[petsc-users] How to check NULL pointer in Fortran

[袁煕]

Awesome, thanks! I'll check it out.

Yuan

2021年11月27日(土) 1:56 Barry Smith <bsmith at petsc.dev>:

>
>   I believe I have fixed the bug in the branch
> *barry/2021-11-26/fix-petscsfgetgraph-fortran/release *
> https://gitlab.com/petsc/petsc/-/merge_requests/4605
>
>   See src/vec/is/sf/tutorials/ex1f.F90 for how to check if the returned
> value is a FORTRAN_NULL_INTEGER
>
>   Barry
>
>
> On Nov 24, 2021, at 3:19 AM, 袁煕 <yuanxi at advancesoft.jp> wrote:
>
> Thank you for the clarification.  I am looking forward to this bug fix.
>
> Yuan
>
> 2021年11月22日(月) 23:17 Barry Smith <bsmith at petsc.dev>:
>
>>
>>    The address of PETSC_NULL_INTEGER is not 0, it in some common block
>> location. PETSC_NULL_INTEGER should not be used in the form
>> if idx == PETSC_NULL_INTEGER, it is only to be used as an argument to a
>> PETSc function that on the C side can take a NULL (integer) argument.
>>
>>    As I noted before whoever wrote the incorrect petscsfgetgraph_ Fortran
>> wrapper needs to fix it.
>>
>>   Barry
>>
>>
>> On Nov 21, 2021, at 8:05 PM, 袁煕 <yuanxi at advancesoft.jp> wrote:
>>
>> Thank you very much.
>>
>> The NULL pointer could be identified by if(
>> loc(gmine)==PETSC_NULL_INTEGER) as above @Mark Adams <mfadams at lbl.gov> suggested.
>> However, It seems that there is a memory leak here?
>>
>> Yuan
>>
>> 2021年11月19日(金) 22:20 Barry Smith <bsmith at petsc.dev>:
>>
>>>
>>>   it is very possible there is a bug in the Fortran interface for this
>>> function. It looks like whoever wrote the Fortran interface did not think
>>> through the special case of contiguous entries.
>>>
>>> PETSC_EXTERN void  petscsfgetgraph_(PetscSF *sf,PetscInt
>>> *nroots,PetscInt *nleaves, F90Array1d  *ailocal, F90Array1d  *airemote,
>>> PetscErrorCode *ierr PETSC_F90_2PTR_PROTO(pilocal)
>>> PETSC_F90_2PTR_PROTO(piremote))
>>> {
>>>   const PetscInt    *ilocal;
>>>   const PetscSFNode *iremote;
>>>
>>>   *ierr = PetscSFGetGraph(*sf,nroots,nleaves,&ilocal,&iremote);if
>>> (*ierr) return;
>>>   *ierr = F90Array1dCreate((void*)ilocal,MPIU_INT,1,*nleaves, ailocal
>>> PETSC_F90_2PTR_PARAM(pilocal));
>>>   /* this creates a memory leak */
>>>   f90arraysfnodecreate_((PetscInt*)iremote,nleaves, airemote
>>> PETSC_F90_2PTR_PARAM(piremote));
>>> }
>>>
>>> PetscErrorCode F90Array1dCreate(void *array,MPI_Datatype type,PetscInt
>>> start,PetscInt len,F90Array1d *ptr PETSC_F90_2PTR_PROTO(ptrd))
>>> {
>>>   PetscFunctionBegin;
>>>   if (type == MPIU_SCALAR) {
>>>     if (!len) array = PETSC_NULL_SCALAR_Fortran;
>>>     f90array1dcreatescalar_(array,&start,&len,ptr
>>> PETSC_F90_2PTR_PARAM(ptrd));
>>>   } else if (type == MPIU_REAL) {
>>>     if (!len) array = PETSC_NULL_REAL_Fortran;
>>>     f90array1dcreatereal_(array,&start,&len,ptr
>>> PETSC_F90_2PTR_PARAM(ptrd));
>>>   } else if (type == MPIU_INT) {
>>>     if (!len) array = PETSC_NULL_INTEGER_Fortran;
>>>     f90array1dcreateint_(array,&start,&len,ptr
>>> PETSC_F90_2PTR_PARAM(ptrd));
>>>   } else if (type == MPIU_FORTRANADDR) {
>>>     f90array1dcreatefortranaddr_(array,&start,&len,ptr
>>> PETSC_F90_2PTR_PARAM(ptrd));
>>>   } else SETERRQ(PETSC_COMM_SELF,PETSC_ERR_SUP,"Unsupported
>>> MPI_Datatype");
>>>   PetscFunctionReturn(0);
>>> }
>>>
>>> It blindly calls F90Array1dCreate() with a len = *nleaves > 0 but a NULL
>>> array ilocal then f90array1dcreateint_ must create an invalid object.
>>>
>>> Barry
>>>
>>>
>>>
>>> > On Nov 19, 2021, at 12:34 AM, 袁煕 <yuanxi at advancesoft.jp> wrote:
>>> >
>>> > Dear PETSc-team,
>>> >
>>> > I am using function PetscSFGetGraph in my program like
>>> > -----------------------
>>> > call PetscSFGetGraph(sf,gnroots,gnleaves,gmine,gremote,ierr)
>>> > -----------------------
>>> >
>>> > In some cases, it works well. But in some cases, I encountered
>>> following error
>>> > ------------------
>>> > PETSC ERROR: Caught signal number 11 SEGV: Segmentation Violation,
>>> probably memory access out of range
>>> > ------------------
>>> > I found it is due to the action of reading gmine, which is a fortran
>>> pointer point to an array. It is reasonable because PETSc manual tells me
>>> "if returned value is NULL, it means leaves are in contiguous storage". The
>>> problem is that I cannot find if gmine is a null pointer.
>>> > 1)  I cannot use "if (gmine==PETSC_NULL_INTEGER)" because my intel
>>> compiler would return a compile error "A scalar-valued expression is
>>> required in this context"
>>> > 2)  When using standard style of checking a null pointer in fortran,
>>> "associated(gmine)", it returns "T". Even in cases such action of "print *,
>>> gmine(1)" would give rise to above Segmentation Violation error.
>>> > Is there any means to check the NULL pointer in Fortran in above cases.
>>> > Many thanks,
>>> > Yuan
>>>
>>>
>>
>
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