Question

I have a singleton data manager object that manages the connection to a web service, processes the data and then updates a mutable dictionary with the objects. All requests for this dictionary are via this singleton instance that I have created. Now and again I will get conflicts as I am obviously editing a mutable object from many threads and so get the occasional EXC_BAD_ACCESS.

I could implement @synchronized methods or use NSLock but as I am already making extensive use of Grand Central Dispatch I was wondering if there is anything I can do there by forcing them all down one thread synchronously? I also am not sure if the above methods would work and how they would be implemented.

Example code below. The exception can occur in the getObjectArray method as I could be adding to it/updating sub object/deleting in the translateToObjectFromDict method.

NSMutableDictionary *staticDictionary;

-(NSArray *)getObjectArray{

    NSArray *returnArray = [[[NSArray alloc]init]autorelease];
    returnArray = [self.staticDictionary allValues];
    return returnArray;
}

-(void)translateToObjectFromDict:(NSDictionary *)sourceDictionary{



    dispatch_group_t taskGroup = dispatch_group_create();
    dispatch_queue_t queue = dispatch_get_global_queue(0,0);


    dispatch_group_async(taskGroup,queue,^(){

    for (id key in sourceDictionary) {
        NSDictionary *subDictionary = [sourceDictionary objectForKey:key];
        for (id key in subDictionary) {

            NSArray *theObjData = [subDictionary objectForKey:key];
            if ([theObjData count] == 12) {

               theObj *temptheObj = [[PINKtheObj alloc] initWith......
                    NSString *unihex = temptheObj.unihex;

                    if ([self.staticDictionary objectForKey:unihex]){
                        PINKtheObj *localtheObj = [self.staticDictionary objectForKey:unihex];
                        if (temptheObj.time > localtheObj.time) {
                            [localtheObj updatetheObjWith.......
                        [temptheObj release];
                    }else{
                        [self.staticDictionary setObject:temptheObj forKey:unihex];
                    }
            }

        }
    }
    });

    dispatch_group_notify(taskGroup, queue, ^{
        NSDictionary *getMainDict = [self.mainDictionary objectForKey:@"theObjs"];

        for (id key in self.staticDictionary) {
            if (![getMainDict objectForKey:key]){
                [self.removeArray addObject:[self.staticDictionary objectForKey:key]];
            }
        }

        [[NSNotificationCenter defaultCenter]postNotificationName:@"updated" object:nil];
    });
    dispatch_release(taskGroup);

}

Answer 1

I think you should supply all your calls (objectForKey:, setObject:ForKey:, etc.) to your staticDictionary in your own serial queue. Create it when singleton initializes and use everywhere.
In your header file create ivar.

dispatch_queue_t queueDict;

In .m file just add to init

queueDict = dispatch_queue_create("com.yourid.yoursingleton.queueDict ", NULL);

When you want to access or put data into dictionary just make

dispatch_async(queueDict, ^(){
[staticDict setObject:obj forKey:key]; //example
}

You can use dispatch_sync if you want your task to wait for returned value.

__block id returnValue;
dispatch_sync(queueDict, ^(){
returnValue = [statictDict objectForKey:key]; //example
}
obj = returnValue;