On Apr 24, 2009, at 11:55 PM, Andreas Grosam wrote:
I get strange memory leaks when I use KVO. The setup of all classes
is OK as far as I can see, and the KVO is actually working. There is
no memory leak when the classes will be tested in test cases without
KVO.
There are two classes involved:
class Model and class Observer
Model has a property port where observer listens for change events.
The leak only occurs when KVO actually sends a change event.
Otherwise, there are no leaks, even when KVO is established but no
message has been sent. So it is quite probable that the source of
the leak is within KVO code. The object leaking is obviously the
receiver for the addObserver message, namely the model.
The leak is always only for one object and plus all the objects that
are retained by model, no matter how often instances of Model will
be created and KVO established.
For instance, doing this in a loop: creating observer and model,
establish KVO, then causing a KVO event, tearing down everything --
will only produce one leak from object model (plus the leaks from
retained objects).
Correction:
This statement is actually not correct. The number of leaks is
"almost" proportional to the number of loops. However, some "leaks"
seem to be reused or will not be detected.
This of course makes the thing much more worse.
Here is the code for the observer that adds itself as an observer
who listens at property "port" of model.
@implementation Observer
- (void) registerObserver
{
[model addObserver:self forKeyPath:@"port"
options:NSKeyValueObservingOptionNew context:NULL];
}
Here is the notification method for observer:
-(void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object
change:(NSDictionary *)change context:(void
*)context
{
NSDate *date = [NSDate date];
NSString *formattedDateString = [dateFormatter
stringFromDate:date];
NSLog(@"%@: %@", formattedDateString, keyPath);
}
The model spawns a thread who's run method installs a NSTimer in
the RunLoop. The timer handler then finally changes the value of
property port of model. When the work is done, it is ensured, that
the thread exits properly and releases all retained objects. After
the thread function has been exited, the observer model and the
observer will be released.
Note: The notification method observeValueForKeyPath will be invoked
in a different thread than the main thread, where the KVO has been
established.
The application runs currently in a Unit Test as a test case from
the google toolbox for mac, on the iPhone. When the test case
finishes, all objects should be deallocated.
So, what do I see here? Any thoughts what could cause the leaks?
Thanks for help
Regards
Andreas
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