[petsc-dev] need for HDF5 < 1.8.0 support?

[Smith, Barry F.]

  A potential drawback is some users also use HDF5 directly in their code and may be using an older version (people are very slow to change).

    Barry


> On Dec 7, 2018, at 8:48 AM, Jed Brown via petsc-dev <petsc-dev at mcs.anl.gov> wrote:
> 
> I'm in favor of requiring >=1.8.0.
> 
> Hapla Vaclav via petsc-dev <petsc-dev at mcs.anl.gov> writes:
> 
>> I wanted to add support for HDF5 attributes of groups (currently only datasets).
>> 
>> But I already feel like held back by supporting HDF5 older than 1.8.0. Do we still need that?
>> 
>> My arguments to get rid of that support:
>> 1) It seems we already use some 1.8.0+ functions anyway (might be my fault, though).
>> 2) We could get rid of all those #if
>> 3) There were quite some useful API functions introduced in that release which would make the code simpler. For instance, H5O* functions allow handling groups and datasets the same way.
>> 
>> Ad 2,3 consider this
>> 
>> /* OLD */
>> #if (H5_VERS_MAJOR * 10000 + H5_VERS_MINOR * 100 + H5_VERS_RELEASE >= 10800)
>>  if (dataset) {
>>    PetscStackCallHDF5Return(object, H5Dopen2, (h5, parent, H5P_DEFAULT));
>>  } else if (type == H5O_TYPE_GROUP) {
>>    PetscStackCallHDF5Return(object, H5Gopen2, (h5, parent, H5P_DEFAULT));
>>  }
>> #else
>>  if (dataset) {
>>    PetscStackCallHDF5Return(object, H5Dopen, (h5, parent));
>>  } else if (type == H5O_TYPE_GROUP) {
>>    PetscStackCallHDF5Return(object, H5Gopen, (h5, parent));
>>  }
>> #endif
>> ...
>>  if (dataset) {
>>    PetscStackCallHDF5Return(err, H5Dclose, (object));
>>  } else if (type == H5O_TYPE_GROUP) {
>>    PetscStackCallHDF5Return(err, H5Gclose, (object));
>>  }
>> 
>> 
>> /* NEW */
>>  PetscStackCallHDF5Return(object, H5Oopen, (h5, parent, H5P_DEFAULT));
>>  ...
>>  PetscStackCallHDF5Return(err, H5Oclose, (object));
>> 
>> 
>> Additionally, function H5Oget_info() which can say whether the object is group or dataset was also introduced only in 1.8.0. So the dataset flag above would have to be set by a user it seems...
>> 
>> So I personally think it's already about time to leave the old HDF5 API behind... Objections? If no, I would make a PR which would clean the code from the #ifs and forbid the older versions already in configure.
>> 
>> Vaclav