[petsc-users] fortran INTENT with petsc object gives segfault after upgrade from 3.8.4 to 3.10.2

[Klaij, Christiaan]

As far as I (mis)understand fortran, this is a data protection
thing: all arguments are passed in from above but the subroutine
is only allowed to change rr and ierr, not aa and xx (if you try,
you get a compiler warning). That's why I find it very odd to
give an intent(in) to rr. But I've tried your suggestion anyway:
both intent(in) and intent(inout) for rr do work! Can't say I
understand though.

Below's a small example of what I was expecting. Change rr to
intent(in) and the compiler complains.

Chris

$ cat intent.f90
program intent

  implicit none

  real, allocatable :: aa(:), xx(:), rr(:)
  integer :: ierr

  allocate(aa(10),xx(10),rr(10))

  aa = 1.0
  xx = 2.0

  call matmult(aa,xx,rr,ierr)

  print *, rr(1)
  print *, ierr

  deallocate(aa,xx,rr)

  contains

    subroutine matmult(aa,xx,rr,ierr)
      real, intent(in) :: aa(:), xx(:)
      real, intent(out):: rr(:)
      integer, intent(out) :: ierr
      rr=aa*xx
      ierr=0
    end subroutine matmult

end program intent
$ ./a.out
   2.000000
           0




dr. ir. Christiaan Klaij  | Senior Researcher | Research & Development
MARIN | T +31 317 49 33 44 | mailto:C.Klaij at marin.nl | http://www.marin.nl

MARIN news: http://www.marin.nl/web/News/News-items/Seminar-Scheepsbrandstof-en-de-mondiale-zwavelnorm-2020.htm

________________________________________
From: Smith, Barry F. <bsmith at mcs.anl.gov>
Sent: Friday, October 19, 2018 2:32 PM
To: Klaij, Christiaan
Cc: petsc-users at mcs.anl.gov
Subject: Re: [petsc-users] fortran INTENT with petsc object gives segfault after upgrade from 3.8.4 to 3.10.2

   Hmm, the intent of all three first arguments should be in since they are passed in from the routine above. Does it work if you replace

>  Vec, INTENT(out) :: rr_system

with

>  Vec, INTENT(in) :: rr_system

?

    Barry


> On Oct 19, 2018, at 3:51 AM, Klaij, Christiaan <C.Klaij at marin.nl> wrote:
>
> I've recently upgraded from petsc-3.8.4 to petsc-3.10.2 and was
> surprised to find a number of segmentation faults in my test
> cases. These turned out to be related to user-defined MatMult and
> PCApply for shell matrices. For example:
>
> SUBROUTINE systemMatMult(aa_system,xx_system,rr_system,ierr)
>  Mat, INTENT(in) :: aa_system
>  Vec, INTENT(in) :: xx_system
>  Vec, INTENT(out) :: rr_system
>  PetscErrorCode, INTENT(out) :: ierr
>  ...
> END
>
> where aa_system is the shell matrix. This code works fine with
> 3.8.4 and older, but fails with 3.10.2 due to invalid
> pointers (gdb backtrace shows failure of VecSetValues due to
> invalid first argument). After replacing by:
>
> SUBROUTINE mass_momentum_systemMatMult(aa_system,xx_system,rr_system,ierr)
>  Mat :: aa_system
>  Vec :: xx_system
>  Vec :: rr_system
>  PetscErrorCode :: ierr
>  ...
> END
>
> everything's fine again. So clearly something has changed since
> 3.8.4 that now prevents the use of INTENT in Fortran (at least
> using intel 17.0.1 compilers). Any reason for this?
>
> Chris
>
>
> dr. ir. Christiaan Klaij  | Senior Researcher | Research & Development
> MARIN | T +31 317 49 33 44 | mailto:C.Klaij at marin.nl | http://www.marin.nl
>
> MARIN news: http://www.marin.nl/web/News/News-items/ReFRESCO-successfully-coupled-to-ParaView-Catalyst-for-insitu-analysis-1.htm
>