Memory leak in DDXML parser

Question

I load data from Internet, and parse it using DDXML parser in another thread. Here is code (callback connectionDidFinishLoading: is coming in background thread, I scheduled URLConnection at background thread):

- (void)connectionDidFinishLoading:(NSURLConnection *)connection
{
    NSLog(@"connection did finish load");
    NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
    DDXMLDocument *xdoc = [[DDXMLDocument alloc] initWithData: receivedXmlData options:0 error: NULL];
    NSLog(@"document retainCount1 = %d", [xdoc retainCount]);
    NSArray *nodes = [xdoc selectNodes: @"./items/item"];
    NSLog(@"document retainCount2 = %d", [xdoc retainCount]);
    for (DDXMLElement *tabXmlItem in nodes)
    {
        // here is the parsing
    }
    NSLog(@"document retainCount3 = %d", [xdoc retainCount]);
    [xdoc release];
    [receivedXmlData setLength:0];
    [pool drain];
    [pool release];
}

I see in memory allocator: DDXMLDocuments, DDXMLNodes, DDXMLElements still living after the end of parsing. So, there's big amount of CFString and CFData in the memory. Why these objects aren't cleared? Maybe, I use autorelease pool wrongly or DDXML parser is with surprise?

Answer 1

retainCount is useless. Don't call it. http://whentouseretaincount.com/

No need to both drain and release the pool; just drain it.

Better yet, use @autoreleasepool {...} around the pool's scope.

Since you are using the Allocations instrument, turn on "track reference counts". Then you can look at the history of retains/releases on the objects that are sticking around and see why they are still around.