KVO is bloating my app

Question

Hi All
I've hit a snag with an app I'm building which I appreciate will be down to my lack of knowledge.
I have a class that monitors the input from a USB device. I've set up this class to be KVO compliant.
One of the instance variables of the driver class is given a constantly changing input 'Analog1'.
If I run the driver class and just NSLog out the value of 'Analog1' then I have no issues app runs with a constant Live Bytes of 2.24Mb with a stream of logs to the console.
So I'm pritty sure the driver class is fine. My issue is when I try to use KVO to observe the value of 'Analog1' so I can react to it or have it display the value on screen.
I have a AppController class which I intend to use for the main nib. In the init method of the AppController I have the following:
- (id)init
    self = [super init];
    if (self) {
             k8055CardAddress0 = [[CCVellemanK8055Driver alloc] initWithCardAddress : 0 ];
             // Setup KVO
             [k8055CardAddress0 addObserver:self forKeyPath:@"k8055AnalogInput1" options:NSKeyValueObservingOptionNew context:NULL];
    return self;
I then have the observe method which I would use to react to the key value of k8055AnalogInput1.
- (void) observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context
    NSLog(@"Value is changing");
Now I have prviously had a number of actions in here but due to ripping it a part to find the cause of the bloat we'll leave the example as above.
As you can imaging it now logs every time a value is changed. (Which is a lot an quickly - lets say 10 times a second).
Right so here's the issue when I run instruments and have leaks and allocations on there are no leeks but there's a tiny allocation been made and in the Statistics > Object Summary there's a CFNumber which constantly grows.. and grows... and well you get the picture. Run it long enough and a 2.24Mb app gets very large in no time at all.
There's clearly something KVO is doing that I should be releasing but I don't know what.
Any assistance would be most appreciated.
Cheers
Steve

Answer 1

I don't know if the following will help someone point me in the right direction but the offending CFNumber which is growing in instruments gives the following on
Allocations > Statistics > Object Summary > CFNumber
Address
Category
Timestamp
Live
Size
Responsible Library
Responsible Caller
6275
0x100175f70
CFNumber
00:37.343.141
32
Foundation
-[NSPlaceholderNumber initWithInt:]
6276
0x1001788d0
CFNumber
00:37.343.182
32
Foundation
-[NSPlaceholderNumber initWithDouble:]
6277
0x100162f30
CFNumber
00:37.343.225
32
Foundation
-[NSPlaceholderNumber initWithDouble:]
These 3 Objects? are constantly repeated hence the growing memory prob.
If you click on each of these they produce the following:
Address
Category
Event Type
RefCt
Timestamp
Size
Responsible Library
Responsible Caller
0
0x100175f70
CFNumber
Malloc
1
00:37.343.141
32
Foundation
-[NSPlaceholderNumber initWithInt:]
1
0x100175f70
CFNumber
Autorelease
<null>
00:37.343.143
0
Foundation
-[NSObject(NSKeyValueCoding) valueForKey:]
Address
Category
Event Type
RefCt
Timestamp
Size
Responsible Library
Responsible Caller
0
0x1001788d0
CFNumber
Malloc
1
00:37.343.182
32
Foundation
-[NSPlaceholderNumber initWithDouble:]
1
0x1001788d0
CFNumber
Autorelease
<null>
00:37.343.183
0
Foundation
-[NSObject(NSKeyValueCoding) valueForKey:]
2
0x1001788d0
CFNumber
CFRetain
2
00:37.343.185
0
AppKit
-[NSValueBinder _cacheObjectValue:]
3
0x1001788d0
CFNumber
CFRetain
3
00:37.343.188
0
AppKit
-[NSValueBinder _cacheDisplayValue:]
Address
Category
Event Type
RefCt
Timestamp
Size
Responsible Library
Responsible Caller
0
0x100162f30
CFNumber
Malloc
1
00:37.343.225
32
Foundation
-[NSPlaceholderNumber initWithDouble:]
1
0x100162f30
CFNumber
Autorelease
<null>
00:37.343.227
0
Foundation
-[NSObject(NSKeyValueCoding) valueForKey:]
2
0x100162f30
CFNumber
CFRetain
2
00:37.343.228
0
AppKit
-[NSValueBinder _cacheObjectValue:]
3
0x100162f30
CFNumber
CFRetain
3
00:37.343.231
0
AppKit
-[NSValueBinder _cacheDisplayValue:]
4
0x100162f30
CFNumber
CFRetain
4
00:37.343.235
0
AppKit
-[NSCell _setContents:]
5
0x100162f30
CFNumber
CFRetain
5
00:37.355.428
0
AppKit
-[NSCell _contents]
6
0x100162f30
CFNumber
Autorelease
<null>
00:37.355.430
0
AppKit
-[NSCell _hasAttributedStringValue]
7
0x100162f30
CFNumber
CFRetain
6
00:37.355.430
0
AppKit
-[NSCell _hasAttributedStringValue]
8
0x100162f30
CFNumber
CFRelease
5
00:37.355.431
0
AppKit
-[NSCell _hasAttributedStringValue]
9
0x100162f30
CFNumber
CFRetain
6
00:37.355.432
0
AppKit
-[NSCell _contents]
10
0x100162f30
CFNumber
Autorelease
<null>
00:37.355.433
0
AppKit
-[NSTextFieldCell drawInteriorWithFrame:inView:]
11
0x100162f30
CFNumber
CFRetain
7
00:37.355.433
0
AppKit
-[NSTextFieldCell drawInteriorWithFrame:inView:]
12
0x100162f30
CFNumber
CFRelease
6
00:37.355.474
0
AppKit
-[NSTextFieldCell drawInteriorWithFrame:inView:]
13
0x100162f30
CFNumber
CFRelease
5
00:37.357.203
0
AppKit
-[NSApplication nextEventMatchingMask:untilDate:inMode:dequeue:]
14
0x100162f30
CFNumber
CFRelease
4
00:37.357.203
0
AppKit
-[NSApplication nextEventMatchingMask:untilDate:inMode:dequeue:]
15
0x100162f30
CFNumber
CFRelease
3
12:40.043.237
0
AppKit
-[NSValueBinder _cacheObjectValue:]
16
0x100162f30
CFNumber
CFRelease
2
12:40.043.246
0
AppKit
-[NSValueBinder _cacheDisplayValue:]
17
0x100162f30
CFNumber
Autorelease
<null>
12:40.043.257
0
AppKit
-[NSCell setObjectValue:]
Cheers
Steve