dispatch_queue_t for concurrent use.

ConcurrentQueue_Objc.m

@interface className()
//create a property  as dispatch_queue_t
@property (nonatomic) dispatch_queue_t concurrentQueue;
@end

@implementation className

//implement a lazy initializer 

- (dispatch_queue_t)concurrentQueue
{
    static dispatch_once_t __dispatchToken = 0;
    const char *queueAddress = "com.company.domain.concurrent";
    dispatch_queue_attr_t attr = dispatch_queue_attr_make_with_qos_class(DISPATCH_QUEUE_CONCURRENT, QOS_CLASS_USER_INITIATED, 2);
    /**
    * the trick goes here to declear it as [id] so it could be dispatched_once
    * meaning we don't create it over and over again if we need to do multiple dispatch_async 
    */
    static id queue;
    dispatch_once(&__dispatchToken, ^{
        queue = dispatch_queue_create(queueAddress, attr);
    });
    
    return queue;
}

//Usage
- (void)performingSeriesOfTaskMethodName
{
    __weak typeof(self)weakSelf = self;
    dispatch_async(self.concurrentQueue, ^{
        __strong typeof(weakSelf)strongSelf = weakSelf;
        [strongSelf runYourMethodsInSideTheBlock];
        //Always remember to update the main queue after you long task
    });
}

@end