gistfile1.txt

static void dispatch_async_repeated_internal(dispatch_time_t firstPopTime, NSTimeInterval intervalInSeconds, dispatch_queue_t queue, void(^work)(BOOL *stop))
{
    dispatch_after(firstPopTime, queue, ^{
        BOOL shouldStop = NO;
        work(&shouldStop);
        if(!shouldStop)
        {
            dispatch_time_t nextPopTime = dispatch_time(DISPATCH_TIME_NOW, (int64_t)(intervalInSeconds * NSEC_PER_SEC));
            dispatch_async_repeated_internal(nextPopTime, intervalInSeconds, queue, work);
        }
    });
}

void dispatch_async_repeated(NSTimeInterval intervalInSeconds, dispatch_queue_t queue, void(^work)(BOOL *stop))
{
    dispatch_time_t firstPopTime = dispatch_time(DISPATCH_TIME_NOW, intervalInSeconds * NSEC_PER_SEC);
    dispatch_async_repeated_internal(firstPopTime, intervalInSeconds, queue, work);
}

There is no need for the __block variable.

And this modification has additional protection against work that takes longer than intervalInSeconds.