MPI_FILE_WRITE_AT_ALL_BEGIN(3)

💅 MPI_FILE_WRITE_AT_ALL_BEGIN(3) — the Open MPI glow-up

okay so bestie, buckle in, because this is a page from the Open MPI manual and it's about writing to files in parallel like the main character you are. no cap, this one's a split collective and the name is a whole mouthful, but we're gonna get through it together 🫶

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✨ SYNTAX ✨

C Syntax (the classic 💖)

#include <mpi.h>

int MPI_File_write_at_all_begin(MPI_File fh, MPI_Offset offset,
     const void *buf, int count, MPI_Datatype datatype)

Fortran Syntax (yes, including the old-school form 🎀)

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

Fortran 2008 Syntax (the fancy modern one, honestly iconic 🌸)

USE mpi_f08
MPI_File_write_at_all_begin(fh, offset, buf, count, datatype, ierror)
     TYPE(MPI_File), INTENT(IN) :: fh
     INTEGER(KIND=MPI_OFFSET_KIND), INTENT(IN) :: offset
     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, aka your little backstage pass to the file (handle).

💜 INPUT PARAMETERS 💜

• offset — where in the file we're writing, babes (handle).
• buf — initial address of the buffer, your data's home base (choice).
• count — how many elements are chilling in that buffer (integer).
• datatype — the data type of each buffer element (handle).

🌈 OUTPUT PARAMETER 🌈

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

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👑 DESCRIPTION 👑

MPI_File_write_at_all_begin is literally the beginning part of a split collective — meaning it's a nonblocking routine that attempts to write into the file associated with fh (at the offset position) a total number of count data items, having datatype datatype, from the user's buffer buf. slay 💅

the offset is in etype units relative to the current view. that's the important bit, bestie — holes are not counted when locating an offset. the data gets written into those parts of the file specified by the current view. periodt.

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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. 😭
• 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, no promises bestie 🙈

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 💖 giving you everything, keeping every single detail, not a crumb left behind. this one's brought to you by the Open MPI girlies, dated Sep 11, 2026 — go forth and write at those explicit offsets, you absolute icon 👑✨