Need to return data from a completion block that is called in the same method

Question

I have a delegate class that needs to return data for certain methods. My problem is that some of the calls that I make to get that data are async (using completion blocks), so it's difficult to return from the method with the data in hand. Here is what I came up with:

- (NSArray *)contentsAtPath:(NSString *)path
{
    __block NSMutableArray *contentsArray = [NSMutableArray array];
    __block BOOL blockProcessing = YES;

    SuccessBlock success = ^(MyResult *result)
    {            
        for (NSUInteger i = 0; i < result.count; i++)
        {
            MyItem *item = [result objectAtIndex:i];
            [contentsArray addObject:item];
        }

        blockProcessing = NO;
    };

    [self.dataManager itemsAtPath:path success:success failure:nil];

    while (blockProcessing) {
        // wait for block to complete
    }

    return contentsArray;
}

Is there any better way to achieve this without having the while loop?

Answer 1

Sure. Something like this might work:

- (NSArray *)contentsAtPath:(NSString *)path
{
    NSMutableArray *contentsArray = [NSMutableArray array];

    dispatch_semaphore_t sem = dispatch_semaphore_create(0);

    SuccessBlock success = ^(MyResult *result)
    {
        for (NSUInteger i = 0; i < result.count; i++)
        {
            MyItem *item = [result objectAtIndex:i];
            [contentsArray addObject:item];
        }

        dispatch_semaphore_signal(sem);
    };

    [self.dataManager itemsAtPath:path success:success failure:nil];

    dispatch_semaphore_wait(sem, DISPATCH_TIME_FOREVER);

    // If not ARC then
    // [sem release];

    return contentsArray;
}

Also note that regardless, contentsArray does not need the __block specifier (at least for the code here).