I would like to send a user defined data type as:
TYPE CELL
INTEGER :: NUM
TYPE(CELL), POINTER :: NEXT => NULL()
END TYPE CELL
TYPE CELLLIST
INTEGER :: NBCELL
TYPE(CELL), POINTER :: BEGIN => NULL()
END TYPE CELLLIST
and the variable to be sent by MPI is defined as:
TYPE(CELLLIST) :: _CELLLIST
In this variable, _CELLIST%NBCELL denotes the length of the list, and a pointer of type CELL points to the head of the list.
I'd like to use MPI_send and MPI_recv to transfer the cell list via MPI. How to do that?
Sending pointers from one MPI process to another is pointless.
The problem is that they, pointers, are process-specific. It's a reasonable analogy to think of a pointer as storing the memory address of its target. That memory address isn't portable, there is no concept of an address in one process's address space being the same as an address in another process's address space.
You will have to unravel the chain of pointers in your _CELLLIST, send across the CELLS, then rebuild the pointer chain on the target process(es).
I suppose that you might pack the CELLS into an array for transfer. Or you might send one CELL at a time on the understanding that the receiving process(es) will rebuild the dynamic data structure in the order in which it receives the messages containing the CELLs.
