[petsc-users] error handling

[Jeremy Theler]

Dear Sam

Probably you are already aware of the following paragraph, but just in
case. Quote from 
https://www.gnu.org/prep/standards/standards.html#Memory-Usage


Memory analysis tools such as valgrind can be useful, but don’t
complicate a program merely to avoid their false alarms. For example,
if memory is used until just before a process exits, don’t free it
simply to silence such a tool. 


Regards
--
jeremy theler
www.seamplex.com



On Tue, 2020-01-21 at 08:49 -0800, Sam Guo wrote:
> I use PETSc from my application. Sounds you are saying I just treat
> ierr!=0 as an system error and no need to call Destroy functions.
> 
> On Tuesday, January 21, 2020, Smith, Barry F. <bsmith at mcs.anl.gov>
> wrote:
> > 
> > > On Jan 20, 2020, at 6:32 PM, Sam Guo <sam.guo at cd-adapco.com>
> > wrote:
> > > 
> > > Hi Barry,
> > >   I understand ierr != 0 means  something catastrophic. I just
> > want to release all memory before I exit PETSc.
> > 
> >    In general not possible. If you run with the debug version and
> > -malloc_debug it is possible but because of the unknown error it
> > could be that the releasing of the memory causes a real crash.
> > 
> >    Is your main concern when you use PETSc for a large problem and
> > it errors because it is "out of memory"?
> > 
> >    Barry
> > 
> > 
> > > 
> > > Thanks,
> > > Sam
> > > 
> > > On Mon, Jan 20, 2020 at 4:06 PM Smith, Barry F. <
> > bsmith at mcs.anl.gov> wrote:
> > > 
> > >   Sam,
> > > 
> > >     I am not sure what your goal is but PETSc error return codes
> > are error return codes not exceptions. They mean that something
> > catastrophic happened and there is no recovery. 
> > > 
> > >     Note that PETSc solvers do not return nonzero error codes on
> > failure to converge etc. You call, for example,
> > KPSGetConvergedReason() after a KSP solve to see if it has failed,
> > this is not a catastrophic failure. If a MatCreate() or any other
> > call returns a nonzero ierr the game is up, you cannot continue
> > running PETSc.
> > > 
> > >    Barry
> > > 
> > > 
> > > > On Jan 20, 2020, at 5:41 PM, Matthew Knepley <knepley at gmail.com
> > > wrote:
> > > > 
> > > > Not if you initialize the pointers to zero: Mat A = NULL.
> > > > 
> > > >    Matt
> > > > 
> > > > On Mon, Jan 20, 2020 at 6:31 PM Sam Guo <sam.guo at cd-adapco.com>
> > wrote:
> > > > I mean MatDestroy.
> > > > 
> > > > On Mon, Jan 20, 2020 at 3:28 PM Sam Guo <sam.guo at cd-adapco.com>
> > wrote:
> > > > Does it hurt to call Destroy function without calling
> > CreateFunction? For example 
> > > > Mat A, B;
> > > > PetscErrorCode  ierr1, ierr2;
> > > > ierr1 = MatCreate(PETSC_COMM_WORLD,&A);
> > > > if(ierr1 == 0)
> > > > {
> > > >   ierr2 = MatCreate(PETSC_COMM_WORLD
> > > > ,&B);
> > > > 
> > > > }
> > > > if(ierr1 !=0 || ierr2 != 0)
> > > > {
> > > >   Destroy(&A);
> > > >   Destroy(&B); // if ierr1 !=0, MatCreat is not called on B.
> > Does it hurt to call Destroy B here?
> > > > }
> > > > 
> > > > 
> > > > 
> > > > On Mon, Jan 20, 2020 at 11:11 AM Dave May <
> > dave.mayhem23 at gmail.com> wrote:
> > > > 
> > > > 
> > > > On Mon 20. Jan 2020 at 19:47, Sam Guo <sam.guo at cd-adapco.com>
> > wrote:
> > > > Can I assume if there is MatCreat or VecCreate, I should clean
> > up the memory myself?
> > > > 
> > > > Yes. You will need to call the matching Destroy function.
> > > > 
> > > > 
> > > > 
> > > > On Mon, Jan 20, 2020 at 10:45 AM Sam Guo <sam.guo at cd-adapco.com
> > > wrote:
> > > > I only include the first few lines of SLEPc example. What about
> > following
> > > >   ierr = MatCreate(PETSC_COMM_WORLD,&A);CHKERRQ(ierr); 
> > > >   ierr =
> > MatSetSizes(A,PETSC_DECIDE,PETSC_DECIDE,n,n);CHKERRQ(ierr);  
> > > > Is there any memory  lost?
> > > > 
> > > > On Mon, Jan 20, 2020 at 10:41 AM Dave May <
> > dave.mayhem23 at gmail.com> wrote:
> > > > 
> > > > 
> > > > On Mon 20. Jan 2020 at 19:39, Sam Guo <sam.guo at cd-adapco.com>
> > wrote:
> > > > I don't have a specific case yet. Currently every call of PETSc
> > is checked. If ierr is not zero, print the error and return. For
> > example,
> > > >    Mat A; /* problem matrix */ 
> > > >    EPS eps; /* eigenproblem solver context */ 
> > > >    EPSType type; 
> > > >   PetscReal error,tol,re,im; 
> > > >   PetscScalar kr,ki; Vec xr,xi; 25 
> > > >   PetscInt n=30,i,Istart,Iend,nev,maxit,its,nconv; 
> > > >   PetscErrorCode ierr; 
> > > >   ierr =
> > SlepcInitialize(&argc,&argv,(char*)0,help);CHKERRQ(ierr); 
> > > >   ierr = PetscOptionsGetInt(NULL,NULL,"-
> > n",&n,NULL);CHKERRQ(ierr);
> > > >    ierr = PetscPrintf(PETSC_COMM_WORLD,"\n1-D Laplacian
> > Eigenproblem, n=%D\n\n",n);CHKERRQ(ierr); 
> > > > 
> > > > I am wondering if the memory is lost by calling CHKERRQ.
> > > > 
> > > > No.
> > > > 
> > > > 
> > > > 
> > > > On Mon, Jan 20, 2020 at 10:14 AM Dave May <
> > dave.mayhem23 at gmail.com> wrote:
> > > > 
> > > > 
> > > > On Mon 20. Jan 2020 at 19:11, Sam Guo <sam.guo at cd-adapco.com>
> > wrote:
> > > > Dear PETSc dev team,
> > > >    If PETSc function returns an error, what's the correct way
> > to clean PETSc?
> > > > 
> > > > The answer depends on the error message reported. Send the
> > complete error message and a better answer can be provided.
> > > > 
> > > > Particularly how to clean up the memory?
> > > > 
> > > > Totally depends on the objects which aren’t being freed. You
> > need to provide more information
> > > > 
> > > > Thanks
> > > > Dave
> > > > 
> > > > 
> > > > Thanks,
> > > > Sam
> > > > 
> > > > 
> > > > -- 
> > > > What most experimenters take for granted before they begin
> > their experiments is infinitely more interesting than any results
> > to which their experiments lead.
> > > > -- Norbert Wiener
> > > > 
> > > > https://www.cse.buffalo.edu/~knepley/
> > > 
> > 
> >