Why does coarray with allocatable component creates segmentation faults when accessed from different image?

Question

I want to use the fortran coarray feature to have different size arrays on different images.

Following the 2008/2018 standard, this should be possible by using a derived type containing an allocatable. I am using gfortran 8.2.0 with opencoarrays 2.3.1.1 MPI library on macOS Mojave.

program Main
    implicit none

    type :: Array_Type
        double precision, dimension(:), allocatable :: values
    end type
    type(Array_Type), codimension[*] :: array

    if(this_image() == 1) then
        allocate(array%values(2))
        array%values = this_image()
    else
        allocate(array%values(1))
    endif
    sync all

    print *, this_image(), array[1]%values(:)
    sync all
end program

The program is compiled by

gfortran -Wall -fcoarray=lib Main.f90 -lcaf_mpi

An even simpler example leads to the same segmentation fault when the allocated array is accessed by other images.

program Main
    implicit none

    type :: Array_Type
        double precision, dimension(:), allocatable :: values
    end type
    type(Array_Type), codimension[*] :: array

    allocate(array%values(2))
    sync all

    print *, this_image(), array[1]%values(:)
    sync all
end program

I would file an issue in the OpenCoarray github. Either it is a bug and they should know about it or you will get a qualified explanation. Your codes works for me with Intel Fortran 16. — Vladimir F
What's the expected behavior for the print statement in the second code block? Isn't array[1]%values undefined when it's not yet assigned a value? — knia
@A. Hennonk: It is not initialized, but the space in memory is defined. It might contain any value, but for printing the value is not important. — Frenz

Frenz Frenz · Accepted Answer · 2019-01-14T16:03:40

Solution

The code works correctly with the specified system as long as MPICH instead of the default OpenMpi is used with OpenCoarrays.

Additionally, the OpenCoarrays compiler wrapper should be used: caf Main.f90

I opened an issue at the OpenCoarrays GitHub site: https://github.com/sourceryinstitute/OpenCoarrays/issues/625

Why does coarray with allocatable component creates segmentation faults when accessed from different image?

1 Answers