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.. _mpix_comm_shrink:
MPIX_Comm_shrink
================
.. include_body
:ref:`MPIX_Comm_shrink`, :ref:`MPIX_Comm_ishrink` - Create a new communicator
that includes all processes from the parent communicator that have not failed.
This is part of the User Level Fault Mitigation :ref:`ULFM extension <ulfm-label>`.
SYNTAX
------
C Syntax
^^^^^^^^
.. code-block:: c
#include <mpi.h>
#include <mpi-ext.h>
int MPIX_Comm_shrink(MPI_Comm comm, MPI_Comm *newcomm)
int MPIX_Comm_ishrink(MPI_Comm comm, MPI_Comm *newcomm, MPI_Request *request)
Fortran Syntax
^^^^^^^^^^^^^^
.. code-block:: fortran
USE MPI
USE MPI_EXT
! or the older form: INCLUDE 'mpif.h'
MPIX_COMM_SHRINK(COMM, NEWCOMM, IERROR)
INTEGER COMM, NEWCOMM, IERROR
MPIX_COMM_ISHRINK(COMM, NEWCOMM, REQUEST, IERROR)
INTEGER COMM, NEWCOMM, REQUEST, IERROR
Fortran 2008 Syntax
^^^^^^^^^^^^^^^^^^^
.. code-block:: fortran
USE mpi_f08
USE mpi_ext_f08
MPIX_Comm_shrink(comm, newcomm, ierror)
TYPE(MPI_Comm), INTENT(IN) :: comm
TYPE(MPI_Comm), INTENT(OUT) :: newcomm
INTEGER, OPTIONAL, INTENT(OUT) :: ierror
MPIX_Comm_ishrink(comm, newcomm, request, ierror)
TYPE(MPI_Comm), INTENT(IN) :: comm
TYPE(MPI_Comm), INTENT(OUT), ASYNCHRONOUS :: newcomm
TYPE(MPI_Request), INTENT(OUT) :: request
INTEGER, OPTIONAL, INTENT(OUT) :: ierror
INPUT PARAMETERS
----------------
* ``comm``: Communicator (handle).
OUTPUT PARAMETERS
-----------------
* ``newcomm``: Communicator (handle).
* ``request``: Request (handle, non-blocking only).
* ``ierror``: Fortran only: Error status (integer).
DESCRIPTION
-----------
This collective operation creates a new intra- or intercommunicator
*newcomm* from the intra- or intercommunicator *comm*, respectively, by
excluding the group of failed MPI processes as shrinkd upon during the
operation.
The groups of *newcomm* must include every MPI process that returns from
:ref:`MPIX_Comm_shrink`, and it must exclude every MPI process whose failure
caused an operation on *comm* to raise an MPI error of class
MPIX_ERR_PROC_FAILED or MPIX_ERR_PROC_FAILED_PENDING at a member of the
groups of *newcomm*, before that member initiated the shrink operation.
Said otherwise, this procedure is semantically equivalent to an
:ref:`MPI_Comm_split` operation that would succeed despite failures, where
members of the groups of *newcomm* participate with the same color and a key
equal to their rank in *comm*.
:ref:`MPIX_Comm_ishrink` is the non-blocking variant of :ref:`MPIX_Comm_shrink`.
Note that, as with :ref:`MPI_Comm_idup`, it is erroneous to use *newcomm*
before *request* has completed.
WHEN THE COMMUNICATOR IS REVOKED OR CONTAINS FAILED PROCESSES
-------------------------------------------------------------
This function never raises an error of classes MPIX_ERR_REVOKED or
MPIX_ERR_PROC_FAILED. The defined semantics of :ref:`MPIX_Comm_shrink` and
:ref:`MPIX_Comm_ishrink` are maintained when *comm* is revoked, or when the
group of *comm* contains failed MPI processes. In particular,
:ref:`MPIX_Comm_shrink` and :ref:`MPIX_Comm_ishrink` are collective operations,
even when *comm* is revoked.
The implementation will strive to detect all failures during the shrink
operation, but in certain circumpstances, the group of *newcomm* may still
contain failed MPI processes, whose failure will be detected in subsequent
MPI operations on *newcomm*.
ERRORS
------
.. include:: ./ERRORS.rst
.. seealso::
* :ref:`MPIX_Comm_is_revoked`
|
