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 * , however, 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  integer  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 statement.

       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 argument.  Before the value  is
       returned,  the current MPI error handler is called.  By default, this error handler aborts
       the MPI  job.   The  error  handler  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  communicator  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.

                                            2/22/2022                        MPI_Comm_get_attr(3)