MPI_Comm_get_attr(3)

NAME
     MPI_Comm_get_attr - Retrieves a communicator attribute value by key

SYNOPSIS
     C:

          #include <mpi.h>

          int MPI_Comm_get_attr ( comm, comm_keyval, attribute_val, flag )
          MPI_Comm comm;
          int comm_keyval;
          void *attribute_val;
          int *flag;


     Fortran:

          INCLUDE "mpif.h" (or USE MPI)

          INTEGER comm, comm_keyval, ierror
          INTEGER(KIND=MPI_ADDRESS_KIND) attribute_val
          LOGICAL flag

          CALL MPI_COMM_GET_ATTR(comm, comm_keyval, attribute_val,
          flag, ierror)


STANDARDS
     This function is defined in the MPI-2 standard.

     This release implements the MPI 1.2 standard, as documented by the MPI
     Forum in the spring 1997 release of MPI:  A Message Passing Interface
     Standard.

DESCRIPTION
     The MPI_Comm_get_attr routine retrieves a communicator attribute value by
     key.  This function replaces MPI_Attr_get, whose use is deprecated.  This
     routine accepts the following parameters:

     comm      Specifies the communicator to which the attribute is attached
               (handle).

     comm_keyval
               Specifies the key value (integer).

     attribute_val
               Returns the attribute value, unless flag is set to false.

     flag      Specifies the presence of an attribute value.  If an attribute
               value was extracted, flag is set to true.  If no attribute is
               associated with the key, flag is set to false.
     ierror    Specifies the return code value for successful completion,
               which is in MPI_SUCCESS.  MPI_SUCCESS is defined in the mpif.h
               file.

NOTES
     Attributes must be extracted from the same language as that in which they
     were inserted.

     For C programs, even though the attribute_val argument is declared as
     void, it is really the address of a void pointer.  See the standard for
     more details.

     For Fortran programs, the attribute_val is a pointer to a Fortran integer
     of kind MPI_ADDRESS_KIND, not a pointer to a void.  Note this is
     different from the deprecated function MPI_Attr_get.

ENVIRONMENTAL INQUIRIES
     MPI predefines the following attributes attached to MPI_COMM_WORLD.
     These attributes may not be deleted, their keys freed, nor their values
     changed.

     MPI_TAG_UB
          Upper bound for tag value.

     MPI_HOST
          Host process rank, if such exists, otherwise MPI_PROC_NULL.

     MPI_IO
          Rank of a node that has regular I/O facilities.  Nodes in the same
          communicator may return different valus for this parameter.

     MPI_WTIME_IS_GLOBAL
          Boolean variable that indicates whether clocks are synchronized.

SEE ALSO
      MPI_Attr_delete(3), MPI_Attr_put(3), MPI_Keyval_create(3)

     Section 7.1.1 of the MPI-1.2 Standard for more discussion of the
     environmental inquiries.