MPI_FILE_WRITE_ALL_BEGIN(3)

💖 MPI_FILE_WRITE_ALL_BEGIN 💖

hii bestie ✨ welcome to the Open MPI page for MPI_FILE_WRITE_ALL_BEGIN(3) — yes that's the whole lowercase-screaming title, we love her. sit down, grab a strawberry 🍓, and let's get into it.

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🎀 NAME 🎀

MPI_File_write_all_begin — Writes a file starting at the locations specified by individual file pointers; beginning part of a split collective routine (nonblocking).

okay so that's a lot of words but basically: it's the beginning half of a two-part nonblocking write situation 💅

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✨ SYNTAX ✨

🦋 C Syntax

#include <mpi.h>

int MPI_File_write_all_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_ALL_BEGIN(FH, BUF, COUNT, DATATYPE, IERROR)
     <type>  BUF(*)
     INTEGER FH, COUNT, DATATYPE, IERROR

🌈 Fortran 2008 Syntax

USE mpi_f08
MPI_File_write_all_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 — File handle (handle). the file we're vibing with.

💜 INPUT PARAMETERS 💜

• buf — Initial address of buffer (choice). where the data lives before we yeet it into the file.
• count — Number of elements in buffer (integer).
• datatype — Data type of each buffer element (handle).

⭐ OUTPUT PARAMETER ⭐

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

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💅 DESCRIPTION 💅

okay so MPI_File_write_all_begin is the beginning part of a split collective, nonblocking routine that attempts to write into the file associated with fh (at the current individual file pointer position maintained by the system) a total number of count data items having datatype type from the user's buffer buf. The data is written into those parts of the file specified by the current view.

not me being the begin half of a dynamic duo 😭 the end half is out there somewhere, and honestly they're giving split collective energy 👑

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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.

bestie please actually read that standard section, i'm not even joking, the split rules are strict and they WILL test you 💀

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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>/MPI_Init_thread <#mpi-init-thread>, after MPI_Finalize <#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 <#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>/MPI_Comm_spawn_multiple <#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.
• 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 <#mpi-abort> was called on that communicator. If called on a window or file, acts as if MPI_Abort <#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 <#mpi-comm-create-errhandler> then MPI_Comm_set_errhandler <#mpi-comm-set-errhandler>
• MPI_File_create_errhandler <#mpi-file-create-errhandler> then MPI_File_set_errhandler <#mpi-file-set-errhandler>
• MPI_Session_create_errhandler <#mpi-session-create-errhandler> then MPI_Session_set_errhandler <#mpi-session-set-errhandler> or at MPI_Session_init <#mpi-session-init>
• MPI_Win_create_errhandler <#mpi-win-create-errhandler> then MPI_Win_set_errhandler <#mpi-win-set-errhandler>

Note that MPI does not guarantee that an MPI program can continue past an error.

See the MPI man page <#open-mpi> for a full list of MPI error codes <#open-mpi-errors>.

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

no cap: if your MPI program errors and you just keep going like nothing happened, that's on you, not on MPI 🙈

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👑 Copyright 👑

2003-2026, The Open MPI Community

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and that's the whole page bestie, you ate that 🫶 this was MPI_FILE_WRITE_ALL_BEGIN(3), straight from Open MPI, dated Sep 10, 2026 — go forth and split your collectives responsibly, mwah 💖✨🎀