MPI_FILE_IWRITE_SHARED(3)

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, in ubuntu stonking

✨ MPI_FILE_IWRITE_SHARED(3) ✨

okay bestie, welcome to the Open MPI manual page for MPI_FILE_IWRITE_SHARED 💖 pull up a chair, grab a boba, we're learning this together.

🌸 NAME 🌸

MPI_File_iwrite_shared — Writes a file using the shared file pointer (nonblocking, noncollective).

like... it writes to a file. but nonblocking. and it's using the shared file pointer. iykyk 💅

🌈 SYNTAX 🌈

bestie there are three (3) ways to say this depending on what language you're in. pick your fighter:

💜 C Syntax

#include <mpi.h>

int MPI_File_iwrite_shared(MPI_File fh, 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_SHARED(FH, BUF, COUNT, DATATYPE, REQUEST, IERROR)
     <type>  BUF(*)
     INTEGER FH, COUNT, DATATYPE, REQUEST, IERROR

💜 Fortran 2008 Syntax

USE mpi_f08
MPI_File_iwrite_shared(fh, buf, count, datatype, request, ierror)
     TYPE(MPI_File), INTENT(IN) :: fh
     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 🎀

so there's exactly one of these and she does double duty, main character energy fr:

  • fh — File handle (handle). it goes in, it comes out, she's doing both 💅

🦋 INPUT PARAMETERS 🦋

the stuff you gotta hand over:

  • count — Number of elements in buffer (integer). just... how many. that's it.
  • datatype — Data type of each buffer element (handle).

🌸 OUTPUT PARAMETERS 🌸

what the function hands back to you:

  • buf — Initial address of buffer (choice).
  • request — Request object (handle). hold onto this one, bestie, you'll need it later 👀
  • ierror — Fortran only: Error status (integer).

💖 DESCRIPTION 💖

okay so, MPI_File_iwrite_shared is a nonblocking routine that uses the shared file pointer to write files. the way that it just... hands you back a request and doesn't wait? iconic. truly not like the other routines.

but here's the thing, bestie, and i need you to hear me on this one:

the order of serialization is not deterministic for this noncollective routine, so you need to use other methods of synchronization to impose a particular order.

translation: she writes in whatever order she pleases 🫶 if you need a specific order, that's a you problem and you gotta bring your own synchronization. no cap.

😭 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. 💀 yeah. everybody. gone.
  • 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. 🙈

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. (yes bestie, the standard. it's giving required reading. do it anyway. 👑)

2003-2026, The Open MPI Community

and that's the whole page, bestie!! 🎀 this one came from the Open MPI manual, dated Sep 10, 2026, and it's filed under MPI_FILE_IWRITE_SHARED(3). go forth and write your files nonblocking-ly, and remember: shared file pointer = no deterministic ordering, so sync up before you ship it. slay 💅✨🦋

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