NSData release is not reclaiming memory

Question

iPhoneOS 3.2

I use NSKeyedUnarchiver's unarchiveObjectWithFile: to load a custom object that contains a single large NSData and another much smaller object. The dealloc method in my custom object gets called, the NSData object is released, its retainCount == 1 just before. Physical memory does not decrement by any amount, let alone a fraction of the NSData size, and with repetition memory warnings are reliably generated: I have test until I actually received level 2 warnings. =(

NSString *archivePath = [[[NSBundle mainBundle] pathForResource:@"lingering"]
     ofType:@"data"] retain];
lingeringDataContainer = [[NSKeyedUnarchiver unarchiveObjectWithFile:archivePath] retain];
[archivePath release];
[lingeringDataContainer release];

and now the dealloc....

- (void) dealloc {
   [releasingObject release];
   [lingeringData release]; 
   [super dealloc];
}

Before release:

(gdb) p (int) [(NSData *) lingeringData retainCount]
$1 = 1

After:

(gdb) p (int) [(NSData *) lingeringData retainCount]
Target does not respond to this message selector.

Answer 1

First, you're retaining and releasing objects which do not need to have that happen to them. Here's the cleaned up code:

NSString *archivePath = [[NSBundle mainBundle] pathForResource:@"lingering"]
     ofType:@"data"]; // Do not retain again.
lingeringDataContainer = [NSKeyedUnarchiver unarchiveObjectWithFile:archivePath]; // Do not retain again.
// Do not release, because archivePath is already autoreleaed: [archivePath release];
// Again, this is already autoreleased: [lingeringDataContainer release];

Or more simply:

NSString *archivePath = [[NSBundle mainBundle] pathForResource:@"lingering"]
     ofType:@"data"];
lingeringDataContainer = [NSKeyedUnarchiver unarchiveObjectWithFile:archivePath]; 

Second, where's the rest of the code? It's probably something else which is being retained or cached somewhere else.

Answer 2

When are you checking the memory usage? Is it just after the code snippet you posted? archivePath and lingeringDataContainer are both autoreleased. They will not be deallocated until (at least) the autorelease pool is drained (usually at the end of the current event). There may also be a lot of other internal stuff that has been autoreleased and won't go away until the pool is drained.

Try doing this:

NSAutoreleasePool* pool = [[NSAutoreleasePool alloc] init]; // <==
NSString *archivePath = [[[NSBundle mainBundle] pathForResource:@"lingering"]
 ofType:@"data"] retain];
lingeringDataContainer = [[NSKeyedUnarchiver unarchiveObjectWithFile:archivePath] retain];
[pool release];                                             // <==
[archivePath release];
[lingeringDataContainer release];