iOS - NJSONSerialization causing a memory leak??(according to Instruments)

Question

Below is the method with the code, where I am getting a memory leak using manual memory management. The memory leak is detected by using Xcode instruments and specifically points to the line where I am using NSJSONSerialization. I am running the target app (on a device with iOS 6.1).

The first time that i tap on the refreshButton there is no leak. Any subsequent tap generates the leak(and more leaks on top of that if i continue tapping the button). Below is the code - This is basic stuff for consuming JSON web services(the web service link is bogus but the real one that I am using works). You will notice that I am using Grand Central Dispatch so that I can update the UI without waiting for the parsing of the JSON to finish.

The line detected by instruments is surrounded by the asterisks. I would like to get some help to anyone who might have an idea of what is going on here. The full stack trace(as mentioned in the below comments i will put here:)

+(NSJSONSerialization JSONObjectWithData:option:error:] -> -[_NSJSONReader parseData:options:] -> -[_NSJSONReader parseUTF8JSONData:skipBytes:options]->newJSONValue->newJSONString->[NSPlaceholde‌​rString initWithBytes:length:encoding:]

-(void)parseDictionary:(NSDictionary *)dictonary{

self.transactions = [dictonary objectForKey:@"transactions"];
if(!self.transactions){
    NSLog(@"Expected 'transactions' array");
    return;
}

for (int arrayIndex = 0; arrayIndex < [self.transactions count]; arrayIndex++) {
    TransactionResult *result = [[[TransactionResult alloc] init] autorelease];
    result.transactionID = [[self.transactions objectAtIndex:arrayIndex] objectForKey:@"ID"];
    result.transactionDescription = [[self.transactions objectAtIndex:arrayIndex] objectForKey:@"description"];
    result.transactionPrice = [[self.transactions objectAtIndex:arrayIndex] objectForKey:@"price"];
    self.totalPrice += [result.transactionPrice doubleValue];
    NSLog(@"total price: %f", self.totalPrice);
    [self.transactionResults addObject:result];
    result = nil;
}

}

 - (IBAction)refreshButtonPressed:(UIBarButtonItem *)sender {
        __block id resultObject;
        dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0),^{
        NSURL *url = [NSURL URLWithString:@"http://mywebservice.php"];
        NSData *data = [NSData dataWithContentsOfURL:url];

        NSError *error;
        ***resultObject = [NSJSONSerialization JSONObjectWithData:data options:NSJSONReadingAllowFragments error:&error];***

        if(!error){
            if([resultObject isKindOfClass:[NSDictionary class]]){
                NSDictionary *dictonary = resultObject;
                [self parseDictionary:dictonary];
                NSLog(@"Done parsing!");
                dispatch_async(dispatch_get_main_queue(), ^{
                    self.isLoading = NO;
                    [self.transactionsTableView reloadData];
                });
            }
            else{
                NSLog(@"JSON Error: Expected Dictionary");
                resultObject = nil;
                return;
            }
        }
        else{
            NSLog(@"JSON Error: %@", [error localizedDescription]);
            dispatch_async(dispatch_get_main_queue(), ^{
                resultObject = nil;
                [self.transactionsTableView reloadData];
                [self showError];
            });
            return;
        }
    });
    }

Answer 1

I used a ARC as soon as it came out with 4.3, and put an app in the store with it - point being you could switch to ARC. That said, I tried to reproduce your problem by creating a class/file that has the no-arc flag applied to it, but cannot reproduce the problem. This makes me believe your problem is elsewhere. In the code below, I create a Test object in another file, retain it, and send it the test message. No matter what I set "i" to, it always deallocs the object:

#import "Tester.h"

@interface Obj : NSObject <NSObject>
@end

@implementation Obj

- (id)retain
{
    NSLog(@"retain");
    id i = [super retain];
    return i;
}

- (oneway void)release
{
    NSLog(@"release");
    [super release];
}

- (void)foo
{

}

- (void)dealloc
{
    NSLog(@"Obj dealloced");
    [super dealloc];
}

@end

@implementation Tester

- (void)test
{
    int i = 2;

    __block Obj *obj;

    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0),^{
        obj = [[Obj new] autorelease];

        if(i == 0) {
            Obj *o = obj;
            dispatch_async(dispatch_get_main_queue(), ^
                {
                    [o foo];
                } );
        } else if(i == 1) {
            obj = nil;
        } else if(i == 2) {
            dispatch_async(dispatch_get_main_queue(), ^
                {
                    obj = nil;
                } );
        }
    } );

}

@end