MPI_FILE_WRITE_SHARED(3)

👑 MPI_FILE_WRITE_SHARED 👑

okay so bestie, we're deep in the Open MPI manual and this page is MPI_FILE_WRITE_SHARED(3). what does it do? it writes a file using the shared file pointer, and it's blocking and noncollective. that's the whole vibe check. 🦋

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📝 SYNTAX 📝

three flavors, pick ur fighter:

🩷 C Syntax

#include <mpi.h>

int MPI_File_write_shared(MPI_File fh, 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_SHARED(FH, BUF, COUNT, DATATYPE, STATUS, IERROR)
    <type>  BUF(*)
      INTEGER   FH, COUNT, DATATYPE, STATUS(MPI_STATUS_SIZE), IERROR

🩶 Fortran 2008 Syntax

USE mpi_f08

MPI_File_write_shared(fh, buf, count, datatype, status, ierror)
    TYPE(MPI_File), INTENT(IN) :: fh
    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/OUTPUT PARAMETER 🔁

• fh — the file handle (handle). literally ur ticket to the file, bestie 🎀

📥 INPUT PARAMETERS 📥

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

📤 OUTPUT PARAMETERS 📤

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

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💅 DESCRIPTION 💅

so MPI_File_write_shared is a blocking routine that uses the shared file pointer to write files. iconic behavior honestly.

but here's the tea, and it's important tea: the order of serialization is not deterministic for this noncollective routine. not me reminding u twice. 🙈

bestie listen — not deterministic. don't go building ur whole app on the assumption that things land in a cute little order. they do not. 🔥

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🚨 ERRORS 🚨

almost all MPI routines return an error value, and where it shows up depends on ur language: C routines return it as the return result of the function, and Fortran routines put it in the last argument. periodt.

Before the error value is returned, the current MPI error handler associated with the communication object (like a communicator, a window, or a file, iykyk) 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. And 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. That initial error handler can be changed by calling MPI_Comm_set_errhandler on MPI_COMM_SELF when you're using the World model, or by 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, 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.

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

heads up bestie: MPI does not guarantee that an MPI program can continue past an error. 😭 no cap.

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 🫶 this was MPI_FILE_WRITE_SHARED(3) from Open MPI, straight outta the Sep 10, 2026 build. go forth and write some files, but remember the serialization order is chaos. slay. ✨🎀🌈