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  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 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.

       MPIX_Comm_ishrink  is the non-blocking variant of MPIX_Comm_shrink.  Note that, as with 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  MPIX_Comm_shrink  and  MPIX_Comm_ishrink  are maintained when comm is revoked, or when the
       group of comm contains failed MPI processes. In particular, MPIX_Comm_shrink  and  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

       Almost  all  MPI  routines  return  an  error  value; C routines as the return result of the function and
       Fortran routines in the last argument.

       Before the error value is returned, the current MPI  error  handler  associated  with  the  communication
       object  (e.g.,  communicator, window, file) is called.  If no communication object is associated with the
       MPI call, then the call is considered attached to MPI_COMM_SELF and will call the  associated  MPI  error
       handler.   When   MPI_COMM_SELF   is   not  initialized  (i.e.,  before  MPI_Init/MPI_Init_thread,  after
       MPI_Finalize, or when using the Sessions Model exclusively) the error raises the initial  error  handler.
       The  initial  error handler can be changed by calling MPI_Comm_set_errhandler on MPI_COMM_SELF when using
       the World model, or the mpi_initial_errhandler CLI argument to mpiexec or info  key  to  MPI_Comm_spawn/‐
       MPI_Comm_spawn_multiple.   If no other appropriate error handler has been set, then the MPI_ERRORS_RETURN
       error handler is called for MPI I/O functions and the MPI_ERRORS_ABORT error handler is  called  for  all
       other MPI functions.

       Open MPI includes three predefined error handlers that can be used:

       • MPI_ERRORS_ARE_FATAL Causes the program to abort all connected MPI processes.

       • MPI_ERRORS_ABORT An error handler that can be invoked on a communicator, window, file, or session. When
         called  on  a  communicator,  it  acts  as if MPI_Abort was called on that communicator. If called on a
         window or file, acts as if MPI_Abort was called on a communicator containing the group of processes  in
         the corresponding window or file. If called on a session, aborts only the local process.

       • MPI_ERRORS_RETURN Returns an error code to the application.

       MPI applications can also implement their own error handlers by calling:

       • MPI_Comm_create_errhandler then MPI_Comm_set_errhandler

       • MPI_File_create_errhandler then MPI_File_set_errhandler

       • MPI_Session_create_errhandler then MPI_Session_set_errhandler or at MPI_Session_init

       • MPI_Win_create_errhandler then MPI_Win_set_errhandler

       Note that MPI does not guarantee that an MPI program can continue past an error.

       See the MPI man page for a full list of MPI error codes.

       See the Error Handling section of the MPI-3.1 standard for more information.

       SEE ALSO:

          • MPIX_Comm_is_revoked

COPYRIGHT

       2003-2025, The Open MPI Community

                                                  Feb 17, 2025                               MPIX_COMM_SHRINK(3)