[petsc-users] Is PetscViewerBinary special?

[Dave May]

Thanks Matt.

Given the PETSc way of doing things, I believe the following should be
possible:
[1] attach an option prefix to a viewer
[2] skip the header on some binary viewers
[3] use mpiio for some binary viewers, but not all of them.

However, it doesn't appear to be completely simple to allow this behaviour.

For instance, replacing
    ierr =
PetscOptionsGetBool(NULL,"-viewer_binary_mpiio",&useMPIIO,NULL);CHKERRQ(ierr);
with
    ierr =
PetscOptionsGetBool(((PetscObject)viewer)->prefix,"-viewer_binary_mpiio",&useMPIIO,NULL);CHKERRQ(ierr);
won't work as an option prefix will never have been set.

If I was to add a PetscViewerSetFromOptions_Binary(), I would have to
ensure that PetscViewerSetFromOptions() was called before
PetscViewerFileSetName() was called as the latter this triggers a swap of
the functions used to open binary file, e.g. from
PetscViewerFileSetName_Binary() to PetscViewerFileSetName_MPIIO()

Would it be simpler and cleaner to have MPIIO be defined as an independent
implementation which was a sub-class of the binary class?

Then we could use command line flags to switch between implementations at
runtime
  -xxx_viewer_type binary
versus
  -xxx_viewer_type mpiio
rather than having to use
  -xxx_viewer_type binary -viewer_binary_mpiio
which has obvious short comings like forcing all binary viewers,
independent of the prefix to use mpiio. It would also allow the PetscViewer
object to be used in a manner which follows the standard PETSc pattern of:
XXCreate(), XXSetOptionsPrefix(), XXSetType(), XXSetFromOptions().

Then we could do this
  PetscViewerCreate()
  PetscViewerSetOptionsPrefix()
  PetscViewerSetType()
  PetscViewerFileSetMode()
  PetscViewerBinarySetSkipHeader()
  PetscViewerFileSetName()
  PetscViewerSetFromOptions()
and it wouldn't matter which order SetName(), BinarySkipHeader() etc were
called.

What do people think?


Cheers
  Dave





On 30 January 2015 at 13:56, Matthew Knepley <knepley at gmail.com> wrote:

> On Fri, Jan 30, 2015 at 2:06 AM, Dave May <dave.mayhem23 at gmail.com> wrote:
>
>> Hello,
>>
>> I've noticed the create function PetscViewerCreate_Binary() doesn't
>> appear to be using the options prefix attached to the PetscViewer.
>> Specifically, I see on line 1276 of
>>   petsc-3.5.2/src/sys/classes/viewer/impls/binary/binv.c
>> the following
>>   ierr =
>> PetscOptionsGetBool(NULL,"-viewer_binary_mpiio",&useMPIIO,NULL);CHKERRQ(ierr);
>>
>> Is this an oversight or something intentional?
>>
>
> This is an oversight.
>
>   Matt
>
>
>> Are PetscViewers in general behaving such that they cannot be configured
>> independently of each other if
>> PetscViewerSetOptionsPrefix() and PetscViewerSetFromOptions() are called?
>>
>>
>> Cheers
>>   Dave
>>
>
>
>
> --
> 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
>
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