How to manage disk access after splitting the communicator

Hi,

I have been using MPI  succesfully without splitting the group of threads into subgroups. Reading and writing of files have been handled by

a subroutine that allows serial access to the hard disk by the threads (see attached subroutine).

However, as I have an excess of threads for my application, I therefore want to use subgroups by use of  MPI_GROUP_SPLIT. in order

to get an additional speed increase. Can my treatment in the attached subroutine be generalized in some way in order to handle disk access?

Best regards

Anders S