NAME

       MPI_Grequest_start -  Create and return a user-defined request

SYNOPSIS

       int MPI_Grequest_start( MPI_Grequest_query_function *query_fn,
                             MPI_Grequest_free_function *free_fn,
                             MPI_Grequest_cancel_function *cancel_fn,
                             void *extra_state, MPI_Request *request )

INPUT PARAMETERS

       query_fn
              - callback function invoked when request status is queried (function)
       free_fn
              - callback function invoked when request is freed (function)
       cancel_fn
              - callback function invoked when request is cancelled (function)
       extra_state
              - Extra state passed to the above functions.

OUTPUT PARAMETERS

       request
              - Generalized request (handle)

NOTES ON THE CALLBACK FUNCTIONS

       The  return  values  from  the callback functions must be a valid MPI error code or class.
       This value may either be the return value from any MPI routine (with one  exception  noted
       below) or any of the MPI error classes.  For portable programs, MPI_ERR_OTHER may be used;
       to provide more  specific  information,  create  a  new  MPI  error  class  or  code  with
       MPI_Add_error_class or MPI_Add_error_code and return that value.

       The  MPI  standard is not clear on the return values from the callback routines.  However,
       there are notes in the standard that imply that these are MPI error codes.   For  example,
       pages  169  line  46 through page 170, line 1 require that the free_fn return an MPI error
       code that may be used in the MPI completion functions when they return MPI_ERR_IN_STATUS .

       The one special case is the error  value  returned  by  MPI_Comm_dup  when  the  attribute
       callback  routine  returns a failure.  The MPI standard is not clear on what values may be
       used to indicate an error return.  Further, the Intel MPI test suite made use of  non-zero
       values  to  indicate failure, and expected these values to be returned by the MPI_Comm_dup
       when the attribute routines encountered an error.  Such error values may not be valid  MPI
       error  codes  or  classes.  Because of this, it is the user's responsibility to either use
       valid MPI error codes in return from the attribute callbacks, if those error codes are  to
       be  returned by a generalized request callback, or to detect and convert those error codes
       to valid MPI error codes (recall that MPI error classes are valid error codes).

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 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.

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  guarentee 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 ).

                                            11/12/2016                      MPI_Grequest_start(3)