--- name: "MPI_Comm_create_keyval" section: "3" platform: "linux" package: "openmpi" version: "5.0.11-1" release: "Arch Linux 2026-11-01" platforms: ["linux"] url: "https://new.carta.tech/MPI_Comm_create_keyval" --- # MPI\_Comm\_create\_keyval(3) *MPI\_Comm\_create\_keyval* — Generates a new attribute key. ## SYNTAX ### C Syntax ``` #include 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) ``` ### Fortran Syntax ``` 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 ``` ### Fortran 2008 Syntax ``` 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 ``` ## INPUT PARAMETERS - • - **comm\_copy\_attr\_fn** Copy callback function for **comm\_keyval** (function). - • - **comm\_delete\_attr\_fn** Delete callback function for **comm\_keyval** (function). - • **extra\_state** : Extra state for callback functions. ## OUTPUT PARAMETER - • **comm\_keyval** : Key value for future access (integer). - • **ierror** : Fortran only: Error status (integer). ## DESCRIPTION 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 ``` ## 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:** - • *MPI\_Comm\_free\_keyval* ## COPYRIGHT 2003-2026, The Open MPI Community