GCD Semaphore for finding items around you based on distance

GCD Semaphore

NSArray *stores = ...;
CLLocation *myLocation = ...;

NSMutableArray *nearestStores = [NSMutableArray array];
CLRegion *nearest100kmRegion = [CLRegion initCircularRegionWithCenter:[myLocation coordinate]
                                                               radius:100000
                                                           identifier:@"someIdentifier"];

// We will need to enumerate all stores to ensure that there are no more
// than 25 objects within the defined region.
//
// Since there may be thousands of objects and many of them can be
// out of the defined region, we should perform concurrent enumeration
// for performance reasons.
dispatch_semaphore s = dispatch_semaphore_create(1);
[stores enumerateObjectsWithOptions:NSEnumerationConcurrent
                         usingBlock:^(id store, NSUInteger idx, BOOL *stop)
{
     if ([nearest100kmRegion containsCoordinate:[[store location] coordinate]])
     {
         dispatch_semaphore_wait(s, DISPATCH_FOREVER);
         [nearestStores addObject:store];
         dispatch_semaphore_signal(s);
     }
}];
dispatch_release(s);

if ([nearestStores count] > 25)
{
    [nearestStores sortWithOptions:NSSortConcurrent
                   usingComparator:^(id store1, id store2)
    {
        return [myLocation distanceFromLocation:[store1 location]] - [myLocation distanceFromLocation:[store2 location]];
    }];
}

return [nearestStores subarrayWithRange:NSMakeRange(0, MAX([nearestStores count], 25))];