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


       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.


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