MPI_FILE_IREAD_SHARED(3)

💖 MPI_FILE_IREAD_SHARED 💖

okay bestie, gather round, because this one is literally in the Open MPI manual under section 3 and its whole name is MPI_File_iread_shared ✨

🌸 NAME 🌸

MPI_File_iread_shared — reads a file using the shared file pointer, and it's nonblocking and noncollective. yes queen, both. 👑

---

🎀 SYNTAX 🎀

✨ C Syntax ✨

#include <mpi.h>

int MPI_File_iread_shared(MPI_File fh, void *buf, int count,
     MPI_Datatype datatype, MPI_Request *request)

✨ Fortran Syntax ✨

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

✨ Fortran 2008 Syntax ✨

USE mpi_f08
MPI_File_iread_shared(fh, buf, count, datatype, request, ierror)
     TYPE(MPI_File), INTENT(IN) :: fh
     TYPE(*), DIMENSION(..), 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 — the file handle (a handle, bestie). it goes in and it's just kinda there, living its life.

💜 INPUT PARAMETERS 💜

• count — how many elements are in the buffer (integer).
• datatype — the data type of each buffer element (handle).

🌈 OUTPUT PARAMETERS 🌈

• buf — initial address of the buffer (choice).
• request — the request object (handle).
• ierror — Fortran only: error status (integer).

---

🦋 DESCRIPTION 🦋

MPI_File_iread_shared is the nonblocking version of the MPI_File_read_shared interface — like, same energy, but it doesn't make you wait around for it. 💅 it uses the shared file pointer to read files.

⚠️ ngl here's the tea: the order of serialization among the processors is not deterministic for this noncollective routine. so if you want a specific order among your processors you need to use other methods of synchronization to impose it. it's giving chaos unless you do something about it. 😭

---

💀 ERRORS 💀

almost all MPI routines return an error value, fr fr. for C routines it comes back as the return result of the function, and for Fortran routines it's in the last argument.

before that error value is returned, the current MPI error handler associated with the communication object (e.g., communicator, window, file) is called. if there's no communication object 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 ships three predefined error handlers you can use, and they are iconic in their own ways ✨:

• MPI_ERRORS_ARE_FATAL — causes the program to abort all connected MPI processes. dramatic? yes. effective? also yes. 💀
• 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. respectful. 🫶

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. so like… don't count on it, bestie. 😭

see the MPI man page for a full list of MPI error codes, and see the Error Handling section of the MPI-3.1 standard for more information.

---

👑 Copyright 👑

2003-2026, The Open MPI Community

---

and that's the whole vibe, no cap. this page is from Open MPI, the manual is MPI_FILE_IREAD_SHARED(3), and it was dated Sep 10, 2026. slay, go forth, and don't be nondeterministic about it 💅🌸🦋