NSMutableArray+QueueAdditions.m

#import "NSMutableArray+QueueAdditions.h"

// Nader Rahimizad, Added Thread safety for inset and remove operations
static char const * const serialQueueKey = "serialQueueKey";

// http://stackoverflow.com/questions/12098011/objective-c-is-nsmutablearray-thread-safe
// http://oleb.net/blog/2011/05/faking-ivars-in-objc-categories-with-associative-references/

@implementation NSMutableArray (QueueAdditions) 
@dynamic objectTag;

- (id)serialQueue {
    return objc_getAssociatedObject(self, serialQueueKey);
}

- (void)setSerialQueue:(id)newObjectTag {
    objc_setAssociatedObject(self, serialQueueKey, newObjectTag, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
}


- (id)objectAtIndex:(NSUInteger)index {
    __block id obj;

	if(self.serialQueue == nil)
		self.serialQueue = dispatch_queue_create("com.NSMutableArrayQueueAdditions.SerialQueue", NULL);

	dispatch_barrier_async(self.serialQueue, ^{
		obj = [self.searchResult objectAtIndex:index];
	});

    return obj;
}

- (void)removeObjectAtIndex:(NSUInteger)index {

	if(self.serialQueue == nil)
		self.serialQueue = dispatch_queue_create("com.NSMutableArrayQueueAdditions.SerialQueue", NULL);

	dispatch_barrier_async(self.serialQueue, ^{
		[self.searchResult removeObjectAtIndex:index];
	});
}

- (void)insertObject:(id)obj atIndex:(NSUInteger)index {

	if(self.serialQueue == nil)
		self.serialQueue = dispatch_queue_create("com.NSMutableArrayQueueAdditions.SerialQueue", NULL);

    dispatch_barrier_async(self.serialQueue, ^{
        [self.searchResult insertObject:obj atIndex:index];
    });
}

- (void)appendObject:(id)obj{

	if(self.serialQueue == nil)
		self.serialQueue = dispatch_queue_create("com.NSMutableArrayQueueAdditions.SerialQueue", NULL);

    dispatch_barrier_async(self.serialQueue, ^{
        [self.searchResult addObject:obj];
    });
}


// Add to the tail of the queue
-(void) enqueue: (id) anObject {
	 concurrent_queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);

    // Push the item in
    [self addObject: anObject];
}

// Grab the next item in the queue, if there is one
-(id) dequeue {
    // Set aside a reference to the object to pass back
    id queueObject = nil;
    
    // Do we have any items?
    if ([self lastObject]) {
        // Pick out the first one
#if !__has_feature(objc_arc)
        queueObject = [[[self objectAtIndex: 0] retain] autorelease];
#else
        queueObject = [self objectAtIndex: 0];
#endif
        // Remove it from the queue
        [self removeObjectAtIndex: 0];
    }
    
    // Pass back the dequeued object, if any
    return queueObject;
}

// Takes a look at an object at a given location
-(id) peek: (int) index {
    // Set aside a reference to the peeked at object
    id peekObject = nil;
    // Do we have any items at all?
    if ([self lastObject]) {
        // Is this within range?
        if (index < [self count]) {
            // Get the object at this index
            peekObject = [self objectAtIndex: index];
        }
    }
	
    // Pass back the peeked at object, if any
    return peekObject;
}

// Let's take a look at the next item to be dequeued
-(id) peekHead {
    // Peek at the next item
	return [self peek: 0];
}

// Let's take a look at the last item to have been added to the queue
-(id) peekTail {
    // Pick out the last item
	return [self lastObject];
}

// Checks if the queue is empty
-(BOOL) empty {
    return ([self lastObject] == nil);
}

@end