MPI_FILE_WRITE_AT_ALL(3)

💖 MPI_FILE_WRITE_AT_ALL 💖

okay bestie, gather round, because this is MPI_File_write_at_all from the Open MPI manual (section 3, the library-calls girlies 🫶), and she is Writes a file at explicitly specified offsets (blocking, collective). yes that's the whole vibe. blocking. collective. write-y. slay.

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🎀 SYNTAX 🎀

C Syntax

#include <mpi.h>

int MPI_File_write_at_all(MPI_File fh, MPI_Offset offset, const void *buf,
     int count, MPI_Datatype datatype, MPI_Status *status)

Fortran Syntax

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

Fortran 2008 Syntax

USE mpi_f08
MPI_File_write_at_all(fh, offset, buf, count, datatype, status, ierror)
     TYPE(MPI_File), INTENT(IN) :: fh
     INTEGER(KIND=MPI_OFFSET_KIND), INTENT(IN) :: offset
     TYPE(*), DIMENSION(..), INTENT(IN) :: buf
     INTEGER, INTENT(IN) :: count
     TYPE(MPI_Datatype), INTENT(IN) :: datatype
     TYPE(MPI_Status) :: status
     INTEGER, OPTIONAL, INTENT(OUT) :: ierror

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✨ INPUT PARAMETERS ✨

• fh — the file handle, bestie. (handle)
• offset — the file offset. (integer)
• buf — initial address of your buffer, the lil home of the data. (choice)
• count — how many elements are living in that buffer. (integer)
• datatype — what type each of those buffer elements is. (handle)

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🦋 OUTPUT PARAMETERS 🦋

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

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🌸 DESCRIPTION 🌸

MPI_File_write_at_all is a collective routine — meaning everybody's in on it, no lone wolves here — that attempts to write into the file associated with fh (at the offset position) a total number of count data items, having datatype type, from the user's buffer buf.

The offset is in etype units relative to the current view. Which is to say: holes are not counted when locating an offset. we don't count the gaps, we count the etypes, periodt. 💅

The data gets written into those parts of the file specified by the current view. MPI_File_write_at_all stores the number of datatype elements actually written in status. All other fields of status are undefined — like, do not go looking at them, they contain nothing you should be reading. 🙈

🚨 It is erroneous to call this function if MPI_MODE_SEQUENTIAL mode was specified when the file was opened. erroneous. as in don't. as in not a vibe. as in the whole thing breaks.

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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. (yes, the classic "last arg is the error" situation. iykyk.)

Before that 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.

Now listen — 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. (all of them. everyone. goodbye. 💀)
• 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, it 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, it aborts only the local process.
• MPI_ERRORS_RETURN — returns an error code to the application. polite. considerate. 🫶

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. none.

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!! 💖 copyright vibes from the Open MPI Community, dated Sep 10, 2026, and this was MPI_FILE_WRITE_AT_ALL(3) for Open MPI. go write your file at those explicit offsets collectively and slay. no cap. 🎀✨