[petsc-users] error handling

[Smith, Barry F.]

> 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/
>