iPhone memory leak in xml parser

krille · 06-20-2009, 07:14 AM

Hi everyone,
I am building an iPhone app that parses a couple of xml files using TouchXML. I have a class XMLParser, which takes care of downloading and parsing the results. I am getting memory leaks when I parse an xml file more than once with the same instance of XMLParser.
Here is one of the parsing methods:

Code:

for(int counter = 0; counter < [item childCount]; counter++) {
	CXMLNode *child = [item childAtIndex:counter];
	if([[child name] isEqualToString:@"PRODUCT"]) 
	{
		NSMutableDictionary *product = [[NSMutableDictionary alloc] 
						init];
		for(int j = 0; j < [child childCount]; j++) {
			CXMLNode *grandchild = [child childAtIndex:j];
			if([[grandchild stringValue] length] > 1) {
				NSString *trimmedString = [[grandchild stringValue] 
				stringByTrimmingCharactersInSet:
				[NSCharacterSet whitespaceAndNewlineCharacterSet]];
				[product setObject:trimmedString 
				forKey:[grandchild name]];
			}
		}
		
		// Add product to current category array
		switch (categoryId) {
			case 0:
				[self.mobil addObject:product];
				break;
			case 1:
				[self.allgemein addObject:product];
				break;
			case 2:
				[self.besitzeIch addObject:product];
				break;
			case 3:
				[self.willIch addObject:product];
				break;
			default:
				break;
		}
		//DebugLog(@"ADD allgemein %@",product);
		[product release];
	}
}

The first time, I parse the xml no leak shows up in instruments, the next time I do so, I got a lot of leaks (NSCFString / NSCFDictionary).
Instruments points me to this line in CXMLNode.m, when I dig into a leaked object:

Code:

theStringValue = [NSString stringWithUTF8String:(const char *)theXMLString];
if ( _node->type != CXMLTextKind )
	xmlFree(theXMLString);
}

return(theStringValue);

I really spent a long time and tried multiple approaches to fix this, but to no avail so far, maybe I am missing something essential?

Any help is highly appreciated, thank you!

krille · 06-20-2009, 11:50 AM

I fixed the problem myself. It is nothing wrong with the TouchXML Code - it was kind of stupid, but maybe someone might come across the same thing, so I am going to post it here.

1) I had a mutable array set up as instance variables like this:

Code:

    @interface XMLParser : NSObject {

    // ...  
    NSMutableArray *mobil;  
    // ...  
    }   
    @property(nonatomic, retain) NSMutableArray *mobil;  
    @end

Everytime I wanted to reset and store new data inside the array I did:

Code:

self.mobil = nil;

Which did not what I wanted to do, so this is the better approach:

Code:

[self.mobil removeAllObjects];

2) The dealloc method has to be like this to fix the leaks (because mobil is defined as a property):

Code:

    -(void)dealloc {  
      [mobil release];  
      self.mobil = nil;  
  }

Whew, that has been a lot of work to find out - hope it saves someone else some time :-)

krish · 11-06-2009, 11:32 AM

Quote:

Originally Posted by krille

I fixed the problem myself. It is nothing wrong with the TouchXML Code - it was kind of stupid, but maybe someone might come across the same thing, so I am going to post it here.

1) I had a mutable array set up as instance variables like this:

Code:

    @interface XMLParser : NSObject {

    // ...  
    NSMutableArray *mobil;  
    // ...  
    }   
    @property(nonatomic, retain) NSMutableArray *mobil;  
    @end

Everytime I wanted to reset and store new data inside the array I did:

Code:

self.mobil = nil;

Which did not what I wanted to do, so this is the better approach:

Code:

[self.mobil removeAllObjects];

2) The dealloc method has to be like this to fix the leaks (because mobil is defined as a property):

Code:

    -(void)dealloc {  
      [mobil release];  
      self.mobil = nil;  
  }

Whew, that has been a lot of work to find out - hope it saves someone else some time :-)

Hi Friend,

I am going through a similar problem. I am also using a custom parser to parse incoming data. But when I check it through Leaks tool, I find the most of the objects I use are leaking. Pleas could you help me?.

Iphoneer · 11-06-2009, 05:33 PM

[quote=krille;95037]

Your dealloc method should include a call to super dealloc. Leaving that off, and it's pretty easy to do, can cause an object to stick around though the retain count for the object is actually zero.

Example dealloc

Code:

    -(void)dealloc {  
      [mobil release];  
      self.mobil = nil;    
      [super dealloc];
  }

krish · 11-09-2009, 07:32 AM

[quote=Iphoneer;140330]

Quote:

Originally Posted by krille

Your dealloc method should include a call to super dealloc. Leaving that off, and it's pretty easy to do, can cause an object to stick around though the retain count for the object is actually zero.

Example dealloc

Code:

    -(void)dealloc {  
      [mobil release];  
      self.mobil = nil;    
      [super dealloc];
  }

Hi Friend, I am using a custom XML parser. But even after releasing it it leaks. Please help me. I have provided the code below:

+(id) requestServiceWithInMemoryContext: (NSManagedObjectContext *)managedObjContext

NSString *)methodName : (NSDictionary *)params : (RequestTypes)requestType
{
NSURL *url=[self getURL: methodName : params];
HWXMLParser *xmlParser = [[HWXMLParser alloc] initWithContext:managedObjContext RequestType:requestType];
NSXMLParser *parser = [[NSXMLParser alloc] initWithContentsOfURL:url];
[parser setDelegate:xmlParser];
[parser setShouldProcessNamespaces:NO];
[parser setShouldReportNamespacePrefixes:NO];
[parser setShouldResolveExternalEntities:NO];
[parser parse];
if ( [parser parserError] ) {
NSLog(@"Parse error %@", [parser parserError]);
if(![HWUtility isNetWorkAvailable])
{
[xmlParser release];
[parser release];
return nil;
}
}
[parser release];
[xmlParser saveManagedObjectContext];
returnValue= [xmlParser getParsedResults];
xmlParser=nil;
[xmlParser release];
return returnValue;
}

The returnValue is

id returnValue;

Thank you..
Krishnan.

BrianSlick · 11-09-2009, 09:24 AM

Code:

HWXMLParser *xmlParser = [[HWXMLParser alloc] initWithContentsOfURL:url];
...
xmlParser=nil;
[xmlParser release];

Release before nil.

Iphoneer · 11-13-2009, 01:41 PM

Quote:

Originally Posted by BrianSlick

Code:

HWXMLParser *xmlParser = [[HWXMLParser alloc] initWithContentsOfURL:url];
...
xmlParser=nil;
[xmlParser release];

Release before nil.

I disagree.

Why send a release message to a pointer that you know points to nil? I know doing so is harmless, but if you are going to use both statements, wouldn't the reverse order be more logical.

BrianSlick · 11-13-2009, 01:43 PM

Quote:

Originally Posted by Iphoneer

I disagree.

Why send a release message to a pointer that you know points to nil? I know doing so is harmless, but if you are going to use both statements, wouldn't the reverse order be more logical.

I think you misread something.

Iphoneer · 11-13-2009, 05:03 PM

Quote:

Originally Posted by BrianSlick

I think you misread something.

Yes, I seemed to have erred...