It's a very broad question - inter process communication is potentially very complicated, and you've a variety of methods and approaches. Just remember - synchronizing two processes to pass data is 'expensive' in terms of processor time, so it's better if you can think of a way to do it asynchronously. But you've also got to be careful to watch for locking between the two. So the answer is always 'it depends'.

In addition to what's already been mentioned - you might want to consider running threads, and using thread-level data transfer. threads::shared, Thread::Queue, Thread::Semaphore are possibilities.