MPI_FILE_IWRITE_AT(3)

📦
version 5.0.10 · 7 versions
, in ubuntu stonking

💖 MPI_File_iwrite_at 💖

hiiii bestie 🫶 welcome to the MPI_FILE_IWRITE_AT(3) page, straight out of the Open MPI manual ✨ it's giving "write to a file, but at a spot you pick, and also don't wait around for it" 💅

MPI_File_iwrite_at — Writes a file at an explicitly specified offset (nonblocking, noncollective).

like yes, that's the whole vibe: you say WHERE, you say WHAT, and it does NOT block you. queen behavior honestly 👑

✨ SYNTAX ✨

🌸 C Syntax

#include <mpi.h>

int MPI_File_iwrite_at(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(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(fh, offset, buf, count, datatype, request, 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
     TYPE(MPI_Request), INTENT(OUT) :: request
     INTEGER, OPTIONAL, INTENT(OUT) :: ierror

🔄 INPUT/OUTPUT PARAMETER

  • fh — File handle (handle). this is your file's little ID card bestie, it's how everyone knows WHICH file we're talking about 🎀

📥 INPUT PARAMETERS

  • offset — File offset (integer). where in the file we're dropping the data 📍
  • buf — Initial address of buffer (choice). your data lives here 🫶
  • count — Number of elements in buffer (integer). how many of them there are 🔢
  • datatype — Data type of each buffer element (handle). what each one IS ✨

📤 OUTPUT PARAMETERS

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

📝 DESCRIPTION

So MPI_File_iwrite_at is the nonblocking version of MPI_File_write_at. it is literally its louder, busier, more independent sibling 💅

It 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. no cap.

The offset is in etype units relative to the current view. That is, holes are not counted when locating an offset 🕳️ The data is written into those parts of the file specified by the current view.

MPI_File_iwrite_at stores the number of datatype elements actually written in status. All other fields of status are undefined ⚠️ (yes, undefined, like, don't go reading them, bestie, they're not yours 🙈).

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 where you find out how it went 🦋

🚨 It is erroneous to call this function if MPI_MODE_SEQUENTIAL mode was specified when the file was open. like. do not. that's a no from the standard ✋

💀 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. 😭 the whole squad goes down.
  • 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. the chill one, it just hands you the error and says "here, you deal with it" 🎀

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. fr fr, it might just Not 💀

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 ATE this one 🌈✨ no cap. this came to you from the Open MPI manual, dated Sep 10, 2026, and yeah — MPI_FILE_IWRITE_AT(3) is the name, don't forget it 💅🦋 mwah, go write some files at offsets, i'm obsessed 🫶💖

📦 where this page comes from