Open Radar

 
Summary:

NSData objects decoded from an NSKeyedUnarchiver are returned with a net retain count of 1. They should be returned with a net retain count of +0 (i.e. autoreleased exactly as many times as they are retained). On the simulator the behaviour is correct, on the device it fails.

Steps to Reproduce:

-(void)someFunction
{
    @autoreleasepool
    {
        NSData *fileData = [NSData dataWithContentsOfFile:storagePath options:NSDataReadingUncached error:&error];
        MyThing *obj = [[NSKeyedUnarchiver unarchiveObjectWithData:fileData] retain];
    }
    [MyThing release];
}
…
@implementation MyThing
-(id)initWithCoder:(NSCoder *)aDecoder
{
    self = [super init];
    if (self)
    {
        myData = [[aDecoder decodeObjectForKey:kDataKey] retain];
    }
    return self;
}

-(void)dealloc
{
    [myData release];
    [super dealloc];
}
@end

Call -someFunction and watch the heap growth/leaks instrument.

Expected Results:
Net heap growth is zero. Nothing is leaked.

Actual Results:
Net heap growth is the size of the decoded data object. The NSData object decoded from the archive is leaked.

Regression:
Unknown. Needs fixing anyway.

Notes:
There is no suitable workaround - if I insert an extra call to explicitly release it my app will explode if you fix this, or if it is run on a version of iOS before the problem was introduced.