MPI_FILE_IWRITE_AT_ALL(3)

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version 5.0.10 · 7 versions
, in ubuntu stonking

💖 MPI_FILE_IWRITE_AT_ALL 💖

okay bestie, welcome to the Open MPI manual page for MPI_FILE_IWRITE_AT_ALL(3) — it's giving "writing to a file but make it nonblocking AND collective," and honestly? iconic.

🦋 NAME 🦋

MPI_File_iwrite_at_all — writes a file at an explicitly specified offset (nonblocking, collective). yes, it does all three of those things at once. she's versatile 💅

✨ SYNTAX ✨

🌸 C Syntax 🌸

#include <mpi.h>

int MPI_File_iwrite_at_all(MPI_File fh, MPI_Offset offset,
     const void *buf, int count, MPI_Datatype datatype, MPI_Request *request)

🎀 Fortran Syntax 🎀

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

🧚 Fortran 2008 Syntax 🧚

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

🫶 INPUT/OUTPUT PARAMETER 🫶

  • fh — the file handle (handle). it's the little ID card for your file, periodt.

💜 INPUT PARAMETERS 💜

  • offset — the file offset (integer). where in the file we're doing this, bestie.
  • buf — initial address of the buffer (choice). the snack you're handing over to the file.
  • count — number of elements in buffer (integer). how many snacks.
  • datatype — data type of each buffer element (handle). what kind of snack each one is.

🌈 OUTPUT PARAMETERS 🌈

  • request — request object (handle). hold onto this, you'll need it later 👀
  • ierror — Fortran only: error status (integer).

🔥 DESCRIPTION 🔥

MPI_File_iwrite_at_all is the nonblocking version of MPI_File_write_at_all — so like, same energy, but she does NOT wait around. main character behavior honestly.

She 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. and the offset? it's in etype units relative to the current view. which means holes are not counted when locating an offset — so don't go counting your gaps, she doesn't care about them.

The data gets written into those parts of the file specified by the current view. MPI_File_iwrite_at_all stores the number of datatype elements actually written in status — and all other fields of status are undefined, so don't go reading them and expecting lore. there is none.

The request structure can be passed to MPI_Wait or MPI_Test, which will return a status with the number of bytes actually accessed. that's the whole point of the request object, she's the callback queen 💅

🚨 bestie listen. It is erroneous to call this function if MPI_MODE_SEQUENTIAL mode was specified when the file was open. just... don't. it will not go well.

💀 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. classic.

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. (yes that's a lot of words, but every single one is load-bearing 🫠)

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, but make it permanent.
  • 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. she adapts to the situation, we love a flexible queen.
  • MPI_ERRORS_RETURN — returns an error code to the application. the "let me handle it myself" option.

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. that's not a vibe, that's a fact 🙈

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.

2003-2026, The Open MPI Community

okay that's the whole page bestie, you're fully caught up 💖 go forth and iwrite_at_all responsibly. this was the MPI_FILE_IWRITE_AT_ALL(3) page from Open MPI, dated Sep 10, 2026 — thanks for reading, mwah 🎀✨

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