NAME

       MPI_File_read_ordered_begin  -  Reads  a  file  at  a  location specified by a shared file
       pointer; beginning part of a split collective routine (nonblocking).

SYNTAX

C Syntax

       #include <mpi.h>
       int MPI_File_read_ordered_begin(MPI_File fh, void *buf,
            int count, MPI_Datatype datatype)

Fortran Syntax

       USE MPI
       ! or the older form: INCLUDE 'mpif.h'
       MPI_FILE_READ_ORDERED_BEGIN(FH, BUF, COUNT, DATATYPE, IERROR)
            <type>    BUF(*)
            INTEGER   FH, COUNT, DATATYPE, IERROR

Fortran 2008 Syntax

       USE mpi_f08
       MPI_File_read_ordered_begin(fh, buf, count, datatype, ierror)
            TYPE(MPI_File), INTENT(IN) :: fh
            TYPE(*), DIMENSION(..), ASYNCHRONOUS :: buf
            INTEGER, INTENT(IN) :: count
            TYPE(MPI_Datatype), INTENT(IN) :: datatype
            INTEGER, OPTIONAL, INTENT(OUT) :: ierror

C++ Syntax

       #include <mpi.h>
       void MPI::File::Read_ordered_begin(void* buf, int count,
            const MPI::Datatype& datatype)

INPUT/OUTPUT PARAMETER

       fh        File handle (handle).

INPUT PARAMETERS

       count     Number of elements in buffer (integer).

       datatype  Data type of each buffer element (handle).

OUTPUT PARAMETERS

       buf       Initial address of buffer (choice).

       IERROR    Fortran only: Error status (integer).

DESCRIPTION

       MPI_File_read_ordered_begin is the beginning  part  of  a  split  collective,  nonblocking
       routine that must be called by all processes in the communicator group associated with the
       file handle fh.  Each process may pass different argument  values  for  the  datatype  and
       count  arguments. Each process attempts to read, from the file associated with fh, a total
       number of count data items having datatype type into the  user's  buffer  buf.   For  each
       process,  the  location  in  the  file  at which data is read is the position at which the
       shared file pointer would be after all processes whose ranks within  the  group  are  less
       than that of this process had read their data.

NOTES

       All  the  nonblocking  collective  routines for data access are "split" into two routines,
       each with _begin or _end as a suffix. These split collective routines are subject  to  the
       semantic rules described in Section 9.4.5 of the MPI-2 standard.

ERRORS

       Almost all MPI routines return an error value; C routines as the value of the function and
       Fortran routines in the last argument. C++ functions do not return errors. If the  default
       error  handler  is  set  to  MPI::ERRORS_THROW_EXCEPTIONS, then on error the C++ exception
       mechanism will be used to throw an MPI::Exception object.

       Before the error value is returned, the current MPI error handler is called. For  MPI  I/O
       function  errors, the default error handler is set to MPI_ERRORS_RETURN. The error handler
       may   be   changed   with   MPI_File_set_errhandler;   the   predefined   error    handler
       MPI_ERRORS_ARE_FATAL  may  be  used  to  make  I/O  errors  fatal.  Note that MPI does not
       guarantee that an MPI program can continue past an error.