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.