MPI_FILE_WRITE_ORDERED_BEGIN(3)

💖 MPI_FILE_WRITE_ORDERED_BEGIN(3) 💖

okay bestie, sit DOWN, because this one is from the Open MPI manual and it's giving "collective I/O but make it nonblocking, split, and ordered" ✨

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🌸 NAME 🌸

MPI_File_write_ordered_begin — writes a file at a location specified by a shared file pointer; it's the beginning part of a split collective routine (and it's nonblocking, no cap).

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✨ SYNTAX ✨

🎀 C Syntax

#include <mpi.h>

int MPI_File_write_ordered_begin(MPI_File fh, const void *buf,
    int count, MPI_Datatype datatype)

🎀 Fortran Syntax

USE MPI
! or the older form: INCLUDE 'mpif.h'

MPI_FILE_WRITE_ORDERED_BEGIN(FH, BUF, COUNT, DATATYPE, IERROR)
    <type>  BUF(*)
    INTEGER FH, COUNT, DATATYPE, IERROR

🎀 Fortran 2008 Syntax

USE mpi_f08

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

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🦋 INPUT/OUTPUT PARAMETER 🦋

• fh — the file handle, bestie. (handle)

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🌈 INPUT PARAMETERS 🌈

• buf — initial address of buffer (choice). yes it's a choice, we love options 💅
• count — number of elements in buffer (integer).
• datatype — data type of each buffer element (handle).

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🍓 OUTPUT PARAMETER 🍓

• ierror — Fortran only: error status (integer).

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👑 DESCRIPTION 👑

MPI_File_write_ordered_begin is the beginning part of a split collective, nonblocking routine, and it must be called by every single process in the communicator group associated with the file handle fh. Like, all of them. Group project rules fr fr.

Each process may pass different argument values for the datatype and count arguments — nobody has to match, it's not that kind of party.

After all processes of the group have issued their respective calls, each process attempts to write, into the file associated with fh, a total number of count data items having datatype type contained in the user's buffer buf.

And here's the ordered part, the main character twist: for each process, the location in the file at which data is written 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 written their data. so everyone queues up by rank, no skipping, no cutting 🙈

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📝 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. iykyk 📚

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💀 ERRORS 💀

Almost all MPI routines return an error value; C routines as the return result of the function and Fortran routines in the last argument.

Before the error value is returned, the current MPI error handler associated with the communication object (e.g., communicator, window, file) is called. If no communication object is associated with the MPI call, then the call is considered attached to MPI_COMM_SELF and will call the associated MPI error handler. When MPI_COMM_SELF is not initialized (i.e., before MPI_Init/MPI_Init_thread, after MPI_Finalize, or when using the Sessions Model exclusively) the error raises the initial error handler. The initial error handler can be changed by calling MPI_Comm_set_errhandler on MPI_COMM_SELF when using the World model, or the mpi_initial_errhandler CLI argument to mpiexec or info key to MPI_Comm_spawn/MPI_Comm_spawn_multiple. If no other appropriate error handler has been set, then the MPI_ERRORS_RETURN error handler is called for MPI I/O functions and the MPI_ERRORS_ABORT error handler is called for all other MPI functions.

Open MPI includes three predefined error handlers that can be used:

• MPI_ERRORS_ARE_FATAL — causes the program to abort all connected MPI processes. dramatic much 😭
• MPI_ERRORS_ABORT — an error handler that can be invoked on a communicator, window, file, or session. When called on a communicator, it acts as if MPI_Abort was called on that communicator. If called on a window or file, acts as if MPI_Abort was called on a communicator containing the group of processes in the corresponding window or file. If called on a session, aborts only the local process.
• MPI_ERRORS_RETURN — returns an error code to the application.

MPI applications can also implement their own error handlers by calling:

• MPI_Comm_create_errhandler then MPI_Comm_set_errhandler
• MPI_File_create_errhandler then MPI_File_set_errhandler
• MPI_Session_create_errhandler then MPI_Session_set_errhandler or at MPI_Session_init
• MPI_Win_create_errhandler then MPI_Win_set_errhandler

⚠️ note that MPI does not guarantee that an MPI program can continue past an error. like, that's it, that's the run. 🫶

See the MPI man page for a full list of MPI error codes.

See the Error Handling section of the MPI-3.1 standard for more information.

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📜 Copyright

2003-2026, The Open MPI Community

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and that's the whole page bestie, you ate it, periodt 💅✨ this was Open MPI, MPI_FILE_WRITE_ORDERED_BEGIN(3), dated Sep 10, 2026 — go forth and write things in order, love u 🦋💖