C# and C++ communication

Question

Container (written in C#) provides all the basic functionality (connects to database, sends order to exchange, subscribes market data etc).

 

Service (written in C++) would use this container.

 

One interface has been implemented in container with this functionality (event callbacks, sending orders, sending alerts, liveness) and it’s used by service.

 

Both service and container are running on different process.

 

Communication: Service will send request to container to provide some data. Container has to call the callback function with data.

 

How should service communicate to container? How does container send the callback to service as both are running on different process?