MPI_Comm_get_attr(3) MPI MPI_Comm_get_attr(3) NAME MPI_Comm_get_attr - Retrieves attribute value by key SYNOPSIS int MPI_Comm_get_attr(MPI_Comm comm, int comm_keyval, void *attribute_val, int *flag) INPUT PARAMETERS comm - communicator to which the attribute is attached (handle) comm_keyval - key value (integer) OUTPUT PARAMETERS attribute_val - attribute value, unless flag = false (None) flag - false if no attribute is associated with the key (logical) NOTES Attributes must be extracted from the same language as they were inserted in with MPI_ATTR_PUT . The notes for C and Fortran below explain why. THREAD AND INTERRUPT SAFETY This routine is thread-safe. This means that this routine may be safely used by multiple threads without the need for any user-provided thread locks. However, the routine is not interrupt safe. Typically, this is due to the use of memory allocation routines such as malloc or other non-MPICH runtime routines that are themselves not interrupt-safe. NOTES FOR C Even though the attribute_val argument is declared as void * , it is really the address of a void pointer (i.e., a void ** ). Using a void * , how- ever, is more in keeping with C idiom and allows the pointer to be passed without additional casts. NOTES FOR FORTRAN All MPI routines in Fortran (except for MPI_WTIME and MPI_WTICK ) have an additional argument ierr at the end of the argument list. ierr is an inte- ger and has the same meaning as the return value of the routine in C. In Fortran, MPI routines are subroutines, and are invoked with the call state- ment. All MPI objects (e.g., MPI_Datatype , MPI_Comm ) are of type INTEGER in Fortran. The attribute_val in Fortran is a pointer to a Fortran integer, not a pointer to a void * . ERRORS All MPI routines (except MPI_Wtime and MPI_Wtick ) return an error value; C routines as the value of the function and Fortran routines in the last ar- gument. Before the value is returned, the current MPI error handler is called. By default, this error handler aborts the MPI job. The error han- dler may be changed with MPI_Comm_set_errhandler (for communicators), MPI_File_set_errhandler (for files), and MPI_Win_set_errhandler (for RMA windows). The MPI-1 routine MPI_Errhandler_set may be used but its use is deprecated. The predefined error handler MPI_ERRORS_RETURN may be used to cause error values to be returned. Note that MPI does not guarantee that an MPI program can continue past an error; however, MPI implementations will attempt to continue whenever possible. MPI_SUCCESS - No error; MPI routine completed successfully. MPI_ERR_ARG - Invalid argument. Some argument is invalid and is not identified by a specific error class (e.g., MPI_ERR_RANK ). MPI_ERR_COMM - Invalid communicator. A common error is to use a null communica- tor in a call (not even allowed in MPI_Comm_rank ). MPI_ERR_KEYVAL - Invalid keyval MPI_ERR_OTHER - Other error; use MPI_Error_string to get more information about this error code. 4/10/2026 MPI_Comm_get_attr(3)
NAME | SYNOPSIS | INPUT PARAMETERS | OUTPUT PARAMETERS | NOTES | THREAD AND INTERRUPT SAFETY | NOTES FOR C | NOTES FOR FORTRAN | ERRORS
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