MPI_TYPE_CREATE_KEYVAL(3)

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version 5.0.10 · 7 versions
, in ubuntu stonking

💖 MPI_TYPE_CREATE_KEYVAL 💖

okay bestie, so this one is from the Open MPI manual, section 3, and it's literally called MPI_TYPE_CREATE_KEYVAL(3). not me showing up with the keyval generator for datatypes?? we love a niche little utility. let's get into it 🌸

✨ NAME ✨

MPI_Type_create_keyval — generates a new attribute key for caching on data types.

like, it makes you a fresh key so you can stash attribute stuff on datatypes, periodt 💅

✨ SYNTAX ✨

🎀 C Syntax

#include <mpi.h>

int MPI_Type_create_keyval(MPI_Type_copy_attr_function *type_copy_attr_fn,
     MPI_Type_delete_attr_function *type_delete_attr_fn,
     int *type_keyval, void *extra_state)

🎀 Fortran Syntax

USE MPI
! or the older form: INCLUDE 'mpif.h'
MPI_TYPE_CREATE_KEYVAL(TYPE_COPY_ATTR_FN, TYPE_DELETE_ATTR_FN,
             TYPE_KEYVAL, EXTRA_STATE, IERROR)
     EXTERNAL TYPE_COPY_ATTR_FN, TYPE_DELETE_ATTR_FN
     INTEGER TYPE_KEYVAL, IERROR
     INTEGER(KIND=MPI_ADDRESS_KIND) EXTRA_STATE

🎀 Fortran 2008 Syntax

USE mpi_f08
MPI_Type_create_keyval(type_copy_attr_fn, type_delete_attr_fn, type_keyval,
             extra_state, ierror)
     PROCEDURE(MPI_Type_copy_attr_function) :: type_copy_attr_fn
     PROCEDURE(MPI_Type_delete_attr_function) :: type_delete_attr_fn
     INTEGER, INTENT(OUT) :: type_keyval
     INTEGER(KIND=MPI_ADDRESS_KIND), INTENT(IN) :: extra_state
     INTEGER, OPTIONAL, INTENT(OUT) :: ierror

✨ INPUT PARAMETERS ✨

  • type_copy_attr_fn — the copy callback function for type_keyval (it's a function, girlies, you gotta hand it a whole function).
  • type_delete_attr_fn — the delete callback function for type_keyval (also a function, yes another one).
  • extra_state — extra state for the callback functions. little care package for your callbacks 🎁

✨ OUTPUT PARAMETERS ✨

  • type_keyval — the key value for future access (integer). keep it safe, you'll be using it later 💖
  • ierror — Fortran only: error status (integer).

✨ DESCRIPTION ✨

so MPI_Type_create_keyval generates a new attribute key for caching on data types. this routine partially replaces MPI_Keyval_create. key word: partially, bestie, don't @ me 😭

the argument type_copy_attr_fn may be specified as MPI_TYPE_NULL_COPY_FN or MPI_TYPE_DUP_FN from C or Fortran.

  • MPI_TYPE_NULL_COPY_FN is a function that does nothing other than returning flag = 0 and MPI_SUCCESS. it's giving minimal effort, and honestly? valid.
  • MPI_TYPE_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. lowkey just parrots the value back, and it ate.

the argument type_delete_attr_fn may be specified as MPI_TYPE_NULL_DELETE_FN from C or Fortran. MPI_TYPE_NULL_DELETE_FN is a function that does nothing beyond returning MPI_SUCCESS. truly the "no thoughts, head empty, still successful" icon 👑

the C callback functions are:

typedef int MPI_Type_copy_attr_function(MPI_Datatype oldtype,
            int type_keyval, void *extra_state, void *attribute_val_in,
            void *attribute_val_out, int *flag);

typedef int MPI_Type_delete_attr_function(MPI_Datatype type, int type_keyval,
             void *attribute_val, void *extra_state);

the Fortran callback functions are:

SUBROUTINE TYPE_COPY_ATTR_FN(OLDTYPE, TYPE_KEYVAL, EXTRA_STATE,
             ATTRIBUTE_VAL_IN, ATTRIBUTE_VAL_OUT, FLAG, IERROR)
    INTEGER OLDTYPE, TYPE KEYVAL, IERROR
    INTEGER(KIND=MPI_ADDRESS_KIND) EXTRA_STATE,
        ATTRIBUTE_VAL_IN, ATTRIBUTE_VAL_OUT
    LOGICAL FLAG

SUBROUTINE TYPE_DELETE_ATTR_FN(TYPE, TYPE_KEYVAL, ATTRIBUTE_VAL, EXTRA_STATE,
             IERROR)
    INTEGER TYPE, TYPE_KEYVAL, IERROR
    INTEGER(KIND=MPI_ADDRESS_KIND) ATTRIBUTE VAL, EXTRA_STATE

✨ ERRORS ✨

almost all MPI routines return an error value, bestie. C routines hand it back as the return result of the function, and Fortran routines tuck it into the last argument. that's just how it is 🤷

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. like, it escalates, and it's a whole thing.

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

  • MPI_ERRORS_ARE_FATAL — causes the program to abort all connected MPI processes. dramatic much? yes. on purpose 💀
  • 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

DIY energy, we respect it 🫶

note that MPI does not guarantee that an MPI program can continue past an error. so like, don't just vibe through it and assume everything's fine. it might not be, fr fr.

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_Type_free_keyval

2003-2026, The Open MPI Community

and that's the whole page, bestie 💜 this was MPI_TYPE_CREATE_KEYVAL(3), dated Sep 10, 2026, served fresh from the Open MPI manual. go make some datatype keys, you icon 👑✨ bye!!

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