The Functional Developer ORB has one request processing thread per POA, by default. You can set the number of request processing threads when creating a POA by using the thread policy, for example:
thread-policy: 4
This creates a pool of worker 4 threads that service requests dispatched to that POA. Therefore, up to 4 requests could be processed concurrently. In such a situation the underlying application code that is called from the POA must be multi-thread safe.