Hello,
Again, I think things are mixed up a bit here. Therefore again the facts.
First you must distinguish between internal and external sessions:
- An internal session is a memory area for program execution inside an external session. It is opened in a call sequence when one program calls another with CALL TRANSACTION or SUBMIT AND RETRUN. The maximum number of internal sessions in a call sequence is 9 (see Calling ABAP Programs).
- An external session or main session is connected to an user session. The maximum number of external sessions for one user session is 16 but it is normally restricted to 6 by profile parameter rdisp/max_alt_modes (see Main Session).
These facts also hold for parallel processing with CALL FUNCTION STARTING NEW TASK.
Here you must distinguish between called program and calling program:
- In the called program you can open new internal and external sessions as long as the above limits are not exceeded (this is why in your above example the called function module cannot open more than 6 sessions for the RFC user).
- In the calling program you can also open new internal and external sessions as long as the above limits are not exceeded. Only if you are working with callback routines you should not open new internal sessions in the calling program, because the callback routines will not be found any more when the called function module has finished (that was what the original question was about).
These facts should be enough to explain the observed behavior.