DOKK / manpages / debian 13 / openmpi-doc / MPI_Comm_create_keyval.openmpi.3.en
MPI_COMM_CREATE_KEYVAL(3) Open MPI MPI_COMM_CREATE_KEYVAL(3)

MPI_Comm_create_keyval — Generates a new attribute key.

#include <mpi.h>
int MPI_Comm_create_keyval(MPI_Comm_copy_attr_function


    *comm_copy_attr_fn, MPI_Comm_delete_attr_function


    *comm_delete_attr_fn, int *comm_keyval,


    void *extra_state)



USE MPI
! or the older form: INCLUDE 'mpif.h'
MPI_COMM_CREATE_KEYVAL(COMM_COPY_ATTR_FN, COMM_DELETE_ATTR_FN,


    COMM_KEYVAL, EXTRA_STATE, IERROR)


    EXTERNAL COMM_COPY_ATTR_FN, COMM_DELETE_ATTR_FN


    INTEGER COMM_KEYVAL, IERROR


    INTEGER(KIND=MPI_ADDRESS_KIND) EXTRA_STATE



USE mpi_f08
MPI_Comm_create_keyval(comm_copy_attr_fn, comm_delete_attr_fn, comm_keyval,


        extra_state, ierror)


    PROCEDURE(MPI_Comm_copy_attr_function) :: comm_copy_attr_fn


    PROCEDURE(MPI_Comm_delete_attr_function) :: comm_delete_attr_fn


    INTEGER, INTENT(OUT) :: comm_keyval


    INTEGER(KIND=MPI_ADDRESS_KIND), INTENT(IN) :: extra_state


    INTEGER, OPTIONAL, INTENT(OUT) :: ierror


•
(function).

•
comm_keyval (function).

•
extra_state : Extra state for callback functions.

  • comm_keyval : Key value for future access (integer).
  • ierror : Fortran only: Error status (integer).

This function replaces MPI_Keyval_create, the use of which is deprecated. The C binding is identical. The Fortran binding differs in that extra_state is an address-sized integer. Also, the copy and delete callback functions have Fortran bindings that are consistent with address-sized attributes. The argument comm_copy_attr_fn may be specified as MPI_COMM_NULL_COPY_FN or MPI_COMM_DUP_FN from C or Fortran. MPI_COMM_NULL_COPY_FN is a function that does nothing more than returning flag = 0 and MPI_SUCCESS. MPI_COMM_DUP_FN is a simple-minded copy function that sets flag = 1, returns the value of attribute_val_in in attribute_val_out, and returns MPI_SUCCESS. These replace the MPI-1 predefined callbacks MPI_NULL_COPY_FN and MPI_DUP_FN, the use of which is deprecated. The two C callback functions are:

typedef int MPI_Comm_copy_attr_function(MPI_Comm oldcomm, int comm_keyval,


             void *extra_state, void *attribute_val_in,


             void *attribute_val_out, int *flag);
typedef int MPI_Comm_delete_attr_function(MPI_Comm comm, int comm_keyval,


             void *attribute_val, void *extra_state);


which are the same as the MPI-1.1 calls but with a new name. The old names are deprecated. The two Fortran callback functions are:

SUBROUTINE COMM_COPY_ATTR_FN(OLDCOMM, COMM_KEYVAL, EXTRA_STATE,


             ATTRIBUTE_VAL_IN, ATTRIBUTE_VAL_OUT, FLAG, IERROR)


    INTEGER OLDCOMM, COMM_KEYVAL, IERROR


    INTEGER(KIND=MPI_ADDRESS_KIND) EXTRA_STATE, ATTRIBUTE_VAL_IN,


        ATTRIBUTE_VAL_OUT


    LOGICAL FLAG
SUBROUTINE COMM_DELETE_ATTR_FN(COMM, COMM_KEYVAL, ATTRIBUTE_VAL, EXTRA_STATE,


             IERROR)


    INTEGER COMM, COMM_KEYVAL, IERROR


    INTEGER(KIND=MPI_ADDRESS_KIND) ATTRIBUTE_VAL, EXTRA_STATE


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:

•
MPI_Comm_free_keyval



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February 17, 2025