在Fortran中使用MPI_Gather时，无效的指针和分段错误

Question

I have a simple program, which is supposed to gather a number of small arrays into one big one using MPI.

PROGRAM main 
    include 'mpif.h' 

    integer ierr, i, myrank, thefile, n_procs
    integer, parameter          :: BUFSIZE = 3
    complex*16, allocatable    :: loc_arr(:), glob_arr(:)

    call MPI_INIT(ierr) 
    call MPI_COMM_RANK(MPI_COMM_WORLD, myrank, ierr) 
    call MPI_COMM_SIZE(MPI_COMM_WORLD, n_procs, ierr)

    allocate(loc_arr(BUFSIZE))
    loc_arr = 0.7 * myrank - cmplx(0.3, 0, kind=8)


    allocate(glob_arr(n_procs* BUFSIZE))

    write (*,*) myrank, shape(glob_arr)

    call MPI_Gather(loc_arr, BUFSIZE, MPI_DOUBLE_COMPLEX,&
                    glob_arr, n_procs * BUFSIZE, MPI_DOUBLE_COMPLEX,&
                    0, MPI_COMM_WORLD, ierr)
    write (*,*) myrank,"Errorcode:" , ierr
    call MPI_FINALIZE(ierr) 

END PROGRAM main

I have some experience with MPI in C, but for Fortran 90 nothing seems to work. Here is how I compile(I use ifort) and run it:

 mpif90 test.f90 -check all && mpirun -np 4 ./a.out
           1          12
           3          12
           3 Errorcode:           0
           1 Errorcode:           0
           0          12
           2          12
           2 Errorcode:           0
           0 Errorcode:           0
*** Error in `./a.out': free(): invalid pointer: 0x0000000000a25790 ***

===================================================================================
=   BAD TERMINATION OF ONE OF YOUR APPLICATION PROCESSES
=   PID 10889 RUNNING AT LenovoX1kabel
=   EXIT CODE: 6
=   CLEANING UP REMAINING PROCESSES
=   YOU CAN IGNORE THE BELOW CLEANUP MESSAGES
===================================================================================

===================================================================================
=   BAD TERMINATION OF ONE OF YOUR APPLICATION PROCESSES
=   PID 10889 RUNNING AT LenovoX1kabel
=   EXIT CODE: 6
=   CLEANING UP REMAINING PROCESSES
=   YOU CAN IGNORE THE BELOW CLEANUP MESSAGES
===================================================================================

What do I do wrong? Sometimes I will get this pointer problem, sometimes I will a segmentation fault, but to me it doesn't look like any of the ifort checks complain.

All the Errorcodes are 0, so I'm not sure where I go wrong.

Answer 1

You should never specify the number of processes in MPI collectives. That is a simple rule of thumb.

Therefore the line n_procs * BUFSIZE is clearly wrong.

And indeed the manual states that: recvcount Number of elements for any single receive (integer, significant only at root).

You should just use BUFSIZE . This is the same for C and Fortran.