Deprecate mpif.h and freeze the mpi module

[mpiforumbot]

Originally by jsquyres on 2014-02-04 07:44:19 -0600

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OvereviewThe mpif.h interface has many limitations and is not recommended. Let's deprecate it in MPI 4.0.

Similarly, the mpi module has many limitations -- but at least it's better than mpif.h, and gives users an easy-upgrade path for their existing mpif.h-based applications. Let's freeze the mpi module interface in MPI 4.0.

The mpi_f08 module is the Way Forward, but it forces a larger change to existing MPI applications. Plus, not all compilers support the technology needed to properly implement the entire mpi_f08 module. So let's not force all applications to go to the mpi_f08 module yet.

However, let's not let future Forum discussions be bound by the old Fortran limitations.

SolutionThis ticket:

1. Deprecates the mpif.h interface. No new interfaces will be aded to the mpif.h interface (note that we already actively discouraged its use in MPI-3.0).
2. Freezes the mpi interface. As stated above, the mpi module is better than mpif.h, but it still has many limitations. Let's not advance it any further.
3. Since this ticket adds a "The entire mpif.h interface has been deprecated..." blurb in the deprecated chapter, this ticket also renames the deprecated chapter from "Deprecated Functions" to "Deprecated Interfaces".

The idea is that the Forum should be able to move forward with the most modern version of Fortran so that we don't have to keep having "Well, what about Fortran?" moments.

Note: the attached PDF is labeled as "MPI 3.1" on the front page, but only because it was made from the 3.1 latex tree. This ticket is aimed at MPI 4.0.

Impact on existing implementationsNone. You can still keep your mpif.h interface and your mpi module.

(...but you better start implementing that mpi_f08 module if you haven't already done so!)

[mpiforumbot]

Originally by jsquyres on 2014-02-04 07:52:57 -0600

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Attachment added: mpi-report-mpifh-deprecated-mpi-frozen-2014-02-4.pdf (2702.6 KiB)

[mpiforumbot]

Originally by jsquyres on 2014-03-04 19:29:48 -0600

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Due to scheduling, I ended up reading this ticket today instead of tomorrow morning.

• As probably could be predicted, the Forum didn't particularly like the concept of freezing the mpi module. See the straw vote, below.
  • The point was made that we'll be encouraging people to leave mpif.h and go to the mpi module, but we'll be freezing the mpi module.
  • What's the point? That doesn't seem attractive to users at all.
• There is overwhelming support for deprecating mpif.h.
  • A strong point was made that we will need to advertise this change very carefully to the mpif.h community to ensure that the correct message is put out:
  • We're deprecating the mpif.h module, not removing it
  • This signals that we may remove it in the future, but we're not removing it any time soon
  • Users can easily migrate existing code to the mpi module, but really would benefit from fully upgrading to the mpi_f08 module

Here's the straw votes we took on this ticket:

1. mpif.h: Deprecate:14, Freeze:0, Maintain:0, Abstain:5
   • This is pretty clear support for deprecating the mpif.h interface.
2. mpi module: Deprecate:7, Freeze:0, Maintain:7, Abstain:4
   • This is not strong support at all.

[mpiforumbot]

Originally by RolfRabenseifner on 2014-12-10 16:43:41 -0600

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Straw vote at the Dec. 2014 forum meeting on deprecating mpif.h: 23 Yes, 1 No, 2 Abstain.