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MPIX_Comm_shrink

: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

#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

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

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

.. seealso::
   * :ref:`MPIX_Comm_is_revoked`