastNode] release] is non-standard and if be avoided there will be fewer ownership (retain/release) problems.

You will save a lot of time and grief by studying the Apple memory management documentation.